Influence of Habitat and Food Resource Availability on Common Raven Nest Site Selection and Reproductive Success in Mediterranean Forests

Simple Summary A central goal of life history studies is documenting traits related to reproduction. Bird nest selection is influenced by the abundance of food resources and determines reproductive success. In Mediterranean forests threatened by human influences and by global change, studies of Common ravens are limited, despite this generalist species being able to exert strong pressure on targeted species such as the Spur-thighed tortoise. Our study demonstrated that (i) tree height, the absence of vegetation cover and the abundance of tortoises influences the selection of raven nest sites; (ii) that the spatial distribution of raven nests is clustered; and (iii) that young tortoise abundance plays a part in raven reproductive success. We discuss in depth how the key structural elements and resources of the forest might affect the interaction between the population dynamics of Common ravens and sensitive species on which they prey. Bearing in mind the positive increase in the number and distributional range of Common ravens, we recommended conducting long-term studies of reproductive parameters and appropriate conservation actions.Abstract Bird nest selection in forests can be influenced by the composition of key structural elements and resources. This has important consequences in terms of species population dynamics since it can determine reproduction success. Here, we assessed Common raven nest-site selection and reproductive success, and how these might be determined by foraging behavior and habitat structure. A previously documented breeding raven population that exerts high predation pressure on young Spur-thighed tortoises (Testudo graeca) in a Mediterranean forest was monitored. Generalized linear mixed models were performed to determine the singularities of the trees with nests and the drivers of reproductive success of breeding pairs of ravens. The results showed a high density of breeding pairs in the study area (0.8 pairs/km2), which selected taller trees in areas with higher bare ground cover and a high density of tortoises for nesting. Nests were spatially aggregated; breeding pairs occupied smaller territories and intraspecific competition seemed relaxed, reflecting the abundance of food resources. Most breeding pairs occasionally predated on young tortoises. Tortoises seem to play a part in raven reproductive success in our study area, which might be associated with the availability/catchability of young tortoises. The study illustrates that Spur-thighed tortoise distribution and abundance plays a role in the breeding behavior of ravens and is mediated by habitat structure. Understanding the drivers of nest-site selection and the breeding behavior of ravens is pivotal to implementing appropriate habitat management and conservation strategies across their distribution range, particularly in areas where ravens potentially affect threatened species.