HABITAT USE BY BIRDS OF MATURE AND REVEGETATED TRACTS ALONG THE LOWER RIO

Transcription

1 HABITAT USE BY BIRDS OF MATURE AND REVEGETATED TRACTS ALONG THE LOWER RIO Timothy Brush and Teresa P. Feria Current

2 Avian Diversity in the Lower Rio Grande Over 500 species of birds-->80% of species in Texas, ~50% of species in North America north of Mexico A subset of species are mainly tropical in distribution. Some have declined greatly due to habitat loss and deterioration.

3 Project Need 38 ha 195 ha 22 ha Habitat loss and fragmentation of an estimated 95% of the Rio Grande riparian corridor has left isolated fragments surrounded by agricultural land (Jahrsdoerfer and Leslie 1998). Many woodland bird species have declined. Jahrsdoerfer, S. E., Leslie, D. M., Jr (1988) 'Tamaulipan Brushland of the Lower Rio Grande Valley of South Texas: Description, Human Impacts, and Management Options', Biological Report (U.S. Fish and Wildlife Service - Oklahoma Cooperative Fish and Wildlife Research Unit), 88(36).

4 Efforts to combat habitat loss Image taken from USFWS The US Fish and Wildlife Service and other agencies have undertaken efforts to restore habitats along the Rio Grande, with the goal of creating additional habitat, to allow for dispersal of various organisms and overall increases In

5 Goals 1) The main goal of this monitoring project was to compare bird use of existing mature riparian habitats with those that have been revegetated 2) Given rapid urbanization, we also wanted to do a preliminary exploration of bird use in urban woodlots and mature urban habitats Huang, Y. and Fipps, G. (2006) Landsat satellite multispectral image classification of land cover change for GISbased urbanization analysis in irrigation districts: evaluation in the Lower Rio Grande Valley

6 A word about riparian habitat in the Lower Rio Grande Valley We use the broad sense, which includes tall riparian forest and thorn-forest, since both are influenced by the river. Habitats are often mixed together. Due to long-term drought and lack of seasonal flooding, most of the riparian habitat is now thorn-forest (usually >3 m tall) or thorn-scrub (1-2 m tall).

7 Study Area We established study points in the boxed area, which contains most of the remaining thorn-forest and associated habitats in the Lower Rio Grande Valley.

8 Census locations & site selection 106 census plots were selected, 92 in mature and reveg, 14 in urban mature and residential (smaller # in urban areas is a reflection of preliminary exploration) Points in revegetated habitats were placed in proximity to mature areas, to control for environmental factors as much as possible. All revegetated areas we included are within 10

9 Examples of mature and revegetated habitats Mature thorn-forest was dense, with a closed canopy and well-developed leaf litter. Revegetated habitats varied, but some approached mature habitat in structure.

10 We obtained foliage profile data, using the pole method (Mills et al. 1991). Lighter blue = mature habitat, darker blue = revegetated habitat. Overall, mature habitat was Mills, G.S., J.B. Dunning, and J.M. Bates On the relationship between bird density and vegetation volume. Wilson Bull. 61:

11 We chose urban habitats that were as welldeveloped as possible, with dense foliage and Urban woodlots Mature urban small wooded parks; often quite similar to mature thorn-forest but with open areas older, diverse neighborhoods-- sometimes with trees suitable for cavities

12 Point Count Methodology We followed standard point count methodology (Ralph et al. 1993) At each point we conducted a total of 4 ten-minute bird counts during May and June of 2013 and 2014, between We recorded birds in distance bands of 0-25 m, m, m, and >100 m using sight and sound Visualization of point count methodology. Taken from USGS. Only birds detected within 100 m were used for frequency analysis, to allow for determination of habitat associations Birds seen flying over or through the habitat were recorded at >100 m distance Ralph, C.J., G.R. Geupel, P. Pyle, T.E. Martin, and D.F. DeSante Handbook of field methods for monitoring landbirds. U.S. Forest Service Gen. Tech. Rep. PSW- GTR-144.

13 Results Frequency = # of times x species detected in x habitat/total # of surveys done in x habitat For example, Olive Sparrow occurred on 88.3% of mature surveys, but only on 46.4% of mature urban surveys We found several different patterns of habitat use first, some examples Olive Sparrow Ladder-backed Woodpecker Altamira Oriole Yellow-billed Cuckoo Mourning Dove Northern Mockingbird Golden-fronted Woodpecker Brown-crested Flycatcher Red-crowned Parrot White-winged Dove White-tipped Dove Long-billed Thrasher Plain Chachalaca Great Kiskadee Clay-colored Thrush Northern Beardless Tyrannulet Black-crested Titmouse Gray Hawk

14 Some species, formerly characteristic of tall riparian forest and thorn-forest, were not detected on points. Red-billed Pigeon a GCPLCC focal species--formerly common in riparian forest across the LRGV now rare breeder upstream from study area--one flyover in May 2013 at Santa Ana NWR. Rose-throated Becard was uncommon breeding resident in 1930s-1960s; now very rare, irregular resident, with no successful breeding records since 1970s. Probably affected by loss of tall riparian forest and habitat loss in adjacent Tamaulipas. Tropical Parula was habitat specialist in tall riparian forest with abundant Spanish moss now rare migrant/ winter visitor in the LRGV. Audubon s Oriole--was widespread until 1960s, but greatly affected by habitat fragmentation and cowbird

15 Some species made little distinction between mature and revegetated habitats 90.0% OLIVE SPARROW ALTAMIRA ORIOLE LADDER-BACKED WOODPECKER 67.5% Frequency 45.0% 22.5% 0% Mature Reveg Urban Woodlots Mature Urban Habitat

