The Effects Of Global Climate Change On Long-Distance Migratory Birds

Abstract

Global climate change is altering conditions across the globe. These changes are happening asynchronously among regions, creating asymmetrical changes for species whose life cycles span hemispheres. This dissertation is an attempt to use the effects of global climate change on the annual cycle of the long-distance migratory bird, the Hudsonian Godwit, Limosa haemastica, as a lens for understanding the broader effects of global climate change on all migratory birds. Using geolocation tracking devices and intensive breeding season studies, I show how different populations within the same species are differentially affected by climate change and how this arises because of differences in the climate change regimes experienced by the two populations, but also underlying differences in the amount of flexibility that exists in their respective annual cycles. In response to different climate change regimes, the Hudsonian Godwit populations breeding at Beluga River, Alaska and Churchill, Manitoba are altering the timing of their arrival on their breeding grounds in different ways. Beluga River godwits, which are experiencing only warming climates throughout their annual cycle, have accelerated their arrival on their breeding grounds by nearly 9 days over the past four decades. Churchill godwits, which are experiencing both warming and cooling climates, have instead retarded their arrival by more than 10 days during that same time period. These different trends allow Beluga River godwits to remain properly timed with the period of peak insect abundance and maintain a robust breeding success rate, while Churchill godwits are instead suffering a phenological mismatch and frequent reproductive failure. Beluga River godwits are able to respond to such climatic changes because their annual cycle includes buffer events and flexibility in timing. As a result of this buffer, Beluga River godwits are able to absorb delays caused by extreme weather events that disrupt their northward migration, without suffering reductions in breeding success. Using these findings and an organismenvironment approach to the whole annual cycle, I suggest that those species and populations with larger amounts of flexibility in their annual cycles can withstand significant climatic change, but that those lacking flexibility are in danger of rapidly succumbing to climatic change.