Holding steady: Little change in intensity or timing of bird migration over the Gulf of Mexico

Authors: Kyle G. Horton 1 | Benjamin M. Van Doren 2 | Frank A. La Sorte 1 | Emily B. Cohen 3 | Hannah L. Clipp 4 | Jeffrey J. Buler 4 | Daniel Fink 1 | Jeffrey F. Kelly 5,6 | Andrew Farnsworth 1

Year: 2019

Publication: Global Change Biology

Publication Link: https://doi.org/10.1111/gcb.14540

Access: Open

Affliations: 1 Cornell Lab of Ornithology, Cornell University, Ithaca, New York
2 Edward Grey Institute, Department of Zoology, University of Oxford, Oxford, UK
3 Migratory Bird Center, Smithsonian Conservation Biology Institute, National Zoological Park, Washington, District of Columbia
4 Department of Entomology and Wildlife Ecology, University of Delaware, Newark, Delaware
5 Department of Biology, University of Oklahoma, Norman, Oklahoma
6 Corix Plains Institute, University of Oklahoma, Norman, Oklahoma

Corresponding Author: Kyle G. Horton, Cornell Lab of Ornithology,
Cornell University, Ithaca, NY.
Email: kgh48@cornell.edu

Funding: NSF Division of Biological Infrastructure, Grant/Award Number: DBI-1356308, DBI-1661259, DBI-1661329; Leon Levy Foundation; The Wolf Creek Charitable Foundation; NSF Division of Emerging Frontiers, Grant/Award Number: EF-1340921; NSF Division of EnvironmentalBiology, Grant/Award Number: DEB-110008; NSF Division of Information and Intelligent Systems, Grant/Award Number: IIS-1125098; National Fish and Wildlife Foundation; Edward Rose Postdoctoral Fellowship

Keywords: climate change, eBird, Gulf of Mexico, migratory birds, phenology, weather surveillance radar

Abstract: Quantifying the timing and intensity of migratory movements is imperative for understanding impacts of changing landscapes and climates on migratory bird populations. Billions of birds migrate in the Western Hemisphere, but accurately estimating the population size of one migratory species, let alone hundreds, presents numerous obstacles. Here, we quantify the timing, intensity, and distribution of bird migration through one of the largest migration corridors in the Western Hemisphere, the Gulf of Mexico (the Gulf). We further assess whether there have been changes in migration timing or intensity through the Gulf. To achieve this, we integrate citizen science (eBird) observations with 21 years of weather surveillance radar data (1995–2015). We predicted no change in migration timing and a decline in migration intensity across the time series. We estimate that an average of 2.1 billion birds pass through this region each spring en route to Nearctic breeding grounds. Annually, half of these individuals pass through the region in just 18 days, between April 19 and May 7. The western region of the Gulf showed a mean rate of passage 5.4 times higher than the central and eastern regions. We did not detect an overall change in the annual numbers of migrants (2007–2015) or the annual timing of peak migration (1995–2015). However, we found that the earliest seasonal movements through the region occurred significantly earlier over time (1.6 days decade−1). Additionally, body mass and migration distance explained the magnitude of phenological changes, with the most rapid advances occurring with an assemblage of larger‐bodied shorter‐distance migrants. Our results provide baseline information that can be used to advance our understanding of the developing implications of climate change, urbanization, and energy development for migratory bird populations in North America.

Intrusive Methodologies: None

Citizen Science: eBird

Conservation: “The resulting information is also important to inform modeling efforts designed to predict the long‐term implications of different climate change scenarios and inform conservation efforts within the Gulf of Mexico region.”

 

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