A COST EFFECTIVE GRASSLAND MANAGEMENT STRATEGY TO REDUCE THE NUMBER OF BIRD STRIKES AT THE BRISBANE AIRPORT

Transcription

1 A COST EFFECTIVE GRASSLAND MANAGEMENT STRATEGY TO REDUCE THE NUMBER OF BIRD STRIKES AT THE BRISBANE AIRPORT Belinda Thomson BAppSc School of Natural Resource Sciences Queensland University of Technology Brisbane, Australia This dissertation is submitted as a requirement of the Masters by Research Degree 27

2 Abstract In an era of acute concern about airline safety, bird strikes are still one of the major hazards to aviation worldwide. The severity of the problem is such that it is mandatory in all developed countries to include bird management as part of airport safety management programs. In Australia, there are approximately 5 bird aircraft strikes per year (Bailey 2). Brisbane airport has a relatively high occurrence of strikes, with an average of 77 recorded every year (22-24). Given the severity of the problem, a variety of techniques have been employed by airports to reduce bird strikes. Scare devices, repellents, continuous patrols for bird hazing, use of raptors to clear airspace of birds and depredation are used by many airports. Even given the diversity of control methods available, it is accepted that habitat management is the most effective long term way to control birds in and around the airport space. Experimental studies have shown that habitat manipulation and active scaring measures (shooting, scaring etc), can reduce bird numbers to an acceptable level. The current study investigated bird populations in six major vegetation habitat types identified within the operational and surrounding areas of Brisbane airport. In order to determine areas where greater bird control and management should be focused, bird abundance, distribution, and activity were recorded and habitats that pose the greatest bird strike risk to aircraft were identified. Secondly, species with high hazard potential were identified and ranked according to their hazard potential to aircraft.

3 II This study also investigated the effectiveness of different vegetation management options to reduce bird species abundance within operational areas of Brisbane airport. Four different management options were compared. Each management option was assessed for grass structural complexity and potential food resources available to hazardous bird species. Analysis of recorded data showed that of the habitats compared within the Brisbane airport boundaries, grasslands surrounding runways, taxiways and aprons possess the greatest richness and abundance of bird species that pose the greatest potential hazard to aircraft. Ibis and the Australian kestrel were identified as the bird species that pose the greatest risk to aircraft at Brisbane airport, and both were found in greatest numbers within the managed grasslands surrounding operational areas at the airport. An improved reporting process that allows correct identification of all individual bird species involved in bird strikes will not only increase the accuracy of risk assessments, but will also allow implementation of more effective control strategies at Brisbane airport. Compared with current grassland management practice, a vegetation management option of maintaining grass height at 3-5cm reduced total bird utilisation by 89% while utilisation of grassland by potentially hazardous birds was also reduced by 85%. Maintaining grass height within the 3-5cm range also resulted in a 45% reduction in the number of manipulations required per year (11 to 6), when compared with current management practices, and a 64% reduction in

4 III annual maintenance cost per hectare. When extrapolated to the entire maintained grass area at Brisbane airport, this resulted in a saving of over $6 annually. Optimisation of potential hazard reduction will rely on future studies that investigate the effect of particular vegetation species that could replace the existing mix of grasses used at Brisbane airport and an understanding of the relative importance of vegetation structure and food supply in determining utilisation by potentially hazardous bird species.

5 IV Table of contents Abstract... I Table of contents... IV List of figures... VII List of tables... I List of appendices... x List of Acronyms... I Statement of original authorship... Ii Acknowledgements... xiii 1. Project Overview The problem Why Birds are Attracted to the Airport Environment Factors Influencing Birdstrikes Bird Size Bird Abundance Bird Behaviour Environmental Factors Techniques to Manage the Birdstrike Hazard Avoidance Techniques Control Techniques Experimental Site Brisbane Airport Current Management Practices Project aims Thesis structure... 17

6 V 2. A RISK ASSESSMENT FOR OPERATIONAL AND SURROUNDING HABITATS AT BRISBANE AIRPORT Introduction Aims Methods Study area Habitat description : Operational areas Habitat description : Surrounding habitats Bird data collection Statistical analysis Results Bird numbers and distribution Bird numbers and distribution by habitat Species richness Monthly and seasonal bird distribution across habitats Daily bird abundance Discussion A BIRD HAZARD INDE FOR OPERATIONAL AND SURROUNDING HABITATS OF BRISBANE AIRPORT Introduction Aims Methods Study area Habitat description Hazard ranking data compilation Results Hazardous bird presence at Brisbane airport Monthly and seasonal hazardous bird abundance and distribution Daily hazardous bird abundance Top ten hazardous bird species and distribution... 46

7 VI 3.5 Discussion Hazardous bird presence at the Brisbane airport Monthly and seasonal abundance of hazardous birds at Brisbane airport Limitations on hazard ranking Habitat hazard ranking and bird reduction recommendations Other recommendations A COST EFFECTIVE GRASSLAND MANAGEMENT STRATEGY TO REDUCE THE NUMBER OF BIRD STRIKES AT BRISBANE AIRPORT Introduction Methods Study area Prior to Manipulation Grassland Manipulation Food Resources Economic analysis Statistical Analysis Results Prior to grassland manipulation Grassland manipulation Food Resources for Birds Economic Analysis Discussion GENERAL DISCUSSION/CONCLUSIONS APPENDICES REFERENCES...1

8 VII List of Figures Figure 2.1 Map showing (a) the location of the study site within Queensland (b) the study site broken into habitat areas and variable circular points in each habitat Figure 2.2 Average number of aircraft movement over a daily period Figure 2.3 Percentage of all bird numbers observed within all habitats at the Brisbane airport Figure 2.4 Number of bird species found in habitats at the Brisbane airport Figure 2.5 Average seasonal species richness for each habitat Figure 2.6 Difference in number of birds per hectare observed in all habitats at the Brisbane Airport Figure 2.7 Yearly bird abundance in each habitat at the Brisbane airport Figure 2.8 Seasonal bird abundance in each habitat at the Brisbane airport Figure 2.9 Difference in birds observed during three periods of the day (a) Number of Birds per hectare (b) Number of birds/ten minutes.. 37 Figure 3.1 Percentage of hazardous birds observed in all habitats on and around the Brisbane airport Figure 3.2 Hazardous birds observed in each habitat at the Brisbane airport Bird numbers/hectare Figure 3.3 Number of hazardous birds observed over a yearly period at the Brisbane airport: Number of birds/hectare Figure 3.4 Average seasonal hazardous bird abundances for each habitat at the Brisbane airport Figure 3.5 Number of hazardous birds observed during the day... 48

9 VIII Figure 3.6 Top ten hazardous bird species (based on weight) and habitats in which they are found at the Brisbane airport Figure 4.1 (a) Grassland management study areas within Brisbane airport Boundaries (b) Site A (c) Site B (d) Site C Figure 4.2 Mean vegetation height (± SE) for all areas before manipulation Figure 4.3 Relative bird utilisation (birds observed/1.92ha/4min) at all sites prior to manipulation (a) All bird species (b) Potentially hazardous bird species Figure 4.4 Mean grass height (± SE) during vegetation manipulation for each treatment over the period June 24-May Figure 4.5 Relative bird utilisation within each treatment (a) Total (b) Monthly...7 Figure 4.6 Relative bird utilisation of potentially hazardous birds within each treatment (a) Total (b) Monthly...72 Figure 4.7 Relative bird utilisation (bird observed/1.92ha/4mins) during the day (a) all bird species (b) potentially hazardous bird species...74 Figure 4.8 Aircraft movements at Brisbane airport...75 Figure 4.9 Ground dwelling invertebrate abundance for each treatment type. (Mean ± SE) Figure 4.1 Foliar invertebrate abundance for each treatment type. (Mean ± SE) Figure 4.11 Dry weight of grass seeds collected from treatments (Mean ± SE) Figure A.1 Grassland management regime for Brisbane airport... 98

10 I List of Tables Table 2.1 Maximum number of each bird species recorded at Brisbane Airport; % of total number of birds for each species; % of total bird numbers for each species in each habitat Table 2.2 Numbers of bird species observed in each habitat over a yearly period Table 3.1 Bird strike data, weights and hazard ranking for bird species found at the Brisbane Airport Table 4.1 Non hazardous and potentially hazardous birds observed in each site before manipulation Table 4.2 Mean grass height (± SE) for each treatment over the course of the study Table 4.3 Relative bird utilisation (birds/1.92ha/4mins) of treatment type (mean ± SE) for hazardous, non hazardous and all bird species over the period of the study Table 4.4 Utilisation of treatments by bird species Table 4.5 Complete count of invertebrates and vertebrates (Order/Class) sampled from pitfall traps Table 4.6 Dry weights of grass seed species sampled from all treatments. 79 Table 4.7 Mean direct costs associated with the maintenance of the various grass height treatments...8

11 List of Appendices Appendix 1 Species identified as present within habitats Appendix 2 Bird stikes Appendix 3 Grassland Management Strategy... 96

12 I List of Acronyms ATSB - Australian Transport Safety Bureau BAC - Brisbane Airport Corporation BAM - United States Bird Avoidance Model GIS - Geographic Information System USGAO - United States Government Accountability Office

13 II statement of original authorship The work contained in this thesis has not been previously submitted for a degree or diploma at any other educational institution. To the best of my knowledge, this thesis contains no material previously published or written by another person except where due reference is made. Belinda Thomson April 27

14 III Acknowledgements This study was funded by Brisbane Airport Corporation Limited (BAC) and Queensland University of Technology (QUT) as part of an Australian first partnership for an airport and university. There are many people to thank: Dr John Wilson, Peter Mather, David Elmouttie, Brendan Farthing and Peter Prentis for their guidance, statistical prowess and manuscript editing, John McCaffery, Karyn Rains, Phil Randall and Brett Forknall of BAC for their organisational abilities. The security personnel from Gate 1 at BAC for their patience and the maintenance crew of BAC especially Clint Roberts and Geoff Barton, without whom the study could have been accomplished. I would also like to dedicate this paper to the memory of my supervisor Dr John Wilson, who was and ever shall be a treasured and epochal part of the world in which I live.

