Foraging niche partitioning within a recently established guild of falcons

Ecological theory predicts that coexisting species should exhibit realized niche differentiation to minimize competition. However, little is known about patterns of niche differentiation when ‘newcomer’ species spontaneously colonize a new region, leading to novel sympatric conditions. Over the past 15 years, three closely related and ecologically similar falcon species (Common Kestrel Falco tinnunculus, Lesser Kestrel Falco naumanni and Red-footed Falcon Falco vespertinus) have expanded their ranges as the result of land-use and climate changes in the intensively cultivated agroecosystems of the Po Plain (Northern Italy). This is a unique condition in the European range of these species and provides an excellent opportunity to investigate patterns of foraging and trophic niche partitioning during the initial phases of sympatry. We assessed species-specific patterns of foraging habitat selection and interspecific differences in diet composition. Our findings showed that falcons selected largely overlapping foraging habitats, yet exhibited significant differentiation among species regarding vegetation height, structure and crop types. Overall, diet composition was similar, though some degree of trophic niche differentiation was detected. In line with the niche partitioning hypothesis, the three species slightly partitioned their foraging and trophic niches, probably playing a key role in making syntopic coexistence possible. Our study provides insights into the mechanisms of niche partitioning when ‘newcomers’ appear in a guild, a process that is likely to become increasingly relevant because of the rapid and often uneven distributional shifts caused by global change.