Landscape and anti‐predation determinants of nest‐site selection, nest distribution and productivity in a Mediterranean population of Long‐eared Owls Asio otus

Abstract

Nest predation is an important determinant of owl breeding success. We studied Long‐eared Owl Asio otus productivity and attributes of nest‐sites at the microhabitat and landscape scales in a Mediterranean locality over an 8‐year period. We examined the effect on nest location and productivity of protective cover in concealing the nest from aerial and terrestrial predators. A dense cover of ivy and tree‐foliage at canopy level favoured nest location but not productivity. By contrast, high shrub cover beneath the nest was selected by Owls and was positively related to both the site reoccupancy rate and the overall number of young fledged. Pre‐fledging Owls use the ground, where they are exposed to terrestrial predators, which are much more abundant in the study area than are aerial predators. Our results therefore support the hypothesis that Owls adapt nest‐site choice to local sources of predation risk. As reported elsewhere, Long‐eared Owls in our study area showed restricted territoriality and nested in clusters. As active nest‐sites during the same breeding season were more than 1 km apart on average, and their productivity was never greater for clustered nests than for more isolated nests, nest aggregation could not be interpreted as a case of facultative colonial breeding, which has been reported for this species in other areas. Neither landscape variables indicative of the availability of foraging areas nor structural attributes that protect young from predators explained the remarkable scarcity of nests in half of the study area. Unmeasured factors such as human disturbance could explain the pattern of distribution of Long‐eared Owl nests.

Breeding Performance of the Grasshopper Buzzard (Butastur rufipennis) in a Natural and a Human-Modified West African Savanna

“…Although we recorded little direct evidence of predation by avian predators, the canopy cover shielding the nest from the sky, and thus avian predators (Tome 2003, Rodríguez et al 2006, was positively associated with nest success and fledgling number. This suggests that Grasshopper Buzzards could escape detection and predation by avian predators by improving nest concealment.…”

“…While breeding, Grasshopper Buzzards consume a wide variety of vertebrate and invertebrate prey (Buij et al 2013), the activity and availability of some of which (e.g., amphibians, insects) increase with rainfall, potentially reducing the need for long-distance foraging flights (Selås 1997). The success of raptor nests may be strongly influenced by natural predators and structural characteristics of the site that increase concealment from avian and mammalian predators (Tome 2003, Rodríguez et al 2006. Natural predation is likely to be important in protected areas, which provide refuges for carnivores (Blaum et al 2007) and large raptors (Thiollay 2006(Thiollay , 2007, whereas anthropogenic disturbance and nest harvesting are likely to be more important in agro-ecosystems (Virani and Harper 2009).…”

Density, diet and productivity of Long-eared OwlsAsio otusin the Italian Alps: the importance ofMicrotusvoles

“…However, in the initial years of the study it became clear that many nests were extremely well hidden and inconspicuous, and in some cases fledglings were observed where no nest had been previously found despite a pronounced field effort (Rodríguez et al 2006). Therefore, to assess breeding output, territories were repeatedly visited during April-June to listen for the persistent food-begging calls of fledged young.…”

Demography, breeding success and effects of nest type in artificial colonies of Red-footed Falcons and allies

“…This species is the most common nocturnal avian predator in the region, therefore it is unlikely that local population size is causing the observed pattern. Long-eared Owls are restricted territorial breeders, and may often breed in clusters (Rodriguez et al 2006), thus intraspecific exclusion may have a smaller role in regulating breeding numbers at our colonies. Moreover, these birds are often the first to commence breeding at our study site (pers.…”