15 Chapter 1. Project Overview 1 1. Project Overview 1.1 The problem Since the inception of flight in the 19 s, men have been competing not just with each other for air space but also with avifauna. The Wright brothers were the first to experience problems with birds and aircraft early in the history of flight, (Rao & Pinos 1998). The first human fatality associated with flight in 1912 was attributed to a bird, when a gull became entangled in the flight controls of an early model aircraft resulting in a crash (Solman 1978; Rao & Pinos 1998; Thorpe 23). Although bird and aircraft interactions were only a minor concern for early aviators, this issue has become a major consideration for modern aviation. Around the world, instances of birdstrikes in civilian and military aviation are estimated to approximate 3, every year (ATSB 22). Strikes incur many costs. The most devastating of these is loss of human life. Since 1912 there have been 231 aviation fatalities linked to birdstrikes (Thorpe 23). The secondary cost of bird strikes includes; loss of aircraft, costly repairs and loss of flight time due to avifaunal strikes or avifaunal interruptions to flight schedules. The most expensive of these is loss of aircraft due to birds. Since 199, 115 aircraft have been lost worldwide (USGAO 21) bringing the total of both military and civilian aircraft lost due to birdstrikes to more than 2 since the beginning of human aviation (Allen 2). After loss of aircraft, repair bills for damage caused by bird collisions and the loss of flight time due to inoperative aircraft are the next major contributors to monetary cost of bird strikes. Each year worldwide, between 1.2 and 4 billion US dollars are spent in the aviation industry to rectify damage caused by avifauna (Short et al. 2; Allen & Orosz 21). These figures are such that around the world today most airports attempt to control wildlife hazards in and around the aerodrome environment as part of stringent management regimes.

16 2 Chapter 1. Project Overview Due to a lack of reliable reporting, total actual strikes may be much greater than previously estimated. Reporting of birdstrikes around the world has yet to be standardised. Every aerodrome has its own regulations, and reporting of many birdstrikes may not even occur when there is no evidence of damage to aircraft or pilots are unaware that aircraft have been impacted (Van Tets 1969A; Burger 1985; Brown & Hickling 2). In order to develop effective management plans, reporting of all birdstrikes is essential (ATSB 22). Previously, insufficient reliable information was collected on birdstrikes (Blokpoel 1976) and information that was documented may have been biased as pilots are more likely to report incidences with larger bird species than those involving small individuals (Chilvers et al. 1997; Linnell et al. 1999). Although birdstrikes numbers are reported each year the actual number of birdstrikes may be up to 8% more than estimated previously. In Australia, an estimated 5 strikes occur per year (Bailey 2). In the past, reporting of birdstrikes in Australia happened only when damage resulted to an aircraft (ATSB 22), which may mean the real number of strikes in the past 1 years may be up to 5% higher than statistics suggest (ATSB 22). In other countries (e.g. Canada and the USA), estimates suggest that only 15 to 3 percent of all birdstrikes are reported (ATSB 22). In the USA alone, actual number of birdstrikes may be up to more than 8 times that recorded in original reports (Eschenfelder 23). In spite of biases associated with reporting of birdstrikes, there is reliable evidence to suggest that they have increased in number due to several factors. Modern aircraft numbers are increasing and they are constructed with quieter engines that are also capable of greater speed than in the past. This increases the probability of birdstrikes (Solman 1981). Birds have less time to react and avoid aircraft that approach them at faster speeds with less noise. This may also explain why birds are involved in an increasing number of strikes within airport environments. Aircraft takeoff requires a great burst of speed to enable lift off and reaction times for birds are short. In addition when

17 Chapter 1. Project Overview 3 planes land, aircraft noise is reduced and this further reduces reaction time by birds at airports (Jacobi 1996). Most bird species fly at relatively low altitudes (except for migratory birds) and most incidences of bird and aircraft collisions occur below 1m (Barras & Wright 22). Therefore possibility of strike is greater during takeoffs and landings (Stables & New 1967; Barry 1974; Linnell et al. 1996; Rao & Pinos 1998; Short et al. 2; ATSB 22). Military aircraft flying at low altitudes (training and reconnaissance flights) and at great speeds are particularly vulnerable (Gunn & Solman 1967; Stables & New 1967; Sodhi 22). In Australia from , 52 percent of all reported birdstrikes within the civilian sector occurred during aircraft approach and landing, while 33 percent occurred during take off and initial aircraft assent (ATSB 22). In contrast, in the military sector at least 28 percent of reported birdstrikes occurred during flight at low altitudes (ATSB 22). These figures are indicative of statistics worldwide. In the absence of specific bird management plans, incidence of birdstrikes are expected to increase due to increasing frequency of aircraft flights (ATSB 22). Scientifically based management strategies to control birdstrikes are therefore required urgently. The first step in developing such strategies will be to; investigate major hazards on and around the aerodrome environment, determine the risks they pose, and identify the most effective ways to reduce risk (Allen 2). 1.2 Why Birds are Attracted to the Airport Environment Most airport environs range from manicured areas for aesthetic appeal, large areas of grassland and even agricultural crops between runways, to surrounding urban and uninhabited areas including bushland, wetlands and waste disposal areas. The main appeal of most airports for birds is the availability of large areas of short grassland that is maintained continuously between and around runways, taxiways and aprons. Birds come to these

18 4 Chapter 1. Project Overview areas to feed, drink, and rest and sometimes to nest or roost (Eschenfelder 21; ATSB 22). Smaller birds are believed to feel more secure when feeding in short-grassed areas as they provide a wide field of vision for detecting predators (Devereux et al. 24). The fact that grass areas are maintained continually means that insects and other invertebrates on which birds feed are constantly disturbed which may lead to easier detection of prey. It may also be more energy efficient for certain birds to forage for seeds and invertebrate prey in short grass rather than having to expend more energy searching through long grass (Butler & Gillings 24). Birds that feed in short grass may in turn attract larger bird predators (Eschenfelder 21 ; ATSB 22), which may constitute greater problems to aircraft than will smaller birds. Large birds with large body mass pose a greater hazard to aircraft in the event of a collision than will small birds (Dolbeer et al. 2). Other resources for birds are also provided by airport environments. Water is available from drainage areas, spillways, and even standing water in lower areas of airfields after rain. Rain may also force insects and other prey out of the soil and onto hard surfaces such as runways, which provide easy foraging environments for many bird species. Roosting perches or vantage points for birds of prey are often available in the form of aircraft hangars, runway signs, lights and vegetation such as dead trees around the perimeter of the airfield. The airfield can also offer safety from larger predators including humans (Wright 1967). Around airports, natural or modified environments such as wetlands, refuse tips, bushland and agricultural areas may also contain resources that attract bird species (ATSB 22). Roosting and breeding sites and food may act as attractants for birds to these areas. Even though birds may spend most of their time in the areas surrounding the airport, there are usually times during the day they will cross the airspace of the aerodrome to reach resources and thus potentially interact with aircraft. Therefore surrounding environments at

19 Chapter 1. Project Overview 5 airports need to be considered along with the actual airport grounds when considering potential avifaunal hazards and their prevention or control. 1.3 Factors Influencing Birdstrikes Birds on airports constitute a real danger to aircraft, although not all species may be equally hazardous. Factors including, individual size, relative abundance and intra-specific behaviour need to be taken into account before determining if individual species pose a threat to aircraft (Allen 2) Bird Size As noted earlier the larger and heavier an individual is, the greater a hazard it will present to aircraft because size and weight influence potential for damage (Milsom 199). Having said this, even small birds can cause serious damage. The risk of damage to aircraft from small birds becomes greater when they are in large numbers due to a greater chance of multiple strikes (Sodhi 22) Bird Abundance Flocking species will have a greater chance of causing significant damage to aircraft in the event of a collision due to potential for multiple strikes and/or ingestion into engines (Sodhi 22). Even though there is a greater risk of damage with flocking species, the behaviour of large groups of birds often enables early detection by approaching aircraft at a greater distance than will a singular individual (Jacobi 1996). Seasonal migratory species have high potential for striking aircraft more often than non-migrating species, as migratory birds, especially large bodied species, commonly fly in large groups to conserve energy (Hummel 1983; Weimerskirch et al. 21). Migratory species are also unfamiliar with

20 6 Chapter 1. Project Overview the hazards posed by aircraft and may be relatively inefficient at detecting approaching aircraft (Sodhi 22). Migrating species are also more likely to be involved with strikes due to fatigue (Sodhi 22) as some migrate tens of thousands of kilometres. Bird species that are residents at airfields can develop avoidance behaviour and hence may not pose as significant a threat of collision as seasonal migrating species. Thus relative abundance, size and familiarity with the airfield environment can contribute to bird strike probability Bird Behaviour Behaviour of certain bird species may increase their birdstrike potential. Juveniles may pose significantly higher risks than adults as a result of a lack of learned behaviour from parents to avoid aircraft (Jacobi 1996), or they may be less able to avoid aircraft once a danger is perceived because of inexperience in manoeuvrability and/or lack of strength (Solman 1981; Sodhi 22). Some birds are opportunistic feeders and can take advantage of potential food resources that are disturbed when maintenance is carried out on grasslands surrounding runways. As a result, birds feeding on these resources can be brought into closer proximity with aircraft, which may increase the risk of a birdstrike Environmental Factors Although some birds are active during all hours of the day and during the night most activity usually occurs in the first hours after sunrise (Robbins 1981). Higher activity rates at this time, means that strikes are more likely to occur during these times, although this is not always the case, as birdstrikes have been reported over the complete 24 hour period (Blokpoel 1976). Most however, occur during the day, a small proportion happen at night,

21 Chapter 1. Project Overview 7 but only a relatively small proportion of strikes happen in the early morning periods (Neubauer 199). The length of daylight hours may also affect risk of birdstrike. Most bird/aircraft collisions occur in late summer and early autumn (Kelly et al. 23) when hours of daylight are longer, compared with numbers of strikes in late autumn and early winter. Along with daylight length, intensity of light can also have an impact on bird behaviour and an individual s ability to avoid collisions with aircraft. Research is underway to determine the effect that ambient light conditions may play on birdstrike potential (Fennessy et al. 23). Weather conditions can also affect bird behaviour. Inclement weather may alter some bird species foraging behaviour and this lull in activity also reduces potential for birdstrike during these times (Neubauer 199; Manktelow 2). 1.4 Techniques to Manage the Birdstrike Hazard Birdstrike reduction is a major issue for airports and aerodromes around the world and as each airfield has its own set of circumstances, management of bird presence varies. In order to manage bird populations or reduce birdstrikes effectively there are many options that can be applied at most airports, each with differing rates of success. They can be separated into two broad categories: Avoidance Techniques Control Techniques a. Dispersal b. Habitat Management

22 8 Chapter 1. Project Overview Avoidance Techniques Due to the fact that the airport environment is attractive to many bird species (Wright 1967), it is often very difficult to stop all birds from entering. To address this, systems have been developed to act as a warning to both airport and aircraft personnel of potential bird hazards. There are different ways to determine bird presence around the airport vicinity, including detection technology such as radar that can pick up presence of birds in large numbers, or routine reports by airport security patrols. Use of radar for bird hazard advisory systems began in the 196 s when radar systems regularly detected echoes that at first could not be identified (Schaefer 1967). A vast majority of these echoes, termed point angels, were later found to be birds (Schaefer 1967). Since the first detection of birds by radar, radar ornithology has progressed significantly. Radar is now used to track migrating birds and to warn airports within bird flight paths, so that avoidance strategies and birdstrike warnings can be activated (Leshem & Froneman 23; Ruhe 23). Unfortunately birdstrike warnings from radar usually happen only after avian groups are detected. The United States Air Force Bird Avoidance Model (BAM) is used to predict when groups of migrating birds will arrive. It was developed in the early 198 s and uses historical population data on waterfowl and raptors to predict birdstrike risk for low level aircraft training routes (Lovell & Dolbeer 1999). Early versions of BAM were limited in their use, but with the introduction of Geographic Information Systems (GIS), BAM now is able to display a birdstrike risk for areas of 1km over the entire US land mass (DeFusco 2). This ability to predict where and when bird hazards are likely to occur in the United States has saved millions of dollars for military aviation. There is a great need to apply this technology more widely.

