7.7 Species Habitat Model for Bald Eagle

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1 7.7 Species Habitat Model for Bald Eagle Common Name: Bald Eagle Scientific Name: Haliaeetus leucocephalus Species Code: B-BAEA B.C. Status: Yellow-listed Identified Wildlife Status: None COSEWIC Status: Has not been examined Introduction General habitat ratings for the Bald Eagle are predicted to have a low reliability as no model verification has been done, and there is very little documented of the wildlife and habitat associations for this area of British Columbia. Trees used for Bald Eagle nesting and important food sources in this area of northeastern B.C. are not known (Blood and Anweiler, 1994). The information presented in the species-habitat model has largely been extrapolated from other regions and has not been validated for the study area. As information is very limited on this species within northeastern British Columbia, relevant literature from B.C. and western north America has been included where applicable Distribution Provincial Range An estimated 21,000 Bald Eagles nest within British Columbia occurring over the entire province with the exception of the alpine and sub-alpine zones (Blood and Anweiler, 1994). An estimated 20,000 to 30,000 Bald Eagles winter within the province with over 90% of these birds wintering on the coast (Blood and Anweiler, 1994). The relative provincial importance of the Taiga Plains eco-province has been estimated in terms of providing Bald Eagle habitat. Within this eco-province, the BWBS biogeoclimatic zone received a rank of low to no importance for nesting habitat and a rank of no importance for winter habitat value (Blood and Anweiler, 1994). The Bald Eagle is a summer visitor to the area and scattered breeding may occur on the larger rivers within the study area. During field work, no nests were observed but a few individual birds were seen on the Liard and Beaver rivers on different occasions, generally perching in large balsam poplars. M. Labine (personal communication) in the Fort Liard area of the Northwest Territories has seen Bald Eagles mainly in the spring and the fall feeding on winter-killed ungulates in the spring. No winter use is expected Elevational Range Bald Eagles may nest up to 1370 m elevation (Campbell et al., 1990), although, they generally nest at low elevations (Blood and Anweiler, 1994).

2 7.7.3 Habitat Use (Life Requisites and Seasons) Living Bald Eagles are primarily associated with aquatic habitats and large trees. In the British Columbia Interior, important nesting habitat occurs along medium to large rivers with a low-gradient and extensive floodplain/wetland development, around wetland complexes (Blood and Anweiler, 1994), on lake shores, and on islands in rivers and lakes (Campbell et al., 1990). Bald Eagles will usually nest within 200 m of water (Gerrard et al., 1975) and rarely nest farther than a few hundred metres from shore in wilderness areas; although, in areas of human disturbance, eagles will nest farther away from water; few nests are located more than 1.6 km from permanent water (Blood and Anweiler, 1994; Anthony et al., 1982; Anthony and Isaacs, 1989). Bald Eagles are not known to occupy areas with less than 0.8 square km of open water (Peterson, 1986). Bald Eagles may nest up to 1370 m elevation (Campbell et al., 1990), although, they generally nest at low elevations (Blood and Anweiler, 1994). Generally, Bald Eagles are selecting areas for nesting with suitable forest structure, low human disturbance, and high diversity or accessibility to prey species (Livingstone et al., 1990) Feeding Bald Eagles are opportunistic feeders having a diverse diet including mainly birds (mostly water birds), fish, and carrion (Blood and Anweiler, 1994). Bald Eagles will congregate in large numbers to take advantage of locally or seasonally abundant foods (Blood and Anweiler, 1994). Important food sources within the Taiga Plains ecoprovince are not known (Blood and Anweiler, 1994). Bald Eagles will likely hunt in the recent clearcuts, wetlands, floodplains, and main rivers of the study areas Reproduction (Nesting) Nesting may occur in a variety of stand types including coniferous, deciduous, or mixed stands (Blood and Anweiler, 1994). Tree structure may be more important than tree species in determining Bald Eagle nest site selection (Gerrard et al., 1975; Anthony et al., 1982). Large, usually old-growth, prominent trees, live or dead, are needed to support their massive nests. In the B.C. Interior, most eagles nesting along rivers use cottonwoods while those in upland areas around lakes tend to use Douglas-firs or aspens (Blood and Anweiler, 1994). Important nest trees within the Taiga Plains eco-province have not yet been identified (Blood and Anweiler, 1994). M. Labine (personal communication) has seen a few birds nesting in big balsam poplars along the Liard River, Northwest Territories Spatial Requirements for Nesting Nests are rarely farther than a few hundred metres from shore in wilderness areas; although, in areas of human disturbance, eagles will nest farther away from water; few nests are located more than 1.6 km from permanent water (Blood and Anweiler, 1994; Anthony et al., 1982; Anthony and Isaacs, 1989) Breeding Season Within British Columbia, the Bald Eagle breeding season extends from mid-february to the end of August (Campbell et al., 1990). In the southern Interior, egg-laying begins in late-march to early April and begins even later in the northern Interior (Blood and Anweiler, 1994). One to three chicks hatch (average clutch size of 2) after an estimated 33 to 40 day incubation period and remain in the nest for an average of 10 to 11 weeks (Blood and Anweiler, 1994). Young may fledge from late June to late August depending on location (Blood and Anweiler, 1994). For this model, the breeding season is estimated as late March to August. Table 28: Seasons of Use With Rated Life Requisites for Bald Eagle in the La Biche and Sandy Creek Study Areas. Month Season* Rated Life Requisites January W NA February W NA

