FROM COLONISATION TO COEXISTENCE: AN INTRA-GUILD MULTI-SCALE ANALYSIS AMONG NEW-ESTABLISHED SYMPATRIC FALCO SPECIES

Anthropogenic global changes are currently reshaping animal communities, with some species expanding their ranges and colonising new areas (i.e. “newcomers”), leading to new ecological interactions among pre-existing species or with other newcomers. Both lesser kestrel (Falco naumanni) and red-footed falcon (Falco vespertinus) have been recently expanding their breeding range in Northern Italy, interacting with each other, as well as with an increasing population of common kestrel (Falco tinnunculus). Since the Po Plain is the only known area in Europe where these species breed sympatrically, this system provided an excellent opportunity to investigate intra-guild niche overlap and partitioning during an initial stage of sympatry. At a broad scale, our analysis delved into spatial niche overlap, revealing a strict relation among the lesser kestrel and red-footed falcon on the eco-climatic variables affecting their current distribution. This affinity turned into a statistically significant spatial correlation in their potential distributions. At a finer scale, we found that these two species exhibited overlapping foraging habitat choices. This convergence also extended to their diets, reinforcing the possibility of exploitative competition. This hypothesis gained ground through observations of systematic kleptoparasitism by red-footed falcons on lesser kestrels, a specific foraging strategy, first described in the present work. In contrast, the common kestrel displayed as a habitat generalist on the broad scale, being ubiquitarian throughout the study area. At a finer scale, its foraging habitat resulted to be slightly, yet significantly, different from that of lesser kestrel and red-footed falcon. Coherently, its wide trophic niche was including those of the two other falcons. Noteworthily, no evidence of kleptoparasitic behaviour involving the common kestrel was ever collected in the study area, neither as an aggressor nor as a victim species. This comprehensive investigation of spatial niche overlap, foraging habitat, trophic dynamics and aggressive behaviour shade light on the complex interspecific relationships in a guild of “newcomer” species. Our results thus provide an original in-depth assessment of how global changes are affecting predator communities via potential indirect competition and behavioural interference at the intra-guild level.