The roles of environmental and geographic variables in explaining the differential wintering distribution of a migratory passerine in southern Europe

Recently Gerard Bota together with Juan Arizaga, David Mazuelas (Departamento de Ornitología de Aranzadi), and Pablo Vera (ICBiBE)  have published a new paper at the Journal of Ornithology. Below you can read the abstract:

“In birds, spatial segregation between age or sex categories during the non-breeding period is a common phenomenon. The main single-factor hypotheses that have been stated to explain this are: (1) body-size variations (that result in more or less cold tolerance) interact with local climate, which promotes age- or sex-associated distributional optima; (2) the dominant age or sex monopolizes high-quality areas; and (3) the age or sex overwintering closer to breeding quarters does so due to the benefits of earlier arrival at the breeding quarters. Southern European countries host millions of birds from northern Europe during the winter period each year. In this work, we aimed to determine the ultimate causes (geographic location and distance to obligate migratory pathways, temperature and land use as a surrogate for food availability) explaining spatial segregation of Reed Buntings (Emberiza schoeniclus) by age and sex in winter. We used data from 38 sampling points across Iberia during the winter of 2011–2012. Reed Bunting abundance did not fit any of our possible models better than the null model, so we were unable to predict bird numbers across Iberia. Moreover, males were found to be predominant at sites close to presumably obligate migratory pathways (western/eastern Pyrenees). Body mass was higher in first-year birds and males, and tended to increase with distance to obligate migratory pathways, land use (in particular with a decreasing proportion of open habitats and urban areas), increasing minimum temperature, and decreasing mean temperature. Our data suggest that the increase in the proportion of males close to obligate migratory pathways is associated with the advantage to males in wintering as close as possible to breeding quarters.”

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