Interactive effects of fearfulness and geographical location on the population trends of breeding birds

Díaz, Mario and Cuervo, José Javier and Flensted-Jensen, Einar and Grim, Tomas and Ibáñez-Álamo, Juan Diego and Jokimäki, Jukka and Markó, Gábor and Tryjanowski, Piotr and Møller, Anders Pape (2014) Interactive effects of fearfulness and geographical location on the population trends of breeding birds. Behavioral Ecology. ISSN 1465-7279 (print), 1465-7279 (online)

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Abstract

Animal populations are currently under pressure from multiple factors that include land use and climate change. They may adapt to such effects by reducing the distance at which they flee from humans (i.e., flight initiation distance, FID), consequently modifying their population trends. We analyzed population trends of common breeding birds in relation to FID and geographical location (latitude, longitude, and marginality of the breeding distribution) across European countries from Finland in the north to Spain in the south, while also considering other potential predictors of trends like farmland habitat, migration, body size and brain size. We found evidence of farmland, migratory and larger-sized species showing stronger population declines. In contrast, there was no significant effect of relative brain size on population trends. We did not find evidence for main effects of FID and geographical location on trends after accounting for confounding and interactive effects; instead, FID and location interacted to generate complex spatial patterns of population trends. Trends were more positive for fearful populations northwards, eastwards and (marginally) towards the centre of distribution areas, and more negative for fearless populations toward the south, west, and the margins of distribution ranges. These findings suggest that it is important to consider differences in population trends among countries, but also interaction effects among factors, because such interactions can enhance or compensate for negative effects of other factors on population trends.

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