Interactive effects of fearfulness and geographical location on bird population trends

Animal populations are currently under pressure from multiple factors that include human land use and climate change. They may\udcompensate for such effects by reducing, either by habituation or by natural selection, the distance at which they flee from humans\ud(i.e., flight initiation distance), and this adaptation may improve their population trends. We analyzed population trends of common\udbreeding birds in relation to flight initiation distance and geographical location (latitude, longitude, and marginality of the breeding distribution)\udacross European countries from Finland in the north to Spain in the south while also considering other potential predictors of\udtrends like farmland habitat, migration, body size, and brain size. We found evidence of farmland, migratory, and smaller-sized species\udshowing stronger population declines. In contrast, there was no significant effect of relative brain size on population trends. We did\udnot find evidence for main effects of flight initiation distance and geographical location on trends after accounting for confounding and\udinteractive effects; instead, flight initiation distance and location interacted to generate complex spatial patterns of population trends.\udTrends were more positive for fearful populations northward, westward, and (marginally) toward the center of distribution areas and\udmore negative for fearless populations toward the south, east, and the margins of distribution ranges. These findings suggest that it\udis important to consider differences in population trends among countries, but also interaction effects among factors, because such\udinteractions can enhance or compensate for negative effects of other factors on population trends.This article is a contribution by M.D. to the project RiskDisp\ud(CGL2009-08430) and to the thematic networks GlobiMed (www.globimed.\udnet) and REMEDINAL III S2013/MAE-2719. JJ received support from the EU Regional\udDevelopment Fund via the Project “Rovaniemen kaupunkilintuatlas (A31026).Peer reviewe