Raptors, doves and fragmented landscapes: Overabundance of native birds elicit numerical and functional responses of avian top predators

Abstract

The replacement of natural habitats by fields destined for agricultural-livestock production causes changes in species composition. Some species benefitting from these changes can become more abundant. Increased populations can alter trophic webs. In the center of Argentina, populations of the native eared dove (Zenaida auriculata) have increased significantly in several provinces to such an extent that the species has been declared a pest. In 2014, 20 transects were sampled monthly to determine spatial and temporal abundance fluctuations of two raptor species, the crested caracara (Caracara plancus) and the black-chested buzzard eagle (Geranoaetus melanoleucus) to increases in the population of eared doves. The diet of these birds of prey was determined over 10 years, between 2003-2007 and 2010-2015. The monthly average (± SD) of crested caracaras and black-chested buzzard eagles was 97.75 (± 33.6) individuals and 3.91 (± 3.0) individuals, respectively. The monthly average of eared doves during surveys was 63,460 (± 113,497) individuals. Although both raptor species strongly rely on eared doves as their main prey, only black-chested buzzard eagle's trophic niche breadth was determined by the presence of this prey by having a potential functional response. The crested caracara, by contrast, could show a numerical response to increase of eared dove abundance that was not evident with the black-chested buzzard eagle. Anthropogenic disturbances and habitat fragmentation are the main drivers of eared dove overabundance, whose populations can cause changes in the composition and structure of these two raptor communities and consequently disturb ecosystem processes.