Body mass and triglycerides predict departure of free-living nomadic pine siskins

1. Facultative migrations are observed across vertebrate taxa, include irruptive and nomadic movements, and occur in response to ephemeral and unpredictably variable resources. While the physiology underlying seasonal, obligate migrations is thoroughly studied, much less is known about the physiological mechanisms of facultative movements. We test two hypotheses in a free-living, nomadic bird, the pine siskin (Spinus pinus).
2. The Prepare Hypothesis predicts that, like obligate migrants, siskins increase fuel stores to prepare for migratory movements and elevations of baseline corticosterone (CORT) support departure. The Escape Hypothesis predicts that siskins do not prepare for departure, body condition declines as food availability declines, and stress-related levels of CORT induce escape from resource-poor areas.
3. Under the controlled lab conditions of previous studies, food restriction induces declines in body condition and increases in CORT and locomotor activity, supporting the..., See manuscript for details: DeSimone, JG, Domschot, BS, Fylling, MA, Blake, WM, and Breuner, CW. 2022. Body mass and triglycerides predict departure of free-living nomadic pine siskins. Functional Ecology. Accepted., See READme file for details