23 Chapter 1. Project Overview 9 A pilot s knowledge of conditions around airports and likely presence of birds can do much to minimise and avoid birdstrikes (Eschenfelder 21). Warnings from the airfield tower about presence of birds in the area help to reduce risk of birdstrikes as can information from personnel around the runways and taxiways. Employing warnings that result in pilots avoiding hazards can reduce the number of birdstrikes, yet it does not decrease the hazard itself. Fewer birds present on airfields will result in fewer birdstrikes. Different techniques can be employed to control the number of birds present in airport habitats and these will be discussed next Control Techniques There are many tactics employed by airports around the world to try to reduce the number of birds that occur within aerodrome domains. These can be divided into two distinct approaches: dispersing and dissuading birds from remaining after they have arrived or initially deterring their arrival by manipulating the local environment so that birds do not find aerodrome habitats favourable Dispersal Techniques Removal of bird species from areas where aircraft operate has been a management strategy that has been trialed at almost every airfield that has experienced bird hazards. Many techniques have been applied with varying degrees of success. The most widely used today include: shooting; frightening devices, involving pyrotechnics and electronic devices like bird distress calls; and use of predatory stimuli.

24 1 Chapter 1. Project Overview Shooting or culling birds, can reduce the physical number of birds present and hence can reduce birdstrike probability (Dolbeer et al. 1993). This practice is often not favoured and depredation is a last resort. It is only carried out after special permits are obtained from local authorities. Some bird species have even been shown to alter their flight path to avoid aerodromes that employ shooting as part of their bird management strategy (Dolbeer et al. 23). The problem can be however, that territory that was formerly occupied is now open for other bird species to invade (Van Tets 1969 A). This can raise an additional problem, as birds filling vacant niches may be less experienced with aircraft avoidance and therefore risk of strike may increase (Burger 1983). Pyrotechnics and the use of bio-acoustics or amplified bird distress calls have also been shown to be successful for removing birds from airfields (Busnel & Giban 1967; Baxter 2; Ryjov 2). Pyrotechnics employ the use of visual and audio aids to scare birds away from areas if a threat is perceived. Devices such as shell crackers which are fired from a shotgun and explode loudly, force many bird species into flight but if they are used in isolation, birds eventually habituate to the noise reducing their effectiveness (Blokpoel 1976; Baxter 2). Another technique employed to deter birds from airports is the use of taped distress calls that target specific bird species. Tapes of warning calls or distress calls of specific species of bird are replayed over loud speakers in areas where the species aggregate. This techniqe has been shown to work with certain species of bird on airfields (Busnel & Giban 1967), but with some flocking birds initial flight is followed by an investigation of the source of the calls which usually results in only slow departure from the airfield space (Busnel & Giban 1967). Depending on bird species, use of distress calls may actually attract birds to the calls first instead of scaring them away (Airforce 1997). This can increase strike risk and application of this technique needs to be timed so as to ensure that dispersal occurs before the next aircraft arrival

25 Chapter 1. Project Overview 11 or departure (Brough 1967). Limitations of dispersal techniques include that; they can take an extended period of time to work, and the use of bioacoustics is also an expensive alternative that requires high maintenance. The approach has been efficient at some airports while completely ineffective at others (Ryjov 2) even when used in conjunction with other control methods. This is because birds tend to habituate to the calls (Baxter 2). Another control method that has proven to be successful when used in conjunction with distress calls, are use of predatory species. Using an animal or bird species that hazardous species would usually be wary of such as birds of prey or dogs have proven effective. Distress calls are sometimes used that usually attracts target species and then predatory species are released resulting in hazardous species leaving the aerodromes in large numbers (Tomsons 1998). Falconry programmes are in place at some airports around the world and can greatly reduce the number of birdstrikes (Tomsons 1998). Although falcons can be an extremely effective control method, they have many disadvantages. Both birds and handlers need extensive training, birds cannot be used during inclement weather and they cannot be flown at night (Brough 1967). Some airports have employed dogs to disperse birds from airport habitats, with great success, resulting in a reduction of 29 to 4 percent in hazardous species and up to a 5 percent reduction in bird numbers (Patterson 2; Carter 23; Froneman & Van Rooyen 23). Reduction of bird numbers, in turn, will reduce the number of birdstrikes, and the use of dogs has at some airports reduced the instances of bird strike to zero (Patterson 2; Carter 23; Froneman & Van Rooyen 23). Although employing predators has been successful there are high associated costs that may render this technique a major problem at many airports.

26 12 Chapter 1. Project Overview All of the techniques used currently to actively scare or remove birds from airfields may be useful when used in conjunction with other applications. Most work for only a short period of time however, before habituation and other factors make them inefficient. An alternative strategy used at a number of airports around the world to reduce numbers of birds is that of long term manipulation of the airport environment to make it less appealing to hazardous bird species (Mead & Carter 1973; Brough & Bridgman 198; Buckley & McCarthy 1994; Crossfield 21). This approach will differ for individual airfields taking into consideration differences in surrounding habitat, what hazardous avifaunal species are present and financial constraints Habitat Management Techniques In order to remove or reduce hazardous birds from airports, factors that attract birds need to be reduced or removed. A large proportion of airports around the world maintain grassland between and around the operational areas (runways, taxiways and aprons). Maintenance of grassy areas to a specific height has been shown to reduce numbers of certain bird species that may be a hazard to aircraft (Mead & Carter 1973; Brough & Bridgman 198; Buckley & McCarthy 1994; Crossfield 21). Many bird species are attracted to short grass (5-1cm) for feeding, resting and safety reasons. Areas of short grass can offer birds a large area of easily accessible food in the form of invertebrates that thrive in the fertile soils of continuously mown areas. Associated with ease of food access is the safety associated with short grass as birds can gain good line of sight for detecting predators (CAA 22; Devereux et al. 24). The long grass policy (Mead & Carter 1973), that has been adopted at some airports, maintains the length of grass at 15-2cm or higher to dissuade use by birds (Brough & Bridgman 198; Buckley & McCarthy 1994). This policy is based on the premise that long grass deters birds from foraging for

27 Chapter 1. Project Overview 13 invertebrates and that it also reduces bird acuity thus making these areas less secure to rest and feed (Dekker 1996). However, the approach does have some disadvantages. Maintaining long grass on airfields may actually increase soil fertility in turn increasing invertebrate numbers. Numbers of prey for birds can thus actually increase (Dekker 1996). This results from the requirements for maintaining long grass. Each spring the long grass is cut down and removed. The area is then fertilised to ensure rapid and lush growth of new grass. Maintenance for the rest of the year involves cropping the grass when it gets to a specified length (Deacon & Rochard 2) but usually the cropped grass is left and decomposes providing additional fertilisation for the grassed areas until it is removed again during the spring cutting. Long grass may also become a preferred habitat for nesting birds and birds that forage in longer grasses (Seamans & Dolbeer 1999) which may add to aircraft hazards. Rodents and other small vertebrates may also find long grass satisfies their specific needs, in turn attracting larger birds of prey which prove to be a greater hazard to aircraft due to their flight behaviour when searching for prey. Another approach to make airfield grounds less appealing to unwanted avifauna species requires maintaining a poor long grass regime. This application, while still maintaining a specific length of grass, focuses on reducing soil fertility (Dekker 1996, 2). This is accomplished by not fertilising the grass each cycle and removing clippings after the grass has been cut to the required length. Regular removal of grass clippings is however a costly method in view of the time and man power required and the need to remove clippings to areas that will not be disturbed by aircraft (BAC pers comm). This can require transport to areas outside the airport environment which requires extra time, effort and cost. Reduction of biomass may also render areas surrounding the runways subject to erosion from engine thrust. This can jeopardise aircraft safety.

28 14 Chapter 1. Project Overview An alternative habitat manipulation approach involves replacing grass with alternative plants that are less appealing to hazardous bird species (Blockpoel 1976, 23). The choice of the replacement vegetation must suit requirements of being unattractive to both birds and invertebrates as both a food source and an area of cover (Austin-Smith & Lewis 197). This needs to be adapted independantly for each airfield taking into consideration the species of birds determined to be most hazardous. Replacement of vegetation can be extremely costly however, but the long term benefits may outweigh initial outlays (Wright 1967). Other procedures for bird control that have been trialed include: changing colour of landing lights to reduce insect attraction and therefore indirectly reducing the number of birds that prey on this source of food (Van Tets et al B); spraying chemicals to poison or disperse birds (Blokpoel 1976; Engeman et al. 22); use of insecticides to reduce the abundance of food resources for birds (Engeman et al. 22); adapting infrastructure on the airfield to reduce bird structural attractants (Tomlin et al. 1981; Dekker 23); manipulating habitats surrounding airports that may be roosting areas for birds considered hazardous to aircraft (Weitz 23); or manipulating attractive areas outside the airfield such as land fill sites that may cause birds to fly over the airfield in order to reach the resource (Cleary & Dolbeer 1999). Although there are a variety of bird hazard management approaches, none are considered as standard at all airportss or aerodromes. While habitat management is generally considered to offer the best reduction in numbers of birds over a period of time, birds can still be found in unattractive habitats from time to time (Wright 1967). Dispersal and habitat management approaches used in combination are likely to provide the best solution for decreasing the bird numbers at airports. Specific approaches must however, be adapted to each new situation.

