Corticosterone secretion patterns prior to spring and autumn migration differ in free-living barn swallows (Hirundo rustica L.)

Abstract

Recent studies of long-distance migratory birds show that behavioural and physiological changes associated with predictable or unpredictable challenges during the annual cycle are distinctively regulated by hormones. Corticosterone is the primary energy regulating hormone in birds. Corticosterone levels are elevated during stresses but they are also modulated seasonally according to environmental conditions and life-history demands. We measured the baseline and stress-induced levels of corticosterone in the barn swallow (Hirundo rustica L.) just before spring and autumn migrations in South Africa and Finland, respectively. Barn swallows completing their pre-breeding moult had low body condition (residual body mass) and high baseline corticosterone levels in the wintering grounds. In contrast, baseline corticosterone levels in Finland were low and not related to residual mass. These data contradict the first prediction of the migration modulation hypothesis (MMH) by showing no association with baseline corticosterone levels and pre-migratory fuelling. Yet, the adrenocortical response to the capture and handling stress was notably blunted in South Africa compared to a strong response in Finland. Further, individuals that had started fuelling in Finland showed a reduced response to the handling stress. Taken together, elevated baseline corticosterone levels and high residual mass may blunt the adrenocortical response in long-distance migrants and aerial feeders such as the barn swallow. This observation lends support to the second prediction of the MMH.

Why Do Animals Do What They Do, When They Do It? Characterizing the Role of the Hypothalamus-Pituitary-Adrenal Axis in Seasonal Life-History Transitions

“…Female Lapland longspurs experience peak stress-induced corticosterone at an earlier sampling time during the breeding season than when sampled during migration . Differences in HPA axis activity between spring and fall migration occur in other bird species as well (Eikenaar et al, 2015;Raja-aho et al, 2013;Romero et al, 1997). Together, these studies suggest that migration-related changes in the stress response may be a conserved function of the HPA axis across taxa, but further research will be required to test this hypothesis.…”