Ornis Fennica

Temporal increase in migratoriness and increasing male bias among residents in partially migrating Swedish sparrowhawks Accipiter nisus

Andreas Otterbeck — 2024-12-18

Partial migrants have populations consisting of both migratory and resident individuals. These migrants and residents experience unequal ecological conditions during winter and the underlying factors driving their decision to stay on their breeding grounds or to migrate remain debated—both from the viewpoint of populations and individuals. Here, we studied partial migration in a small raptor, the Eurasian Sparrowhawk (Accipiter nisus), from two different but interconnected perspectives: 1) explaining the patterns and variation in the ratio of migrants to residents (migratoriness) at the population level and 2) revealing how age and sex may affect the individual decision to be migratory or resident. We used citizen observation data over four decades to explore the temporal and spatial variation in the age and sex ratio of wintering resident sparrowhawks in Sweden. We found that the migratoriness unexpectedly increased with higher annual temperatures and showed long-term trend across the study period. Also, this migrant-to-resident ratio increased with smaller winter prey abundance. The average winter sex ratio was male-biased and became increasingly so over the years. We suggest that residency benefits territory-establishing males as early presence gives a competitive advantage in obtaining high-quality territories. Moreover, the distribution of overwintering individuals (regardless of sex) moved gradually northwards as the winter progressed, suggesting that smaller-scale migration occurs among the resident fraction of the population. These results provide suggestions for the underlying drivers and regulation of partial migration.

The selective consumption of European ivy (Hedera helix) berries by the Common Blackbird (Turdus merula)

Volodymyr Kucherenko — 2024-12-18

Seed dispersal of plants affects the spatial structure and population dynamics, contributing to ecosystem functioning. Birds are among the most important seed dispersers. Preferences of birds in fruit and berry consumption are potentially significant selective pressures on the evolution of fruit traits that affect plant fitness. European ivy (Hedera helix) is a widespread deciduous species in Europe and the Common Blackbird (Turdus merula) is important seed disperser. This study investigates blackbird feeding preferences for specific sizes of ivy seeds. Field data was collected in a small settlement east of Simferopol city in Crimea and included a collection of reference seeds gathered from plants and seeds found in bird excretions. The length of the major axis, minor axis, and aspect ratio were measured, and statistical analysis was performed. The length of the major and minor axes of seeds consumed by blackbirds was higher compared with the reference collection, the aspect ratio was the opposite. Evidence of size differences could suggest weak effect of selective consumption of blackbirds on seed shape. This research extends our knowledge of the ecological relationship between frugivorous birds and plants and the role of birds in directional selection in a particular locality.

A helpful and long-overdue resource for work with mountain birds

Theodore Squires — 2024-12-18

The newly released textbook, Ecology and Conservation of Mountain Birds (edited by Chamberlain, Lehikoinen & Martin), provides a comprehensive review of the latest knowledge in alpine ornithology. It summarizes the combined knowledge of over 50 subject experts and serves as an excellent reference guide for professionals and students. Here, the layout and contents of the book are reviewed and an unbiased general assesment of the contents are provided. As the global environment continues to see unprecedented changes, this work should serve as a groundbreaking benchmark describing the state of our mountain birds.