Meeting Abstract
Each spring, neo-tropical migratory birds traverse the Gulf of Mexico en route to their breeding grounds, often stopping to refuel along the northern Gulf coast. Baseline levels of the metabolic hormone corticosterone (CORT) have been hypothesized to be elevated during migratory flight, reduced during refueling at stopover sites, and increased again prior to departure. During spring migration in 2017, we examined Gray Catbirds (Dumetella carolinensis) on St. George Island, a Florida panhandle barrier island and first landfall site for many trans-Gulf migrants. We sought to test the predicted relationships among CORT, refueling rate, and body condition during stopover. We measured baseline CORT, body mass, plasma triglycerides, and precise body composition using a Quantitative Magnetic Resonance analyzer (QMR). We found that birds with low body-, fat-, and lean mass had higher baseline CORT levels. These data are consistent with the hypothesis that baseline CORT declines at stopovers as body condition improves. However, refueling rate (as indicated by plasma triglycerides) was not predicted by CORT. Our data were not able to detect an increase in baseline CORT prior to departure. This may be because Gray Catbirds don’t stay long on the island, instead relocating to the mainland to continue their stopover phase. Feather deuterium values will be analyzed to clarify the migration destinations of these individuals and provide context to our findings.