3 March W RP-SH April W RP-SH May G RP-SH June G RP-SH July G RP-SH August G RP-SH September G NA October W NA November W NA December W NA * as defined in RIC (1997a). The breeding season as defined in Table 28 is rated for security habitat (SH) values required for reproducing by eggs. Ecosystem units will not be rated for the winter season as no winter use is expected in the study areas (NA - not applicable) Ratings Rating Scheme 4 Class, 1 Season A 4-Class rating scheme of high (H), moderate (M), low (L), and nil (N) is employed due to the intermediate level of knowledge on habitat use of Bald Eagles (Resources Inventory Committee, 1997a). The used ratings scheme is defined in Table 29. Table 29: Relative Quality Classes (from RIC, 1997a and RIC, 1997g). Code Quality relative to the best in B.C. Suitability/Capability H Equivalent (75%-100% of best) High M Slightly-moderately less (25%-75% of best) Moderate L Substantially less (5%-25% of best) Low N Much less (0%-5% of best) Nil One season (Breeding) will be rated for the Bald Eagle Provincial Benchmark A Provincial Benchmark has not yet been established for the Bald Eagle. Blood and Anweiler (1994) gave habitats within the Georgia Depression and Coast and Mountains Eco-provinces the highest ratings for habitat importance for both the nesting and winter seasons within British Columbia. The Taiga Plains eco-province received a rank of low to no importance for nesting habitat and a rank of no importance for winter habitat value (Blood and Anweiler, 1994). Therefore, Class 1 habitat is not expected within the La Biche and Sandy Creek areas for Bald Eagles Assumptions Habitat ratings for the Bald Eagle is presented in sections and Nesting habitat ratings for the breeding season are Bald Eagle nesting habitat may not be strongly linked to ecosystem units, yet some site series may more reliably provide suitable trees and stand characteristics favourable for nesting. Further study is needed to validate and refine these ratings. The following assumptions have been made: Only forested units are rated due to the rarity of Bald Eagles nesting on the ground or on cliffs. Non-forested and non-and-sparsely vegetated units are assumed to have no nesting value and are therefore given nil value in the ratings table. Structural stages 1-5 have no nesting value as trees are not large enough to support the weight and structure of Bald Eagle nests. Second-growth forest with a remnant old-growth component can have some value for nesting if suitable old-growth nest trees remain. Mature and old-growth structural stages (6-7) provide the most suitable nest trees. Stage 7 has higher value than stage 6 due to presence of more prominent trees, more trees with broken tops, and a more open forest structure. Due

