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

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.

Keywords

• tree height
• bare ground cover
• Spur-thighed tortoise density
• predation
• conservation