16 Some species preferred mature habitats over revegetated 100.0% WHITE-WINGED DOVE WHITE-TIPPED DOVE LONG-BILLED THRASHER 75.0% Frequency 50.0% 25.0% 0% Mature Reveg Urban Woodlots Mature Urban Habitat

17 Others made greater use of revegetated habitats 100.0% NORTHERN MOCKINGBIRD YELLOW-BILLED CUCKOO MOURNING DOVE 75.0% Frequency 50.0% 25.0% 0% Mature Reveg Urban Woodlots Mature Urban Habitat

18 Still others preferred urban areas, perhaps because of richer food resources % PLAIN CHACHALACA CLAY-COLORED THRUSH GREAT KISKADEE 75.0% Frequency 50.0% 25.0% 0% Mature Reveg Urban Woodlots Urban Mature Habitat

19 Uncommon tropical species were more widespread than expected. 9.0% NORTHERN BEARDLESS-TYRANNULET GRAY HAWK ALTAMIRA ORIOLE 6.8% Frequency 4.5% 2.3% 0% Mature Reveg Urban Woodlot Mature Urban Habitat

20 At the community level, mature and revegetated habitats were quite similar, as these top 10% lists show Mature Revegetated OLIVE SPARROW 88.3% OLIVE SPARROW 89.0% NORTHERN CARDINAL 80.6% NORTHERN MOCKINGBIRD 80.2% GOLDEN-FRONTED WOODP. 77.0% MOURNING DOVE 75.0% WHITE-WINGED DOVE 73.0% YELLOW-BILLED CUCKOO 69.8% WHITE-TIPPED DOVE 63.8% NORTHERN CARDINAL 66.3% COUCH'S KINGBIRD 63.3% GOLDEN-FRONTED WOODP. 54.7% YELLOW-BILLED CUCKOO 62.2% COUCH'S KINGBIRD 52.9% MOURNING DOVE 60.2% BROWN-CRESTED FLYCATCHER 48.8% NORTHERN MOCKINGBIRD 58.2% LADDER-BACKED WOODP. 46.5% BROWN-CRESTED FLYCATCHER 56.1% WHITE-WINGED DOVE 44.8%

21 Principal components analysis revealed groups of birds that responded similarly to particular habitat features 1) Mature thorn-forest: high litter quality and canopy cover, Texas ebony foliage and foliage density at 1-4 m (mostly in mature habitat)--- White-winged Dove, White-tipped Dove, Plain Chachalaca, Long-billed Thrasher, and Altamira Oriole 2) Semi-open woodlands (mature and reveg): high tree diversity, some fruiting species (mature and reveg) Golden-fronted Woodpecker (taller) and Yellowbilled Cuckoo (shorter) 3) Tall, mesic riparian forest: foliage at 4-6 m, abundant cedar elms and other tall trees, often adjacent to wetlands or scrub (mostly mature) Carolina Wren*, Common Yellowthroat*, Lesser Goldfinch to Dense, low thorn-forest: mixed wooded and grass (mature and reveg) Verdin, Common Ground- Dove

22 Partial least squares regression revealed a variety of responses--some similarity to PCA Mature habitat: Plain Chachalaca, White-winged Dove. Revegetated habitat: Mourning Dove, Brown-crested Flycatcher, Black-crested Titmouse, Great-tailed Grackle, Brown-headed Cowbird High canopy cover: Common Ground-Dove, Yellow-billed Cuckoo, White-eyed Vireo, Carolina Wren, Long-billed Thrasher*, Lesser Goldfinch Low canopy cover: Brown-crested Flycatcher, Verdin *only species avoiding habitat edges

23 Mature urban habitats were the most distinct

24 A complicating factor was the extended 2010 flood, after 6 years of drought, that killed mature trees in low spots. It probably did not change results but may have reset vegetation. A future study

25 Conclusions 1) Bird use of mature and revegetated habitats Bird species that prefer the mature thorn forest habitat (high canopy cover, good litter quality, little grass invasion) did have lower frequencies in revegetated habitats. Preservation of these remnant forests is necessary in the short run. Revegetated habitats supported many of the common breeders of the LRGV. These tracts (often years old) hosted a similar bird community to mature tracts: thus, revegetation can be considered successful for many species. In the future, these reveg tracts should more closely resemble mature habitats. Habitat needs of specialized species need to be more fully explored. 2) Preliminary data on bird use of urban habitats in the LRGV The relatively high use of urban woodlots and mature urban (residential) habitats by many species is encouraging. Patches of mature habitat within urban matrix are suitable for many mature forest species. Well vegetated residential habitats can also support unique species like Red-crowned Parrot and Green Parakeet, and warrant further investigation as another means of habitat restoration.

26 Currently we are expanding our study of urban habitats to include newer neighborhoods. Many recent

27 Continued studies in riparian habitats will focus on analyzing habitat needs of species of conservation concern and ways to increase habitat suitability at low cost.

28 Many thanks to the Gulf Coast Prairie Landscape Conservation Cooperative and the Rio Grande Joint Venture for their financial support and interest! Personnel of the US Fish and Wildlife Service, Texas Parks and Wildlife Department, and private landowners allowed access to study areas Field data collection was collected by John Brush and Edwin Quintero Data entry and analysis were performed by John Brush and Mayra Oyervides Wildlife Management Institute and personnel of the University of Texas-Pan American handled financial aspects. Special thanks to Mary Gustafson for