Isotopic niches of tropical birds reduced by anthropogenic impacts: a 100-year perspective

Abstract

The intensification of land-use changes in tropical forests during the 20th century, mainly caused by deforestation for agricultural uses, had an overwhelming influence on bird assemblages. However, how these historical anthropogenic changes have impacted the habitat use and diet of tropical birds is poorly known. Stable isotope analysis (δ13C and δ15N) can be useful in this regard since it provides information not only on the habitat and food resource use but also insights on the dietary niche of species. Here, we aimed to evaluate whether centenary anthropogenic impacts, mainly caused by changes in landscape composition, have affected the resource and habitat use and isotopic niche width of Neotropical birds in a region that comprises two biodiversity hotspots – the Atlantic Forest and Cerrado in southeastern Brazil. We found that the niche width of all bird guilds (frugivore, granivore, insectivore, nectarivore and omnivore) was largely reduced (28–70%) from the 20th century until recently. This niche width reduction was likely associated with historical anthropogenic impacts (e.g. fragmentation, forest loss and change in agricultural practices), which are responsible for the decrease in the availability of habitat and food resources. Moreover, the mean values of δ15N decreased over the years in all bird guilds, which might be attributed to the expansion of agricultural areas and the increase in the use of synthetic nitrogen-based fertilizers. All the analyzed species, even though some of them are diet and habitat generalists, were strongly influenced by centenary anthropogenic actions. Our results show the consequences of human-induced changes in land use on the diet and habitat use of tropical birds that persist in fragmented landscapes, which might compromise their long-term survival and provide useful information to the conservation strategies of bird assemblages in modern landscapes.