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.

Sex and age-specific differences in wing pointedness and wing length in blackcaps Sylvia atricapilla migrating through the southern Baltic coast

The blackcap Sylvia atricapilla shows a complex migratory pattern and is a suitable species for the studies of morphological migratory syndrome,including adaptations of wing shape to different migratory performance.Obligate migrants of this species that breed in northern,central,and Eastern Europe differ by migration distance and some cover shorter distance to the wintering grounds in the southern part of Europe/North Africa or the British Isles,although others migrate to sub-Saharan Africa.Based on>40years of ringing data on blackcaps captured during autumn migration in the Southern Baltic region,we studied age-and sex-related correlations in wing pointedness and wing length of obligate blackcap migrants to understand the differences in migratory behavior of this species.Even though the recoveries of blackcaps were scarce,we reported some evidence that individuals which differ in migration distance differed also in wing length.We found that wing pointedness significantly increased with an increasing wing length of migrating birds,and adults had longer and more pointed wings than juvenile birds.This indicates stronger antipredator adaptation in juvenile blackcaps than selection on flight efficiency,which is particularly important during migration.Moreover,we documented more pronounced differences in wing length between adult and juvenile males and females.Such differences in wing length may enhance a faster speed of adult male blackcaps along the spring migration route and may be adaptive when taking into account climatic effects,which favor earlier arrival from migration to the breeding grounds.