Baseline corticosterone in wintering marine birds: methodological considerations and ecological patterns

Area of Science:

• * Wildlife physiology
• * Avian ecology
• * Stress hormone research

Background:

• * Plasma corticosterone (CORT) links seabird foraging to breeding conditions.
• * Baseline CORT during non-breeding periods remains poorly understood.
• * Validating methods for baseline CORT measurement in lethally sampled birds is crucial.

Purpose of the Study:

• * To validate methods for obtaining baseline CORT from lethally sampled white-winged scoters.
• * To assess if baseline CORT levels correlate with winter habitat conditions.
• * To understand physiological strategies of wintering seabirds.

Main Methods:

• * Lethal sampling of free-living white-winged scoters (Melanitta fusca) in four wintering sites.
• * Measurement of plasma corticosterone (CORT) and time since flush (TSF).
• * Analysis of habitat variables: wind/wave exposure, predation risk, diving depth, and diet.

Main Results:

• * Baseline CORT can be accurately measured from lethally sampled birds if TSF is recorded.
• * Increasing CORT values beyond 3 minutes post-flush indicate acute stress responses.
• * Baseline CORT levels did not significantly differ across study sites or winter months.

Conclusions:

• * White-winged scoters maintain stable baseline CORT despite varying winter habitat conditions.
• * Birds likely select wintering sites that allow them to manage environmental costs and maintain homeostasis.
• * Findings provide insights into seabird physiological resilience during winter.