The intensity of supplementary feeding in an urban environment impacts overwintering Mallards(Anas platyrhynchos)as wintering conditions get harsher

Although urbanization poses various threats to avifauna,some bird species,including Mallards(Anas platyrhynchos),choose towns and cities as their wintering habitats,possibly due to favourable temperatures and abundant anthropogenic food.In this study,we investigated how population dynamics changed in relation to winter harshness and intensity of supplementary bird feeding in Mallard,a dabbing duck species well adapted to an urban environment.We surveyed 15 city ponds for five consecutive years,counting overwintering individuals and incidents of bird feeding conducted by the citizens of Gda′nsk.Number of Mallards observed in the studied area fluctuated both annually and within seasons,with on average 327(±SD=108.5)individuals and a malebiased sex ratio reported.We observed a gradient of feeding intensity on the surveyed ponds,with number of feeding incidents ranging from 0 to 30 in a day.The results indicated that the number of Mallards increased with the bird feeding intensity,independently of the size of the studied ponds,and both males and females were similarly attracted by food provisioning.More severe wintering conditions,expressed by the percentage of the ice cover of studied ponds resulted in more birds wintering in the urban area.This effect was more pronounced in females compared to males,possibly due to females having a lower ability to withstand severe wintering conditions,forcing them to relocate towards urban areas.Our results confirm that urbanized areas may serve as wintering grounds for birds,due to additional food resources available there and milder wintering conditions compared to surrounding rural areas.

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.