Competitive interactions of two sympatric raptors affecting their spatial distribution in an island environment

Abstract

Competition within and between species affects community structure and is well documented in raptors. We investigated the spatial distribution of two sympatric raptors in Cyprus, the Bonelli’s Eagle (BE) and the Long-legged Buzzard (LLB). Both species are facultative tree/cliff nesters, with overlapping nesting and foraging areas. In 2021, the BE population consisted of 40 pairs with a density of 1,3 pairs/100 km², and the LLB population of 113 pairs with 2,9 pairs/100 km². About 80% of BE nesting sites and 43% of LLB nesting sites were situated within the Natura 2000 (N2K) protected areas network while 97% of BE nesting sites and 91% of LLB’s were situated within 2.5 km from N2K areas. The spatial distribution was compared between and within species based on Nearest Neighbour Distance (NND) analysis. Average intraspecific NND for BE was 6.158 ± 2.207 m (SD), almost double compared to LLB which was 3.151 ± 1.730 m (SD). The distribution of BE nesting territories showed a regular spacing, indicating a stronger effect of intraspecific competitive interactions, whereas LLB nesting territories did not differ significantly from random. Average interspecific NND for BE was 5.339 ± 3.719 m (SD) and for LLB 5.673 ± 3.931 m (SD). Only the LLB had a regular pattern, suggesting that LLB pairs take into account neighbouring BE active territories when establishing their own, while the opposite is not the case. Therefore, the LLB, which is the smaller of the two raptors, avoids BE nesting sites by placing its nests further than to conspecifics. NNDs in 2021 were lower compared to previous studies in Cyprus, in 2005 for LLB and 2009 for BE, indicating an increase in both species’ densities.