Dataset for Sex, Body Size, and Winter Weather Explain Migration Strategies in a Partial Migrant Population of American Kestrels (Falco sparverius)
Summary & Purpose
Given increasing evidence that climate change affects the annual cycles of birds, it is important to understand the mechanisms underlying individual migration strategies and population-level patterns in partial migrants. In this study, we found that thermoregulation (body size and winter temperatures) was a key driver of American Kestrel (Falco sparverius) migration decisions. The annual proportion of migrants in the population, however, was not explained by winter weather and may be the result of differential survival. We used measured stable hydrogen isotope values (δD) of talon tissues to distinguish migrant from resident kestrels in a partially migratory population of American Kestrels in southwestern Idaho during the 2013 – 2021 breeding seasons. We then evaluated drivers of migration decisions by assessing potential correlates of migration strategies, whether individuals switched migration strategies between years, and whether the proportion of migrants in the population changed over time or was correlated with winter weather. Male kestrels were 1.6 times more likely to migrate than females, and in colder than average winters, smaller birds of both sexes were more likely to migrate than larger birds. A small proportion of birds (n = 7) showed evidence of switching their migration strategies on an annual basis. There was no temporal trend in the proportion of migrants in the population, but proportions varied between years. Interestingly, there was no association between winter minimum temperature anomalies and annual migrant proportions in the population, suggesting that differential over-winter survival, or other stochastic processes, may play an important role in population composition. As winters continue to warm, fewer kestrels may migrate and more may remain resident on breeding grounds. However, it is unclear how changes in migration strategies might affect population-level patterns and resilience to climate change.
Date of Publication or Submission
We thank the Boise State University Raptor Research Center for funding. This project was supported in part by the U.S. Department of Defense, through the Strategic Environmental Research and Development Program (SERDP) under Award No. RC-2702 and a National Science Foundation REU Site Award (DBI: 1852133). An NSF grant (EAR0842367) awarded to Boise State University funded the purchase of the stable isotope mass spectrometer and associated instrumentation.
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Ranck, Sadie C.; Garsvo, Christina M.; Schwartz, Darin M.; Reynard, Linda M.; Kohn, Matthew J.; and Heath, Julie A.. (2023). Dataset for Sex, Body Size, and Winter Weather Explain Migration Strategies in a Partial Migrant Population of American Kestrels (Falco sparverius) [Data set]. Retrieved from https://doi.org/10.18122/bio_data.10.boisestate
Available for download on Saturday, September 09, 2023