29 Chapter 1. Project Overview Experimental Site Brisbane Airport The Brisbane airport is located 13 km north east of the centre of Brisbane and covers 27 hectares of land. Original vegetation has been cleared extensively and now only seven main vegetation communities are found within the airport boundaries. In the past, Brisbane airport has not had a great problem with avifauna associated with these habitats, and the birdstrike rate was relatively low. From 1966 till 1973, there were a total of 14 birdstrikes recorded and most resulted in no damage (Barry 1974). Today however, Brisbane airport has one of the highest strike rates of any Australian airport each year. The number of strikes averaged 33.2 per year from (Pell & Jones 22), and since then there were 71 reported in 22 (Rhodes & Jones 24), 79 reported in 23 (pers comm. BAC 24) and 81 reported in 24 (pers comm. BAC 25). Thus the need to develop more effective bird hazard management plans for the Brisbane airport has been recognised as a priority for airport management Current Management Practices Brisbane airport has already instigated some management plans to deal with potential bird hazards. A large tree plantation, regarded as poor fauna habitat (BAC 1999), was established with a monoculture of Casuarina glauca in order to render surrounding habitats at the airport, unattractive to birds. In addition, a local refuse tip that was originally near the airport was found to be attracting large numbers of Silver Gulls (Larus novaehollandiae), which were also using the airfield grounds as a resting area. The refuse tip was relocated and the number of gulls recorded at the airport subsequently, was reduced to zero. Removal of shallow-water feeding areas and bird attracting wetlands has also been incorporated in the management plan for avifaunal species found at the Brisbane airport (BAC 1999). The Brisbane airport also employs a bird dispersal technique, cracker shot (exploding cartridges fired from a shot gun),

30 16 Chapter 1. Project Overview that helps to dissuade birds from using the airport grounds. Although these management plans are in place, instances of birdstrikes still remain high. 1.6 Project aims In order to reduce bird strike risk, more action needs to be taken. Identification of areas that can be considered as a hazard to aircraft and an extensive risk assessment are required. The Brisbane airport lacks a defined scientific habitat management option for the vast grasslands surrounding runways, taxiway and aprons to encourage birds to go elsewhere. Any habitat management scheme should be aimed at deterring use by the most hazardous bird species present at the Brisbane airport. Accordingly this study aims to: (1) Determine habitats within the Brisbane airport boundary that are most hazardous to aircraft in relation to bird abundance and activity so that management can be directed specifically at these areas (Chapter 2); (2) Assess historical bird strike data at Brisbane Airport to determine which bird species are hazardous to aircraft and combine this knowledge with findings from Chapter 1 to identify areas that are considered to offer the greatest potential for bird strikes. Once these areas have been determined, effort can be directed at reducing bird strike potential according to a weighted scale from greatest to least hazard potential (Chapter 3); (3) Determine a vegetation management strategy for the habitat(s) determined to be most hazardous with regard to bird utilisation. Vegetation management will need to be cost effective and efficient at reducing number of potentially hazardous bird species within the airport environment (Chapter 4).

31 Chapter 1. Project Overview 17 Results from the experiments conducted here will provide the Environmental Management Team at the Brisbane airport with options for better habitat management techniques that will decrease the number and species of birds found at the Brisbane airport and therefore in turn reduce the risk and instance of birdstrike. 1.7 Thesis structure Each chapter within this thesis covers specific issues that builds on the results of the previous chapter. Thus, the thesis presents a logical sequence of the ideas necessary to develop a scientific management strategy to reduce number of bird strikes at the Brisbane airport. Each chapter provides sufficient background information so that they may be read and understood seperately (and due to this the methods section of chapter 2 and 3 - Study area and habitat description are repeated). The thesis concludes with a general discussion of the results of each study and their implications for management now and research directions identified for the future.

32 18 Chapter 2. A risk assessment of Brisbane Airport habitats 2. A RISK ASSESSMENT FOR OPERATIONAL AND SURROUNDING HABITATS at BRISBANE AIRPORT 2.1 Introduction Bird strikes are a major hazard to aircraft. Annually, civilian and military aircraft are involved in over 3 birdstrikes around the globe (ATSB 22). Bird strikes have resulted in a significant loss of human life with 231 human related fatalities since 1912 (USGAO 21). The accumulated cost of bird strikes has been estimated at between 1.2 and 4 billion US dollars in repairs and other associated costs (Short et al. 2; Allen 22). As a consequence, most aerodromes around the world incorporate a management regime that focuses on reducing bird presence within and around the airport environment. Birds are attracted to airport environments for many reasons. Most aerodromes have large grassland and vegetated areas and these habitats offer significant opportunities for foraging, nesting and many other habitat related requirements (eg. water for drinking and areas for roosting) (ATSB 22). The main appeal of many airports for birds are large areas of short grass that are maintained continually between and around runways, taxiways and apron areas. Birds come to these areas to feed, drink, and rest and sometimes to nest or roost (Eschenfelder 21; ATSB 22). Some smaller species may select short-grassed areas when feeding as these areas may provide them with a wider field of view to detect predators (Mead & Carter 1973). The fact that grassy areas are maintained continually means that insects and other invertebrates that birds feed on are constantly disturbed and easily visible, which may allow birds to expend less energy when foraging for prey.

33 Chapter 2. A risk assessment of Brisbane Airport habitats 19 Most management options employed at airports for controlling birds are costly and time consuming and are often designed to scare birds away from the airport environs. Scare options are usually rendered inefficient after prolonged use as many bird species can habituate to the noxious stimuli employed (eg. visual and auditory scaring techniques) (Blokpoel 1976; Baxter 2; Ryjov 2). Another effective method for managing bird presence has been to manipulate favoured habitats within the airport and surrounding areas (Solman 1969, Burger 1983, Buckley & McCarthy 1994). With proper management, airfields and their surrounds can be converted into areas that birds find less attractive and hence numbers can be reduced. Combining habitat manipulation with strategic bird scaring techniques is generally considered to be the best approach for controlling bird populations at airports (Solman 1969; Burger 1983; Rao & Pinos 1998; Bailey 2). Australian airports are familiar with the hazards of bird strikes. The Brisbane Airport is one of Australia s major airfields and regularly reports a high number of aircraft/wildlife strikes (ATSB pers comm.) with 79 strikes reported in 23 (67 of them involved birds). Although Brisbane airport employs scare tactics (use of cracker shot - exploding cartridges fired from a shot gun) as the main bird deterrent, the number of bird strikes has increased over previous years. This clearly demonstrates a need to develop improved management options. Management options must reduce the number of birds present on and around the airfield and also be cost effective. Brisbane Airport is an area that contains many different habitats both within the operational zones and the surrounding areas that have potential for attracting bird species that are hazards for aircraft. As a starting point for developing better management regimes for birds at Brisbane Airport, a study of bird diversity and density in airport operational areas and surrounding habitats is required to determine the habitats that contain the greatest abundance of bird life and therefore that could attract birds that may pose

34 2 Chapter 2. A risk assessment of Brisbane Airport habitats a risk to aircraft. Major habitat types and their distribution and abundance at Brisbane airport need to be defined and a risk assessment for each area needs to be carried out, in relation to the bird species that are present there. 2.2 Aims The objectives of the bird risk assessment were to: (1) Assess avifaunal population parameters including species present, relative abundance, habitat areas utilised and peak activity periods (seasonally, monthly and daily). (2) Identify habitat types at Brisbane airport that contain the greatest abundance of bird species. 2.3 Methods Study area Brisbane Airport is Australia s third busiest international airport and operates two major runways. The airport is located 13km Northeast of Brisbane (153 o 6 59 E; 27 o 23 9 S) and occupies an area of 27 hectares. The Airport lies on a reclaimed floodplain close to the mouth of the Brisbane River and is bounded by Moreton Bay Marine Park to the North, Jackson Creek marine habitat and mangroves to the North West, Boondall Wetlands to the West and Boggy Creek and Bulwer Island to the East. The 27 hectares covered by the airport contains seven different major habitat types both within the operational and surrounding areas of the airport (ERM 22). Of the seven different habitat types, two are present in operational areas (directly influenced by the movement of aircraft) and all others occur in surrounding areas.

35 Chapter 2. A risk assessment of Brisbane Airport habitats Habitat description : Operational areas Managed grasslands Managed grasslands surround the runways, taxiways and aprons of both the international and domestic terminals. These areas contain a diverse array of species of grass, sedges and broad leaf plants and are subject to invasion of many weed species, especially in areas that are not maintained frequently by mowing. Common species found within the managed grassland areas include Couch (Cynodon dactylon), Rhodes Grass (Chloris gayana), Kikuyu Grass (Pennisetum clandestinum), Spring Grass (Eriochloa procera), and Paspalum (Paspalum dilatum) (ERM 22). The large grassland areas provide ideal habitat for many bird species in the form of grass seed, insects and standing water after rainfall Unmanaged grasslands Unmanaged grasslands are located adjacent to, and at either end, of the main runway. Species composition include dense wetland communities of mostly reeds (eg Common reed - Phragmites australis) and sedges (eg Bunchy Sedge - Cyperus polystacyous), but also some varieties of grass and weed species that have been left to grow to full size including Rhodes Grass and Groundsel Bush (Baccharis halimifolia) (ERM 22). These areas provide shelter for some reptiles, and mammals which may in turn attract species of birds such as raptors that prey on them. Unmanaged grassland also provide requirements for some grass dwelling and wading bird species.

36 22 Chapter 2. A risk assessment of Brisbane Airport habitats Habitat description : Surrounding habitats Casuarina plantations Very large plantations of Swamp oak (Casuarina glauca) were established around operational areas at Brisbane Airport, as casuarinas are known to be a habitat not favoured by most avifauna (BAC 1999). In the years since planting, undergrowth species such as Lantana (Lantana camera), Wild Tobacco (Solanum mauritianum) and other weed species have become established in the plantations, providing additional habitat for some bird and mammal species (ERM 22). Within the Casuarina plantation are small remnants of emergent vegetation such as eucalypts (Eucalyptus spp) which may also provide nesting opportunities for some bird species Canal, freshwater wetland and sedge communities These areas are similar in plant species composition to the operational unmanaged grasslands but also contain emergent vegetation including casuarina (Casuarina spp), and eucalypt species that supply some larger bird species with roosting, nesting and observation points Mangrove forests Mangrove communities at Brisbane airport include both remnant areas surrounding the larger creeks (Jackson Creek, Serpentine Creek and Serpentine Creek Inlet) around the airport, and new colonies that have established in the canals constructed within the airport s operational boundaries (Airside) and in canals outside the operational boundaries (eg Schulz Canal, Landers Pocket Drains). Species include Grey Mangrove (Avicennia marina), River Mangrove (Aegiceras corniculatum), Yellow Mangrove (Ceripos tagal var australis) and the Red Mangrove (Rhizophora

37 Chapter 2. A risk assessment of Brisbane Airport habitats 23 stylosa) (ERM 22). Tidal mudflats and salt marsh communities are also present within some mangrove areas. These areas provide aquatic bird species and migratory waders with an ideal substrate for foraging and also roosting areas that are not easily accessible to many predators Coastal dunes and foreshore Foreshore habitat at Brisbane Airport is made up of mudflats and sandy flats at low tide. The dunes system is small and confined to the northern end of the airport and the Serpentine Inlet. It contains some species of casuarina, a long strip of maintained grassland and patches of unmanaged grassland. The Serpentine inlet is tidal but retains a large amount of water in a lake setting at low tide. The large area of mudflats provides excellent grounds for migratory waders to feed, as well as many areas for roosting. The Serpentine Inlet also provides areas for aquatic bird species such as ducks and herons to rest and forage Landscaped areas These areas are maintained grassland with planted native and exotic species that run the length of airport drive. As no manipulation is contemplated to reduce the presence of bird species in these areas, they were not considered further here Bird data collection Maps of the Brisbane airport showing each habitat type were divided into 25m 25m grids to allow reference points to be located at least 25m apart in closed habitats and 5m apart in open habitats (Ralph et al. 1993). Within each habitat three points were chosen at random giving a total of 18 points (Figure 2.1). Only a single observer was used to reduce observer

