Modeling Landscape-scale Habitat Relations for Landbirds During Migration: Science Support for the Gulf Coast Joint Venture
In support of the Gulf Coast Joint Venture, we are using weather radar data to identify important migratory landbird stopover habitats along the western coast of the Gulf of Mexico. Radar data is then combined with landscape-scale habitat metrics to determine the factors that influence stopover habitat use along the western coast of the Gulf of Mexico.
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- Use weather radar data to identify migratory landbird stopover habitats in the Gulf Coast Joint Venture region.
- In collaboration with the Gulf Coast Joint Venture, identify landscape-scale habitat metrics that may influence migratory landbird use of stopover habitats.
- Use structural equation modeling (SEM) to assess the relative strength and the direct and indirect nature of the causal relations among variables.
Millions of landbirds migrate through the Gulf of Mexico region each spring and autumn. Migration is energetically taxing, and these migrants depend on stopover habitats to provide the food and cover needed to complete their journey. For some species, as much as 85% of annual mortality occurs during migration (Sillett and Holmes 2002). Stopover habitats in the Gulf of Mexico region have been lost or degraded due to the effects of climate change, development, agriculture, the spread of exotic species, and other factors (Barrow et al. 2005, Cohen et al. 2017). The continued loss or degradation of stopover habitat poses a risk to migrating birds, thus knowing the location and landscape composition of the areas where peak numbers of birds consistently stop to rest and forage is critical for conservation planning. The Gulf Coast Joint Venture (GCJV) is dedicated to the protection and restoration of bird habitat along the gulf coast from Texas to Alabama. One of the goals of the GCJV landbird conservation plan is to identify important stopover habitats and the landscape-scale habitat variables that influence migrant use of these areas.
We are using weather surveillance radar data and landscape-scale habitat metrics to model bird-habitat relations within 80 km of four radar stations along the western coast of the Gulf of Mexico. Collectively, the areas around the four stations (Brownsville, Corpus Christi, and Houston, TX and Lake Charles, LA) cover many of the coastal DOI-managed lands and state conservation areas from the Rio Grande River, TX to the Atchafalaya Basin, LA. We quantified the distribution of landbirds during stopover by using reflectivity data collected during spring and fall migration 2008–2012. Data was processed according to the methods of Buler and Dawson (2014) except that reflectivity data was interpolated to the sun elevation angle that corresponds to the timing of peak evening exodus. To characterize the landscape around stopover sites, we used 2006 Coastal Change Analysis Program data to measure the percent cover and habitat patch characteristics of 11 land cover types. Landscape metrics also included the length of rivers and roads within 5 km of a stopover site, and the distance from a stopover site to the nearest developed area, river, and coastline. We are using structural equation modeling (SEM) to assess the relative strength and the direct and indirect nature of the causal relations among variables measured near the Corpus Christi, TX radar station.
- Barrow, W.C., Jr., Johnson Randall, L.A., Woodrey, M.S., Cox, J., Ruelas I, E., Riley, C.M., Hamilton, R.B., and Eberly, C., 2005, Coastal forests of the Gulf of Mexico: a description and some thoughts on their conservation, in Ralph, C.J., and Rich, T.D., eds., Bird conservation implementation and integration in the Americas—Proceedings of the Third International Partners in Flight Conference, Asilomar, Calif., March 20-22, 2002: Albany, Calif., U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station, p. 450-464.
- Buler, J.J., and Dawson, D.K., 2014, Radar analysis of fall bird migration stopover sites in the northeastern U.S.: The Condor: Ornithological Applications, v. 116, p. 357-370.
- Cohen, E.B., Barrow, W.C., Jr., Buler, J.J., Deppe, J.L., Farnsworth, A., Marra, P.P., McWilliams, S.R., Mehlman, D.W., Wilson, R.R., Woodrey, M.S., and Moore F.R., 2017, How do events around the Gulf of Mexico influence migratory landbird populations?: The Condor, v. 119, no. 2, p.327-343.
- Sillett, T.S., and Holmes, R.T., 2002, Variation in survivorship of a migratory songbird throughout its annual cycle: The Journal of Animal Ecology, v. 71, no. 2, p. 296-308.