4 to their large wing span, Bald Eagles are more or less restricted to using the largest trees along the forest edge or dominant trees protruding above the canopy (Blood and Anweiler, 1994). Super-dominant trees are important to provide not only a suitable structure for nests but also prominent perching sites from which to watch for prey or intruders (Livingstone et al., 1990). Within the study areas, balsam poplar and aspen are the most important nest tree species. They generally have sturdier branches, attain greater size, and have more structure than spruces. Within the study areas, balsam poplar and aspen generally reach the greatest size and are found in largely riparian habitats. Therefore, units with high proportions of these tree species in the later structural stages are assigned higher nesting values. White spruce also reach a large size along the major rivers and may provide some moderate nesting values. Large diameter trees are generally required for nesting. Trees with a DBH of less than 76 cm are rarely used (Blood and Anweiler, 1994). More productive, moist units therefore receive higher ratings as these units are more likely to produce suitable large trees. Proximity of nest trees to water and prey base is very important. Therefore, floodplain ecosystems are rated higher due to their location along major water bodies. Nesting values of all ecosystems will decrease as move away from water body. Ecosystems will likely have minimal nesting values unless they are within approximately 1.6 km of a water body or wetland. Habitats further than 1.6 km from a waterbody or wetland had reduced ratings. The impacts of human disturbance on Bald Eagles are still being argued and are of major concern in many areas (Blood and Anweiler, 1994). They were not considered in this species model due to the wilderness nature of the La Biche and Sandy Creek areas.

5 7.7.5 References Anthony, R. G., R. L. Knight, G. T. Allen, B. R. McClelland, and J. I. Hodges Habitat Use by Nesting and Roosting Bald Eagles in the Pacific Northwest. Trans North American Wildlife Natural Resource Conference 47: Anthony, R. G. and F. B. Isaacs Characteristics of Bald Eagle Nest Sites in Oregon. Journal of Wildlife Management 52(1): Blood, D. A. and G. G. Anweiler Status of the Bald Eagle in British Columbia. Wildlife Working Report No. WR-62. Prepared for the Wildlife Branch of the Ministry of Environment, Lands and Parks, Victoria, B. C. Campbell, R. W., N. K. Dawe, I. McTaggart-Cowan, J. M. Cooper, G. W. Kaiser, and M. C. E. McNall The Birds of British Columbia. Vol.II. Nonpasserines. Diurnal Birds of Prey Through Woodpeckers. Royal B.C. Museum, Victoria, B.C. Gerrard, J. M., P. N. Gerrard, W. J. Mather, and D. W. A. Whitfield Factors Influencing Nest Site Selection of Bald Eagles in Northern Saskatchewan and Manitoba. Blue Jay 33: Labine, M. Personal communication. 1997, Renewable Resource Officer III. Renewable Resources. Fort Liard, Northwest Territories. Livingstone, S. A., C. S. Todd, W. B. Krohn, and R. B. Owen Habitat Models for Nesting Bald Eagles in Maine. Journal of Wildlife Management 54(4): Peterson, A Habitat Suitability Index Models: Bald Eagle (Breeding Season). U.S. Fish Wildlife Service Biology Report 82(10.126). Resources Inventory Committee. 1997a. Standards for Wildlife Habitat Capability/Suitability Ratings in British Columbia. Review Draft, May 18, Wildlife Interpretations Subcommittee, Wildlife Branch, Ministry of Environment Lands and Parks, Victoria, B.C. Resources Inventory Committee. 1997g. Wildlife Habitat Assessment Form and Coding Rules. Final draft, May 1, Wildlife Interpretations Subcommittee, Wildlife Branch, Ministry of Environment Lands and Parks, Victoria, B.C.