38 24 Chapter 2. A risk assessment of Brisbane Airport habitats bias, so more points were not established. These points became the centre for a variable circular point count (Reynolds et al. 198 DeSante 1986), conducted monthly for twelve months. Each point on the non operational area was marked with a stake and then circles radiating 1m were marked in the cardinal directions with flagging tape, for 4m. Within the operational area, no markers were placed as these were potential FOD (Foreign Object Damage) for aircraft. Instead estimations of -1m, 1-2m, 2-3m, 3-4m and <4m, were used. The bird census took place every month (July 23 June 24), over a period of three days. Each day was divided into three census periods; three hours after sunrise, three hours over the midday period, and three hours before sunset. Times were chosen to represent periods of greatest activity for bird species (Robbins 1981) and also during the major operational times for aircraft at the Brisbane airport (peak aircraft movement morning, midday and late afternoon/early evening) (Figure 2.2). Two habitats were visited each day, with each of the three points within each habitat visited in each of the three time periods. Order of visitation was randomised prior to commencement of observations. Half an hour was allowed at each point, to enable travel between census points within the three hour allotted time period. A period of ten minutes was spent at each point (Reynolds et al. 198; Fuller & Langslow 1984), after a settling period of one minute (Reynolds et al. 198; DeSante 1986; Rosenstock et al. 22), and all birds within the designated areas were identified to species using both sightings and bird call. The data were recorded for each radiating circle, and separated into three time periods, -3mins, 3-6 mins and 6-1mins.

39 Chapter 2. A risk assessment of Brisbane Airport habitats 25 Figure 2.1 Map showing (a) the location of the study site within Queensland; (b) the study site broken into habitat areas and Variable Circular Points in each habitat.

40 26 Chapter 2. A risk assessment of Brisbane Airport habitats Number of Aircraft Movement :-:59 1:-1:59 2:-2:59 3:-3:59 4:-4:59 5:-5:59 6:-6:59 7:-7:59 8:-8:59 9:-9:59 1:-1:59 11:-11:59 12:-12:59 13:-13:59 14:-14:59 15:-15:59 16:-16:59 17:-17:59 18:-18:59 19:-19:59 2:-2:59 21:-21:59 22:-22:59 23:-23:59 Time of Day Figure 2.2 Average number of aircraft movement over a daily period. Birds that utilised the census area for food, foraging, hunting, resting and nesting were recorded. Any birds that flew over the area (excluding birds hunting) were not included as using the area for resources. To reduce bias and to increase the precision of bird counts the same observer was used for all bird counts (Cunningham et al. 1999). Bird observations were restricted to days when weather conditions did not interfere with the detections of birds, eg rain, excess wind and fog (Ralph et al. 1993) Statistical analysis All data were entered into SPSS 11.5 for windows, and tested for normality. Transformations of log +1 were applied where necessary. 2 way ANOVAs (analysis of variance) were conducted on all data to determine the significance of bird population parameters.

41 Chapter 2. A risk assessment of Brisbane Airport habitats Results Bird numbers and distribution A total of 11 bird species were observed within the Brisbane airport boundaries (Appendix 1). The Straw necked ibis (Threskiornis spinicollis) was the most abundant species contributing 15.6% of all birds recorded. The second most abundant species was the Fairy martin (Hirundo ariel) comprising 8.7% of the total (Table 2.1) Many species were found only in specific habitats, for example: Richard s pipit (Anthus novaeseelandiae) was only observed in the managed grasslands; Mangrove gerygone (Gerygone levigaster) was only observed in mangrove forests; Rufous whistler (Pachycephala rufiventris) was found only in casuarina plantations; Lewin s rail (Rallus pectoralis) was found only in canal wetland communities; while other species such as the Australian white Ibis or Sacred ibis (Threskiornis aethiopica), Straw necked ibis and Australian kestrel (Falco cenchroides) were identified in more than a single habitat (see Appendix 1). The Torresian crow (Corvus orru) was observed in all six habitats. Of all bird numbers observed, 4% were recorded in the managed grassland, 18% were observed along the coastal dunes and foreshore, 15% were observed within the unmanaged grasslands, 13% within the casuarina plantations, 11% within the canal wetland communities, and the lowest percentage of bird species, 3%, was found in the mangrove forests (Figure 2.3).

42 28 Chapter 2. A risk assessment of Brisbane Airport habitats Table 2.1 Maximum number of each bird species recorded at Brisbane Airport; % of total number of birds for each species; % of total bird numbers for each species in each habitat. Bird Species Max count % of Total Count % bird Abundance (top 15) In each habitat Straw necked Ibis (Threskiornis spinicollis ) Fairy martin (Hirundo ariel) Golden headed cisticola (Cisticola exilis) Silver gull (Larus novaehollandiae) Tawny grassbird (Megalurus timoriensis) Red necked stint (Calidris ruficollis) Sacred Ibis-(Threskiornis aethiopica) Torresian crow (Corvus orru) Red knot (Calidris canutus) Richard s pipit (Anthus novaeseelandiae) Sharp tailed sandpiper (Calidris acuminata) Pacific black duck (Anas superciliosa) Curlew sandpiper (Calidris ferruginea) Whimbrel (Numenius phaeopus) Magpie-lark (Grallina cyanoleuca) Gull billed tern (Sterna nilotica) Welcome swallow (Hirundo neoxena) Bar tailed godwit (Limosa lapponica) Rufous whistler (Pachycephala rufiventris) Chestnut teal (Anas castanea) Common starling (Sturnus vulgaris) Varied (mangrove) honeyeater (Lichenostomus versicolor) Cattle egret (Ardea ibis) Grey fantail (Rhipidura fuliginosa) Australian magpie (Gymnorhina tibicen) Chestnut breasted mannikin (Lonchura castaneothorax) Masked lapwing (Vanellus miles) Black winged stilt (Himantopus himantopus) Mangrove gerygone (Gerygone levigaster) Eastern Curlew (Numenius madagascariensis) Red-capped plover (Charadrius ruficapillus) Pied oystercatcher (Heamatopus longirostris) Sanderling (Calidris alba) Grey shrike thrush (Colluricincla harmonica) Australian kestrel (Falco cenchroides) Red-backed fairy wren (Malurus melanocephalus) Brown quail (Coturnix pectoralis) Grey butcherbird (Cracticus torquatus) Mongolian (lesser) sand plover (Charadrius mongolus) Olive backed oriole (Oriolus sagittatus) Silver eye (Zosterops lateralis) Black shouldered kite (Elanus notatus) % 7.68% 6.57% 5.89% 5.31% 5.13% 4.91% 3.91% 3.78% 2.67% 1.8% 1.78% 1.74% 1.67% 1.66% 1.58% 1.41% 1.4% 1.38% 1.43% 1.42% 1.36% 1.15% 1.15% 1.15% 1.13%.91%.82%.78%.69%.65%.63%.61%.61%.55%.49%.45%.46%.44%.44%.42%.42% Double banded plover (Charadrius mongolus) 22.42% Collared kingfisher (Halcyon chloris) Grey tailed tattler (Tringa brevipes) Royal spoonbill (Platalea regia) Little grassbird (Megalurus gramineus) Tree martin (Hirundo nigricans) Common Sandpiper (Actitis hypoleucos) Australian pelican (Pelecanus conspicilatus) Crested pigeon (Ocyphaps lophotes) Intermediate egret (Egretta intermedia) Black faced cuckoo shrike (Coracina novaehollandiae) Black tailed godwit (Limosa limosa) White faced heron (Ardea novaehollandiae) Pied cormorant (Phalacrocorax fuscescens) Whistling kite (Haliastur sphenurus) Terek sandpiper (Tringa terek) Little black cormorant (Phalacrocorax carbo) Willy wagtail (Rhipidura leucophyrs) Lesser golden plover (Pluvialis dominica) Little egret (Egretta garzetta) Brahminy kite (Haliastur indus) Caspian tern (Hydropogne caspia) Forest kingfisher (Halcyon macleayii) Pied Butcherbird (Cracticus nigrogularis) Common greenshank (Tringa nebularia) Little Curlew (Numenius minutes) Little pied cormorant (Phalacrocorax varius) Spangled drongo (Dicrurus bracteatus) Pale headed rosella (Platycercus adscitus) Leaden flycatcher (Myiagra rubecula) Swamp harrier (Circus approximans) White-breasted sea eagle (Haliaeetus leucogaster ) Brown Honeyeater (Lichmera indistincta) Great egret (Egretta alba) Brown gerygone (Gerygone mouki) Mangrove (striated) Heron (Butorides striatus) Lewin's rail (Rallus pectoralis) Brown falcon (Falco berigora) Galah (Cacatua roseicapilla) Rainbow lorikeet (Tricholglossus haematodus) Marsh Sandpiper (Tringa stagnatilis) Striped Honeyeater (Plectorhyncha lanceolata) Noisy Miner (Manorina melanocephala) Osprey (Pandion haliaetus) Greater (large) sand plover (Charadrius leschenaultii) Brown Goshawk (Accipiter fasciatus) Dollar Bird (Eurystomus orientalis) Mistletoe bird (Dicaeum hirundinaceum) Spotted Harrier (Circus assimilis) Rainbow bee-eater (Merops ornatus) Black bittern (Ixobrychus flavicollis) Australian darter (Anhinga melangaster) White eared honeyeater (Lichenostomus leucotis) Yellow faced honeyeater (Lichenostomus chrysops) Clamorous reed warbler (Acrocephalus stentoreus) %.4%.4%.36%.29%.29%.29%.29%.27%.27%.25%.25%.23%.21%.21%.21%.21%.19%.19%.15%.15%.15%.15%.13%.11%.11%.11%.11%.1%.1%.1%.8%.8%.8%.6%.6%.6%.4%.4%.4%.4%.4%.4%.2%.2%.2%.2%.2%.2%.2%.2%.2%.2%.2% Bar shoulderd dove (Charadrius bicinctus) 1.2% Fuscous honeyeater (Lichenostomus fuscus) 1.2% Lewin s honeyeater (Meliphaga lewinii) 1.2% Kookaburra (Dacelo novaeguineae) 1.2%

43 Chapter 2. A risk assessment of Brisbane Airport habitats 29 Note (for table 2.1): 1. Managed grassland 2. Unmanaged Grassland 3. Casuarina Plantation 4. Canal Wetland Communities 5. Mangrove Forests 6. Coastal Dunes and Foreshore 3% 18% 4% Managed Grassland Unmanged Grasslands 11% Casuarina Plantations Canal Wetland Communitites 13% 15% Mangrove Forests Coastal Dunes and Foreshore Figure 2.3 Percentage of all bird numbers observed within all habitats at the Brisbane Airport Bird numbers and distribution by habitat Managed Grasslands The most numerous species found within the managed grasslands was the Straw necked ibis comprising 38.34% of all bird numbers recorded within this habitat. The Fairy martin was the next most numerous (14.21% of total bird numbers recorded) followed by the Sacred ibis making up 1.23% of individuals observed in the managed grasslands (Table 2.1).

