Predator feeding ecology on Patagonian rocky outcrops: implications for colonies of mountain vizcacha (Lagidium viscacia)

On 10 rocky outcrops with mountain vizcacha colonies, diets and trophic relations of five predator species were analyzed to evaluate their impact in vizcacha populations. Diets included 17 prey items of which mammals represented 97% of biomass. Lagomorphs were the most important prey, followed by sigmodontines, tuco-tucos, and mountain vizcachas. The Barn Owl was a specialized predator, while the culpeo and lesser grison were generalized consumers. Predation of mountain vizcacha by Magellanic Horned Owls and culpeo foxes could increase vizcacha vulnerability because vizcacha populations are small and fragmented, and females produce only one offspring per year.     

Changes in the food of British Barn Owls (Tyto alba) between 1974 and 1997

Comparison of the results of a 1993–97 Barn Owl Tyto alba pellet survey with those of a similar survey from 1956–74 showed that Barn Owl diet had changed significantly. The primary differences were a widespread decrease in the percentage of Common Shrew Sorex araneus, combined with an increase in Pygmy Shrew Sorex minutus. The percentage of Wood and Yellow‐necked mice Apodemus sylvaticus and A. flavicollis and Bank Vole Clethrionomys glareolus in the diet also increased. Changes in Barn Owl diet since 1974 were independent of land‐class group, but were dependent upon region. This was due primarily to a large increase in the percentage of Apodemus spp. in Eastern England. Whilst the percentage of Pygmy Shrew in Barn Owl diet showed significant regional variation, there was no significant variation between land‐class groups. The diversity of Barn Owl diet increased between 1974 and 1997, although it was still lower in 1997 than earlier in the century. This increase was dependent upon region, but independent of land‐class group. The combined results of both surveys showed significant interland‐class group variation in dietary diversity. Changes in diet are discussed in relation to the intensification of agriculture and other changes in land management since the 1970s. The effects on Barn Owls of these changes in prey abundance are discussed, particularly in relation to the decline in Barn Owl numbers during the twentieth century.