Species traits and latitude mediate bird responses to forest edges globally

Other supplementary material in Vallejos et al. 2024 

Context :               Although local studies comparing species abundance between forest edges and interiors are common, general patterns in the response of different species to edges are still to be determined. There is little consensus on the impacts of forest edge effects on the abundance of individual bird species, probably because the species traits affecting edge responses have rarely been synthesized.

Objective  :           We aimed to identify how different species’ traits, as well as extrinsic (environmental) factors, mediate the responses of birds to forest edges globally.

Methods  :              We collected global information from bibliographic databases from 59 studies with 63 different datasets that compared bird abundance between forest edges and interiors. For each species, we compiled six traits (diet, habitat preference, territoriality, body mass, hand-wing index, and foraging stratum). Using Linear Mixed-effects Models, we evaluated how species traits, latitude, edge contrast, and sampling method affected bird responses to edges.

Results      :           Based on 2,981 responses of 1,414 bird species, we found that plant/seedeaters birds responded positively to edges. The strength of habitat preference on edge responses was also mediated by latitude. Open-area species from tropics exhibited a positive response, diminishing as latitude increases. Conversely, forest species tend to exhibit a somewhat more negative response in tropical zones. Edge effects were more negative for soft (low-contrast) edges.   

Conclusions  :       Species traits, in particular diet and habitat preferences interacting with latitude, mediate the impacts of edge effects on different bird species. These species traits and latitudinal gradients must be explicitly considered in models attempting to explain variability in edge responses among species, as well as in conservation actions in fragmented landscapes.