Wing morphology covaries with migration distance in a highly aerial insectivorous songbird

According to classical prediction of aerodynamic theory,birds and other powered fliers that migrate over long distances should have longer and more pointed wings than those that migrate less.However,the association between wing morphology and migratory behavior can be masked by contrasting selective pressures related to foraging behavior,habitat selection and predator avoidance,possibly at the cost of lower flight energetic efficiency.We studied the handwing morphology of Eurasian barn swallows Hirundo rustica from four populations representing a migration distance gradient.This species is an aerial insectivore,so it flies extensively while foraging,and may migrate during the day using a‘fly-and-forage’migration strategy.Prolonged foraging flights may reinforce the effects of migration distance on flight morphology.We found that two wings’aerodynamic properties—isometric handwing length and pointedness,both favoring energetically efficient flight,were more pronounced in barn swallows from populations undertaking longer seasonal migrations compared to less migratory populations.Our result contrast with two recent interspecific comparative studies that either reported no relationship or reported a negative relationship between pointedness and the degree of migratory behavior in hirundines.Our results may thus contribute to confirming the universality of the rule that longer migrations are associated with more pointed wings.

Telomere shortening is associated with corticosterone stress response in adult barn swallows

When vertebrates face stressful events,the hypothalamic–pituitary–adrenal(HPA)axis is activated,generating a rapid increase in circulating glucocorticoid(GC)stress hormones followed by a return to baseline levels.However,repeated activation of HPA axis may lead to increase in oxidative stress.One target of oxidative stress is telomeres,nucleoprotein complexes at the end of chromosomes that shorten at each cell division.The susceptibility of telomeres to oxidizing molecules has led to the hypothesis that increased GC levels boost telomere shortening,but studies on this link are scanty.We studied if,in barn swallows Hirundo rustica,changes in adult erythrocyte telomere length between 2 consecutive breeding seasons are related to corticosterone(CORT)(the main avian GC)stress response induced by a standard capture-restraint protocol.Within-individual telomere length did not significantly change between consecutive breeding seasons.Second-year individuals showed the highest increase in circulating CORT concentrations following restraint.Moreover,we found a decline in female stress response along the breeding season.In addition,telomere shortening covaried with the stress response:a delayed activation of the negative feedback loop terminating the stress response was associated with greater telomere attrition.Hence,among-individual variation in stress response may affect telomere dynamics.