44 3 Chapter 2. A risk assessment of Brisbane Airport habitats Unmanaged Grasslands The most abundant bird species recorded in the unmanaged grasslands was the Golden headed cisticola (Cisticola exilis) (3.27%), followed by the Tawny grassbird (Megalurus timoriensis) (2.7%). The Torresian crow was the third most numerous bird species found in this habitat (Table 2.1) Casuarina Plantations Within the casuarinas the most common species observed was the Rufous Whistler (Pachycephala rufiventris) comprising 28.63% of individuals recorded. This was followed by the grey fantail (Rhipidura fuliginosa) with 22.35%, and the Torresian crow (12.94%) (Table 2.1) Canal Freshwater Wetland, Sedge and Salt marsh Communities The most common bird species in these areas were the same as for unmanaged grasslands with the Tawny grassbird making up 39.79% of all bird species recorded and the Golden headed cisticola the second most numerous species at 3.24% (Table 2.1) Mangrove Forests The Mangrove honeyeater (Lichenostomus versicolor) was the most common bird species (31.94%) while the Mangrove gerygone was the next most common in this habitat type (19.44%) (Table 2.1) Coastal Dunes and Foreshore The most abundant species found within the coastal area was the Silver Gull (Larus novaehollandiae), comprising 17.45% of all birds recorded. The red

45 Chapter 2. A risk assessment of Brisbane Airport habitats 31 necked stint (Calidris ruficollis) was the second most numerous in this habitat (14.32%) (Table 2.1) Species richness Bird diversity was high in all habitats, with the coastal dunes and foreshore and the managed grasslands sharing the greatest overall species richness (Figure 2.4). Species richness also varied temporally with the managed grasslands and the coastal dunes and foreshore consistently having the greatest number of species across the year. (Table 2.2) Number of species in each habitat was assessed seasonally, showing that managed grasslands, coastal dunes and foreshore shared the greatest species richness across all seasons (Figure 2.5).

46 32 Chapter 2. A risk assessment of Brisbane Airport habitats Number of Species Managed Grasslands Unmanaged Grasslands Casuarina Plantations Canal Wetland Communities Mangrove Forests Coastal Dunes and Foreshore Habitat Figure 2.4 Number of bird species found in habitats at the Brisbane Airport Table 2.2 Numbers of bird species observed in each habitat over a yearly period JUL 23 AUG 23 SEP 23 OCT 23 NOV 23 DEC 23 JAN 24 FEB 24 MAR 24 APR 24 MAY 24 Managed Grasslands Unmanaged Grasslands Casuarina Plantation JUN 24 Canal Wetland Communities Mangrove Forests Coastal Dunes and Foreshore

47 Chapter 2. A risk assessment of Brisbane Airport habitats 33 Average Number of Species Managed Grasslands Unmanaged Grasslands Casuarina Plantations Canal Wetland Communities Mangrove Forests Coastal Dunes and Foreshore Summer Autumn Winter Spring Habitat Figure 2.5 Average seasonal species richness for each habitat at the Brisbane Airport Monthly and seasonal bird distribution across habitats A significant difference was observed in the total abundance of birds present among each habitat type (2 way ANOVA, d.f. =5,21; F=21.43; p=.) with the managed grasslands and the coastal dunes and foreshore having significantly higher abundance of birds compared with other habitats (Figure 2.6). No significant difference was observed in abundance of birds found in all habitats over the length of a year. (2 way ANOVA d.f. = 11,24; F=.456; p=.928) (Figure 2.7 a, b, c, d, e, f) A significant difference was also observed in bird abundance across seasons however, with managed grasslands showing a greater abundance of birds during the winter months; coastal dunes and foreshore showing the greatest abundance of birds in the spring, summer and autumn months compared

48 34 Chapter 2. A risk assessment of Brisbane Airport habitats with other habitats. (Figure 2.8) 1 8 Bird Numbers Managed Grasslands Casuarinas Mangroves Unmanaged Grasslands Canal Wetlands Foreshore Habitat Figure 2.6 Difference in number of birds per hectare observed in all habitats at the Brisbane Airport. (Mean ± SE)

49 Chapter 2. A risk assessment of Brisbane Airport habitats 35 5 a. Managed Grasslands b. Unmanaged Grasslands Bird numbers Bird numbers Jul 23 Aug 23 Sep 23 Oct 23 Nov 23 Dec 23 Jan 24 Feb 24 Mar 24 Apr 24 May 24 Jun 24-6 Jul 23 Aug 23 Sep 23 Oct 23 Nov 23 Dec 23 Jan 24 Feb 24 Mar 24 Apr 24 May 24 Jun 24 Month Month 2 c. Casuarina Plantations d. Canal Wetland Communities 1 8 Bird numbers 1 Bird numbers Jul 23 Aug 23 Sep 23 Oct 23 Nov 23 Dec 23 Jan 24 Feb 24 Mar 24 Apr 24 May 24 Jun 24-6 Jul 23 Aug 23 Sep 23 Oct 23 Nov 23 Dec 23 Jan 24 Feb 24 Mar 24 Apr 24 May 24 Jun 24 Month Month 2 e. Mangrove Forests f. Coastal Dunes and Foreshore 2 Bird numbers 1 Bird numbers Jul 23 Aug 23 Sep 23 Oct 23 Nov 23 Dec 23 Jan 24 Feb 24 Mar 24 Apr 24 May 24 Jun 24-2 Jul 23 Aug 23 Sep 23 Oct 23 Nov 23 Dec 23 Jan 24 Feb 24 Mar 24 Apr 24 May 24 Jun 24 Month Month Figure 2.7 Yearly bird abundance in each habitat at the Brisbane Airport (Mean ± SE)

50 36 Chapter 2. A risk assessment of Brisbane Airport habitats 3 Birds/hectare/hour Winter Spring Summer Autumn Managed Grasslands Unmanaged Grasslands Casuarina Plantations Canal Wetland Communities Mangrove Forests Coastal Dunes and Foreshore Habitat Figure 2.8 Seasonal bird abundance in each habitat at the Brisbane Airport Daily bird abundance A significant difference was observed in the number of birds present at different periods of the day with more birds per hectare (2 way ANOVA, d.f. = 2,213; F=11.912; p=.), and larger numbers per ten minutes of observation time, seen during the first three hours of sunlight (2 way ANOVA d.f. =2,213; F=8.367; p<.5.) (Figure 2.9 a, b)

51 Chapter 2. A risk assessment of Brisbane Airport habitats a Birds per Hectare b. 3 Hrs After Sunrise 3 Hrs over Midday Time of Day 3 Hrs before Sunset 5 Bird Numbers Hrs After Sunrise 3 Hrs over Midday 3 Hrs before Sunset Time of Day Figure 2.9 Difference in bird numbers observed during three periods of the day; a) Number of Birds per hectare; b) Number of birds/ten minutes (Mean ± SE)

52 38 Chapter 2. A risk assessment of Brisbane Airport habitats 2.5 Discussion A total of 11 bird species were recorded at Brisbane airport during the census period. This number is slightly lower than had been reported in previous surveys that have been conducted at Brisbane airport, e.g. the Fauna Report, conducted by Lambert and Rehbien in The difference probably reflects differences in the methodology employed with only birds that spent time within airport habitats recorded here. Incidental sightings of bird species were not included here as they were unlikely to contribute to an ongoing hazard. Bird diversity was high in all habitats although not all species can be considered to be a risk to aircraft. Many species found in the unmanaged grasslands (eg. Tawny grassbird, Golden headed cisticola); the canal wetlands (eg. Silver eye - Zosterops lateralis, Chestnut breasted mannikin - Lonchura castaneothorax); the casuarina plantations (eg. Rufous whistler, Olive backed oriole - Oriolus sagittatus) and the mangrove forests (eg. Grey shrike thrush - Colluricincla harmonica, Mangrove honeyeater - Lichenostomus versicolor) have not been reported to have been involved in bird-aircraft collisions at Brisbane airport. They are not currently considered to be hazardous species as their behaviour does not bring them into the vicinity of aircraft flight paths. Results of this study show clearly that managed grasslands around the runways, taxiways and aprons provide suitable habitat for a large range of bird species. 4 percent of all bird species observed in the study were recorded in grasslands exhibiting a diverse range of behaviours including foraging, hunting and roosting. In addition to largest abundance, the managed grasslands also showed a high species richness. Thus more bird species were present in managed grasslands per hectare compared with other habitats except for the coastal dunes and foreshore.

53 Chapter 2. A risk assessment of Brisbane Airport habitats 39 Although the coastal dunes and foreshore showed a greater diversity of species, many were only present during the spring and summer months, and so probably constitute migratory species that spend their spring and summer period feeding in Moreton Bay. Migratory wader species are not considered to be a great risk to aircraft at Brisbane airport. Previous bird strike data show only two instances of bird strike where a tern or sandpiper species was involved (these instances were not identified to species and so we cannot be certain that they were indeed migratory species) and there has been one instance of a strike with a migratory Red-necked stint (Calidris ruficollis). Fluctuations in bird numbers across the year were not large, even taking into consideration changes in migratory wader numbers. Thus the majority of birds observed in any single month were likely to be residents of an area and therefore to be ongoing users of resources found in the habitats in which they were observed. Bird numbers and hence activity levels were highest in the early morning hours. This has a bearing on the risk attached to many bird species as the number of aircraft movements is also high during this time period. The number of aircraft movements is greatest in early morning followed by the midday and early evening hours (Fig 2.2). Although activity of all bird species was highest during the early morning, many species may not pose hazards to aircraft. A bird species hazard index is required therefore, before assigning relative risk to particular times of the day. This study shows clearly that managed grasslands support the greatest abundance of bird numbers and species. Further analysis here therefore should focus on determining which bird species pose potential hazards in relation to birdstrikes. Subsequently the habitat(s) that contain the greatest abundance and diversity of potentially hazardous birds over time need to be identified.

