How area sensitivity in birds is studied.

Studies of avian area sensitivity have been prolific over the last 3 decades, yet general conclusions about the phenomenon are lacking. We undertook a systematic literature review to determine how widespread area sensitivity is; whether published information is biased toward certain geographic regions, habitat types, or taxonomic groups; whether the nature of area effects varies with respect to these criteria; and whether tests of area effects for individual species produce consistent results. Analysis of over 2700 area sensitivity tests, from more than 870 species, indicated the phenomenon is widespread across regions, habitats, and taxonomic groups, but that significant biases in research focus exist. North American forest habitats and Passeriformes (especially Fringillidae, Regulidae, and Paridae) are disproportionately represented in the literature. Detection of area effects was more common in tests of occurrence (47%) than in those for abundance (25%) and varied significantly among regions, habitats, and taxonomic groups. Inconsistent results for species studied multiple times and between tests of occurrence and abundance were common. These results suggest a need for future research to focus more on why area sensitivity patterns differ among studies and less on simple pattern description.