Meeting Abstract
During spring migration, long-distance migratory birds fly faster, have higher refueling rates at stopovers, and are more likely to encounter inclement weather compared to fall migration. Together, these observations suggest that migration is likely more challenging in the spring than the fall. As the hypothalamic-pituitary-adrenal (HPA) axis helps vertebrates appropriately respond to environmental challenges and stressors, we examined whether HPA-axis activity and regulation differed between fall and spring migration in a long-distance migrant. We measured baseline corticosterone (CORT), stress-induced CORT, and negative feedback efficacy in migratory, slate-colored Dark-eyed Juncos (Junco hyemalis hyemalis) during their fall and spring stopovers in Fargo, North Dakota. Spring migrants had higher body weight, fat stores, and hematocrit compared to fall migrants. While baseline and stress-induced CORT did not significantly differ between fall and spring stopovers, migrants had weaker negative feedback in the spring. These findings fit well with the hypothesis that HPA-axis activity helps mediate initiation of breeding (the CORT-Flexibility Hypothesis), and suggest that stress sensitivity may help individuals appropriately respond to prevailing environmental conditions and alter timing of reproduction after arrival to the breeding grounds.