54 4 Chapter 3. Hazard index for Brisbane Airport habitats 3. A bird hazard index for operational and surrounding habitats of Brisbane airport 3.1 Introduction Most airports need to reduce the risk of bird strikes in and around the airport environment. This is usually carried out by performing risk assessments that identify areas and habitats where major bird hazards occur. Management can then be concentrated on these areas and control applied to reduce costs of management and to increase saftey levels. Identifying where hazards can be found in the airport environment is only the first step to correctly identifying where effort to reduce risk should be concentrated. When directing effort to reduce bird strike potential at airports, many different issues need to be considered. All bird species may pose a risk to aircraft, but not all species may be equally hazardous. Factors such as species, density, location and individual species behaviour need to be taken into account before determining the relative threat individual species pose to aircraft (Allen 2). As noted earlier, larger and heavier birds are greater potential hazards to aircraft because they can cause more damage compared with smaller, lighter birds (Milsom 199). It is also accepted that the higher the relative bird density, the greater will be the hazard to aircraft (Sodhi 22). An index for bird hazards at the Brisbane aiport should be based on weight and number of hazardous birds that are present within and surrounding the airport environments. In order to establish which habitat(s) at the Brisbane airport contain the greatest number of potentially hazardous birds, an assessment of previous

55 Chapter 3. Hazard index for Brisbane Airport habitats 41 bird strike data and bird presence at Brisbane airport is required to identify areas that offer the greatest potential for bird strikes. A bird strike reporting system operates at Brisbane airport, that not only reports strikes noticed by security staff or aircraft staff, but includes reports from ground staff when unexplained bird remains are found on, or surrounding, runways and taxiways. This bird strike data set will be used here to determine which bird species pose threats to aircraft at the Brisbane airport. Once specific hazardous species have been identified, this can be combined with data presented earlier to identify areas that contain the greatest numbers of these species. In order to allow monitoring and comparison in further years, all hazardous species will be indentified, and then the top ten hazardous species (based on weight and numbers) will be the major focus. This will enable effort to be directed at reducing bird strike potential according to a weighted scale from greatest to least hazard potential for both bird species and habitat type. 3.2 Aims (1) To assess previous bird strike data to determine bird species that pose the greatest hazard to aircraft at Brisbane airport and to develop a bird hazard index focusing on species that are of greatest concern at Brisbane airport. (2) To identify habitat types at Brisbane airport that contain the greatest abundance of hazardous bird species. (3) To provide recommendations for new scientifically based management options for areas that contain the greatest bird hazard to aircraft.

56 42 Chapter 3. Hazard index for Brisbane Airport habitats 3.3 Methods Study area For a description of the study area please see section Habitat description See Section 2.3 for description of habitats Hazard ranking data compilation Hazard ranking of bird species found at the Brisbane Airport was based on previous bird strike data (BAC pers comm.) and combined weights of all birds involved in aircraft collisions (Searing 21). The mean weight of all bird species observed, were obtained from Dunning (1992), or an average of male and female weight were taken if separate weight estimates were provided for individual sexes of a certain species. If bird strike data were not specific and reports only cited to family, then the average weight of all birds observed in that family was used. For bird species that were not identified an average weight of all birds involved in aircraft strikes for the same month at the Brisbane Airport was used.

57 Chapter 3. Hazard index for Brisbane Airport habitats Results Hazardous bird presence at Brisbane airport Hazardous bird species were determined from previous bird strike data collected between 1996 and 23 (BAC Database). All bird species previously involved in aircraft collisions were identified as a potentially hazardous species. Of the 11 species identified as using the entire Brisbane airport on a regular basis (Appendix 1), 37 individual species were classed as hazardous to aircraft based on bird strike data records for the Brisbane airport from These species were grouped into family or left as individual species, depending on the specificity of bird strike data. Each species was given a hazard ranking based on a: the weight of each species involved in aircraft strikes and b: the total number of each species previously involved in aircraft collisions. Table 3.1 identifies bird species that have been involved in aircraft collisions from and also those responsible for bird strikes in 23 alone, and their relative hazard rating. Note that unidentified (unknown) bird species that have been involved in aircraft strikes have also been given a hazard rating but were disregarded for the top ten specific hazardous bird species rankings Monthly and seasonal hazardous bird abundance and distribution Managed grasslands contained the greatest number of hazardous birds with mangrove forests having the lowest abundance. (Figure 3.1) Number of hazardous birds observed in each habitat type differed significantly (F=62.863; d.f. =5, 21; p=.) with managed grasslands having the greatest number followed by the coastal dunes and foreshore. Other habitats were not significantly different from each other (Figure 3.2).

58 44 Chapter 3. Hazard index for Brisbane Airport habitats Table 3.1 Bird strike data, weights and hazard ranking for bird species found at the Brisbane Airport Species Strikes 23 Weight g Strikes Weight g Hazard Ranking A Hazard Ranking B Nankeen Kestrel Lapwing Spp Swallow Spp/ Martin Spp Egret Spp Torresian Crow Duck Spp Other Raptor Spp Bittern Spp Heron Spp Pigeon Spp Sparrow Spp Royal Spoonbill Common Starling Tern Spp Ibis Spp Magpie Lark White Breasted Sea Eagle Australian Magpie Cormorant Spp Goose Spp Finch Spp Gull Spp Galah Owl Spp Rainbow Lorikeet Red -Necked Stint Sandpiper Spp Unknown Strikes By Other Animal Spp N/A N/A N/A N/A Note (Table 3.1) A. Hazard ranking by weights of birds struck B. Hazard ranking by number of Birds Struck 22% % 5% 8% 3% 62% Managed Grasslands Unmanaged Grasslands Casuarina Plantations Canal Wetland Communities Mangrove Forests Coastal Dunes and Foreshore Figure 3.1 Percentage of hazardous birds observed in all habitats on and around the Brisbane Airport

59 Chapter 3. Hazard index for Brisbane Airport habitats 45 1 Birds numbers per hectare Managed Grasslands Casuarina Plantations Mangroves Unmanaged Grasslands Canal Wetlands Foreshore Habitat Figure 3.2 Hazardous birds observed in each habitat at the Brisbane Airport: (Mean ± SE) No significant difference was observed in the total number of hazardous birds (2 way ANOVA F=.565; d.f. =2, 24; p=.856) and the number of birds per hectare (2 way ANOVA F=.277; d.f. = 2,24; p=.99) observed during each month of the year (Figure 3.3). When bird numbers were averaged over seasons, the managed grassland showed a greater abundance of hazardous birds across all four seasons (Figure 3.4).

60 46 Chapter 3. Hazard index for Brisbane Airport habitats Daily hazardous bird abundance Time of day did not have a significant effect on the number of hazardous bird species observed at the Brisbane Airport. (2 way ANOVA F=2.54; d.f. =2, 213; p=.84)(figure 3.5) Top ten hazardous bird species and distribution In order to focus control and/or management options to reduce the bird strike hazard at Brisbane airport, we focussed on the top ten ranked hazardous bird species (Table 3.1). These top ten ranked hazardous species were all found in a variety of habitats (Figure 3.6). (NB the unknown species that ranked one for number struck and two for weight of birds struck were not taken into account for the hazardous species, as the focus needed to be on known species in order to develop management options). Ibis, kestrel, lapwing and egret species were more abundant in managed grasslands; sea eagles and other raptor species utilised the canal wetland communities more extensively than other habitats, while coastal dunes and foreshore had the greatest abundance of heron, duck and cormorant species. The final hazardous species, Torresian crow, was recorded in all habitats although the greatest numbers were observed in the casuarina plantations. NB. The goose was omitted from the final hazardous species list because during the bird census, there was no record of a goose species utilising airport habitats.

61 Chapter 3. Hazard index for Brisbane Airport habitats 47 a. 1 Bird Numbers per hectare Jun 4 May 4 Apr 4 Mar 4 Feb 4 Jan 4 Dec 3 Nov 3 Oct 3 Sep 3 Aug 3 Jul 3 Month Figure 3.3 Number of hazardous birds observed over a yearly period at the Brisbane Airport: Number of birds per hectare (Mean ± SE)

62 48 Chapter 3. Hazard index for Brisbane Airport habitats 35 3 Bird Numbers Summer Autumn Winter Spring Managed Grasslands Unmanaged Grasslands Casuarina Plantations Canal Wetland Communities Mangrove Forests Coastal Dunes and Foreshore Habitat Figure 3.4 Average seasonal hazardous bird abundances for each habitat at the Brisbane Airport. 4 Birds Observed Hrs After Sunrise 3 Hrs Over Midday 3 Hrs Before Sunset Time of Day Figure 3.5 Number of hazardous birds observed during the day. (Mean ± SE)

63 Chapter 3. Hazard index for Brisbane Airport habitats 49 a. Ibis Sp Birds/Hectare/Hour Managed Grasslands Canal Wetland Communities Mangrove Forests Coastal Dunes and Foreshore b. Birds/Hectare/Hour Managed Grasslands Kestrel Unmanaged Grassslands Canal Wetland Communities c. Sea Eagle d. Raptor sp Birds/Hectare/Hour Casuarina Plantations Canal Wetland Communities Coastal Dunes and Foreshore Birds/Hectare/Hour Managed Grasslands Unmanaged Grassslands Canal Wetland Communities Coastal Dunes and Foreshore e. Lapw ing Sp f. Egret sp Birds/Hectare/Hour Managed Grasslands Coastal Dunes and Foreshore Birds/Hectare/Hour Managed Grasslands Unmanaged Grassslands Canal Wetland Communities Mangrove Forests Coastal Dunes and Foreshore g. Heron sp h. Duck sp Birds/Hectare/Hour Managed Grasslands Mangrove Forests Coastal Dunes and Foreshore Birds/Hectare/Hour Managed Grasslands Unmanaged Grassslands Mangrove Forests Coastal Dunes and Foreshore i. Cormorant sp j. Torresian Crow Birds/Hectare/Hour Coastal Dunes and Foreshore Birds/Hectare/Hour Managed Grasslands Unmanaged Grassslands Casuarina Plantations Canal Wetland Communities Mangrove Forests Coastal Dunes and Foreshore Figure 3.6 Top ten hazardous bird species (based on weight) and habitats in which they are found at the Brisbane Airport.

