TWEL Alicia Brunner Thesis

The Winter Ecology and Response to Environmental Change of a Neotropical Migratory Songbird: the Swainson’s Warbler

Alicia Rae Brunner, MS

Advisor: Christopher M. Tonra

Thesis

The ecological impacts of anthropogenic climate change are widespread, and rapid responses, such as shifting distributions, are being observed in many animal populations worldwide.  The ability of a species to respond to these climate shifts is critical, and determining the adaptive capacity of vulnerable populations is important as weather patterns become increasingly variable.  Migratory birds might provide a unique opportunity to study these responses since they experience climate change in different ways as they travel thousands of miles throughout their annual cycle.  Thus far, many studies have focused on large-scale species-level responses, but since individual abilities to respond to changing conditions drive species-level adaptations, identifying behavioral plasticity at a finer-scale is important.  If individuals can modify their space use and habitat utilization during changing environmental conditions, they might avoid consequences, such as declining food during periods of drought.  Understanding if and how individuals can respond to seasonal changes in precipitation will help us make predictions about how long-term environmental change might impact populations.

My goal was to better understand if and how overwintering migratory birds respond to seasonal changes in precipitation and resources by modifying their home ranges and habitat utilization.  In the winter of 2016 and 2017, I sought to determine how a ground foraging Neotropical migrant of conservation concern, the Swainson’s Warbler Limnothlypis swainsonii, adjusted within-season movements during dry and wet periods at Font Hill Nature Preserve in Jamaica, West Indies.  I observed individuals occupying smaller home ranges in more dense habitats and modifying their home range as precipitation changed. Habitat openness had a strong effect on arthropod dry mass and denser habitats supported more arthropods on average throughout the season, although dry period prey abundance was relatively even in both mesic and xeric habitats. Swainson’s Warblers that utilized more mesic habitats shifted their home ranges farther and into denser, more xeric habitats when rainfall increased.  Individuals also altered the size of their home ranges throughout the season, demonstrating plasticity in home range size with changing conditions.  These results provide valuable evidence of the variable space use strategies that overwintering migratory birds can exhibit in response to fluctuating resources.  My findings support the idea that some migratory birds possess the behavioral plasticity in habitat use to adjust space use strategies as seasonal environmental conditions change.  Further, I found that individuals can track spatiotemporal changes in food availability while altering the structure of, but maintaining, their home ranges.  By examining the behavioral plasticity of wintering migrants to track seasonal environmental change, we can better predict the implications of long-term environmental change for future populations.