| Summary: | Climate change can cause mismatches between the breeding phenology and peak abundance of food resources of migratory species. Moreover, asynchronously changing climate regimes across their ranges may constrain the ability of migratory species to adapt to all the regimes they encounter. To understand the potential effect of asynchronous changes, I examined the influences of both large- and local-scale weather and climate on the timing of arrival of two disjunct breeding populations of Hudsonian Godwits (Limosa haemastica). I used arrival data from two study sites—Beluga River, Alaska, and Churchill, Manitoba—combined with 37 years of weather and climate data from both winter and stopover sites and the breeding grounds. The Alaskan population now arrives ∼9 days earlier than it did in the early 1970s, and the Churchill population arrives >10 days later. A model-selection process using linear regression models suggested that these divergent trends result from different suites of environmental factors affecting the timing of migration for the two populations. The cues used by the Alaskan population have remained reliable indicators of the timing of the onset of spring on their breeding grounds, but this is not the case for the Churchill population. Conflicting warming regimes in midcontinental North America cause the Churchill population to arrive later to their breeding grounds and limit their ability to properly time their breeding efforts. These results suggest that ecological and phenological limitations, not just evolutionary constraints, are critical to determining how populations respond to climate change.
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