64 5 Chapter 3. Hazard index for Brisbane Airport habitats 3.5 Discussion Results of the study show clearly that managed grasslands around the runways, taxiways and aprons provide suitable habitat for a great range of bird species. 4 percent of all bird numbers (from all habitats) observed in the study were recorded in managed grasslands (see Chapter 2) and exhibited a diverse range of behaviours including foraging, hunting and roosting. Of the species recorded in managed grasslands, 62 percent of these species were deemed to be hazardous or to pose a potential risk to aircraft based on previous bird strike data Hazardous bird presence at the Brisbane airport Bird diversity was high in all habitats (see Chapter 2), although not all species were considered to be a risk to aircraft. Many species found in the unmanaged grasslands, the canal wetlands, the casuarina plantations and the mangrove forests are not known to have been involved in bird-aircraft collisions at Brisbane airport and are therefore not considered currently to be hazardous species. Based on previous bird strike data the top ten bird species that pose the greatest risk to aircraft are listed in table 3.1. Potential for a catastrophic bird strike rises with individual size/weight and number of birds struck. The larger and heavier the bird and the greater number of birds struck in one instance, the greater is the hazard of damage (Milsom 199) or abortion of take off and hence loss of capital. Previous bird strike data at the Brisbane airport has shown that the majority of bird strikes have involved only a single individual (87% pers comm BAC). It is because of these facts that estimates of bird risk at Brisbane airport have been based, in the first instance, on size and weight of individual bird species, and secondly on their relative abundance.

65 Chapter 3. Hazard index for Brisbane Airport habitats 51 Ranking of known hazardous bird species, identified Ibis as the greatest risk to aircraft at Brisbane airport. Ibis utilise grassland around the runways, taxiways and aprons more extensively and in greater numbers than any other habitat within the airport boundaries. The fact that ibis also congregate in relatively large numbers makes their hazard potential far greater than bird species that do not flock to the same extent. Austalian kestrels pose the second greatest hazard at Brisbane airport. This species has been involved in the most aircraft strikes at Brisbane airport but is ranked second most hazardous because it weighs significantly less than ibis. Kestrels were also seen in greatest numbers in the managed grasslands but also occur in unmanaged grasslands and canal wetland communities to a lesser extent. Based solely on individual weight of bird species colliding with aircraft, the White breasted sea eagle poses the greatest potentail damage hazard to aircraft. This species however has been involved in aircraft strikes only six times between White breasted sea eagles utilise the canal wetland communities far more extensively than any other habitat. During the point counts, a white breasted sea eagle nesting site was discovered at the airport that appears to be reused every year for rearing juveniles. Removal of the nest should reduce the threat posed by this species. Other raptor species were ranked fourth greatest hazard risk to aircraft, they were generally observed in greater numbers in the canal wetland communities. Raptors may use this area for foraging and hunting over the rank grasslands. Some raptor species were also observed nesting within eucalypts adjacent to airport boundaries. In order to reduce raptor numbers, nesting opportunities need to be reduced where possible.

66 52 Chapter 3. Hazard index for Brisbane Airport habitats Other species that have been involved in aircraft strikes, (Lapwing and Egret species) were observed in greatest numbers in the managed grasslands. The most common behaviour observed was that of foraging, feeding and breeding (in the case of the lapwings), indicating that these areas may afford greater prey availability and other prefered habitat requirements than alternative habitats around the airport. Heron, duck and cormorant species were observed in greatest abundance in the coastal dunes and foreshore areas. Involvement of these species in aircraft strikes may result from them utilising airport airspace simply as a transit route from one preferred area to another. In order to reduce the likelihood of a strike, bird hazing tactics (scaring) that are used at Brisbane airport should be kept in place to deter these species. The Torresian crow, although at the lower end of the hazard scale, is the one species observed in all habitats within the airport boundaries. Reducing the numbers of this species may require more than habitat manipulation or removal of observed attractants. Crows utilise the casuarina plantations for a variety of behaviours, mostly perching and resting within the tops of the casuarinas, but were rarely seen there foraging or feeding. So while casuarinas are considered to be a poor fauna habitat for most species, they still appear to supply a vital resting area for the tenth most hazardous species of bird (Torresian crow) at Brisbane airport. In order to reduce the abundance of Torresian crows, deterrent techniques should be implemented Monthly and seasonal abundance of hazardous birds at Brisbane airport Data showed that relative abundance of hazardous bird species remained basically constant across the year. When each habitat type was analysed separately, managed grasslands showed the greatest abundance of

67 Chapter 3. Hazard index for Brisbane Airport habitats 53 hazardous species during the winter months (June, July and August) and the lowest presence of hazardous bird species during the summer period (December, January and February). Management and control of hazardous species will thus require greater effort to be employed during the winter months within the managed grasslands at Brisbane airport. Coastal dunes and the foreshore showed the greatest abundance of potentially hazardous species during the autumn months (March, April and May). This is most likely due to the appearance of migratory wader species using the area for feeding before migration to breeding grounds during the winter period. Other habitats within the airport boundaries did not show great variation in hazard potential across seasons. While total bird abundance did vary across the day as a whole (See chapter 2), abundance of hazardous birds was constant. Thus bird control efforts directed against hazardous species need to be maintained throughout the whole day, not just during peak activity periods for birds or aircraft movements Limitations on hazard ranking A large number of bird strikes at Brisbane airport have occurred without records having been made of the actual species involved. When bird weights are averaged the hazard index of these unknown strikes is relatively high (Rank 2, see table 3.1). In order to properly rank these strikes and to determine their potential hazard, greater effort needs to be directed at correct identification of bird species involved in strikes in the future. This may be done by sending remains of unidentified birds to specialists, in order to have them properly identified. Larger bird species involved in strikes have a greater chance of being noticed and reported, whereas strikes involving smaller birds, that may not inflict any damage to the aircraft often

68 54 Chapter 3. Hazard index for Brisbane Airport habitats go unnoticed or are not reported. Consistent and correct reporting of all birdstrikes must be instigated if efforts to reduce bird strike risk are to be effective in the future Habitat hazard ranking and bird reduction recommendations Hazard rank 1 - Managed grasslands Managed grasslands around the taxiways and aprons contain the greatest abundance of bird species, both in number and hazard potential to aircraft and should be the area where the greatest control and hazard reduction activities should be focused. The management of these grasslands will be addressed later (Chapter 4) Hazard rank 2 - Coastal dunes and foreshore Although the coastal dunes and foreshore provide many requirements for most hazardous bird species, no major manipulation of the dunes or mudflats is planned and techniques to deter bird species from utilising the airport as a movement corridor between habitats need to be investigated and employed. Reduction of perching opportunities (eg. emergent trees) for bird species should be undertaken. Management of the stretch of grassland along the foreshore will be addressed later (Chapter 4).

69 Chapter 3. Hazard index for Brisbane Airport habitats Hazard rank 3 - Casuarina plantations These areas provide poor habitat requirements for the majority of hazardous bird species. The Torresian crow and the White breasted sea eagle were the only two hazardous bird species that utilised these areas regularly. Reduction in White breasted sea eagle numbers may be achieved by monitoring this species and investigating options for either reducing nesting opportunities or relocating existing nesting areas within the airport boundaries. The Torresian crow utilises casuarina plantations extensively, but even the removal of these areas (for example when construction of the new runway begins) will not necessarily reduce their numbers as they have been observed to utilise all available habitats at the airport. To reduce abundance of crows hazing of this species should be increased, and new options for deterring this species should be trialed Hazard rank 4 - Canal freshwater wetland, sedge and salt marsh communities The canal freshwater wetland, sedge and salt marsh communities are similar to those of the unmanaged grasslands within the operational areas of the airport, and these areas provide hunting and roosting opportunities for many hazardous bird species. These areas should also be managed to reduce habitat requirements for hazardous species. Uunmanaged grasslands were the focus of habitat manipulation experiments in Chapter 4 so recommendations

70 56 Chapter 3. Hazard index for Brisbane Airport habitats for bird control effort in these areas will be discussed later Hazard rank 5 - Unmanaged grasslands Although unmanaged grasslands provide few of the basic habitat requirements for hazardous bird species in the original bird risk assessment, they were involved in the experiments currently being undertaken on the managed grasslands, and recommendations for control of these areas will be discussed in Chapter Hazard rank 6 - Mangrove forests Hazardous bird species were low within mangrove forests and no manipulation or bird reduction efforts is considered necessary in these habitats, currently Other recommendations In order to increase the accuracy of bird species hazard ranking and to provide a more detailed bird strike data base, records of bird strikes must correctly identify all individual birds involved in aircraft collisions.

71 Chapter 4. Grassland management strategy to reduce bird strikes A cost effective grassland management strategy to reduce the number of bird strikes at Brisbane airport 4.1 Introduction Bird strikes are an escalating problem at many airports, so much so that bird species, their abundance and activity around airports are a major focus when assessing risk to aircraft movements (Allen 2; Allen et al. 23). Habitat management achieved by modification of vegetation present within airport boundaries combined with use of bird dispersal techniques have been regarded as some of the most effective long term management options for reducing bird numbers at airports. (Solman 1969; Burger 1983; Buckley & McCarthy 1994; Brown et al. 21; Byron & Downs 22) Studies into the effectiveness of maintaining long grass as a bird deterrent have demonstrated that grass heights between 15 and 45 cm can deter bird species such as gulls and lapwings (Brough & Bridgman 198; Buckley & McCarthy 1994) while this approach is not as effective for other species such as Canadian geese (Seamans & Dolbeer 1999). While many airports have adopted a long grass policy as a part of their ongoing bird strike risk management, this option must be tailored to each specific location to account for difference in bird species, vegetation types, food resource availability and local environmental conditions. A previous bird risk assessment undertaken at Brisbane airport (Chapter 3) has identified Ibis (Threskiornis aethiopica and T. spinicollis), the Australian kestrel (Falco cenchroides), raptor species (Black shouldered kite Elanus axillaris, Whistling kite Haliastur sphenurus, White breasted sea eagle (Haliaeetus leucogaster), Masked lapwing (Vanellus miles) and Egret species

72 58 Chapter 4. Grassland management strategy to reduce bird strikes (Great egret Egretta alba, Intermediate egret Egretta intermedia, Little egret Egretta garzetta and Cattle egret Ardea ibis) to be the major bird threats to aircraft safety. Chapter 2 and 3 of this study identified managed grasslands as the habitat providing greatest threat of birdstrike at Brisbane airport. The objective of this study was to develop a cost effective and environmentally acceptable grass height management strategy that can be applied to the managed grasslands of the Brisbane airport to reduce potential hazard of bird strikes. 4.2 Methods Study area See Section All sites for grassland manipulation trials were chosen within maintained areas, and grass left to grow for three months prior to the study. Three geographically separate areas ranging from 7.7 hectares in area 1, 14.3 hectares in area 2 and 11. hectares in area 3, were chosen for the study (Figure 4.1a) Prior to Manipulation Vegetation structure The areas selected for this study were chosen in locations that had been analysed previously for vegetation diversity in a flora and fauna survey (ERM

73 Chapter 4. Grassland management strategy to reduce bird strikes 59 a. b. c. d. Figure 4.1 a) Grassland management study areas within Brisbane Airport Boundaries. b) Site A. c) Site B. d) Site C. (Each site broken into 4 areas of equal size and randomly allocated a treatment height)