Raptor Entanglement with Human Debris at Nests: A Patchy and Species-Specific Problem

Abstract

Several species of birds, including raptors, add man-made objects, stones, greenplants, skins and dung of animals to build and decorate their nests. However, there is a compromise between the use of new nesting material and the increased risk of nestling mortality due to entanglement or ingestion of debris. Here, we present a compilation of cases of entanglement in raptors and specifically in a very common but poorly studied South American raptor. We observed the decoration in 86 of 95 (90,5%) nests of Southern Caracara (Caracara plancus) in an agricultural area of La Pampa province. Caracaras mainly incorporated agricultural twine in their nests and nestlings sometimes got entangled and died. We found 2 occurrences of entanglement during nine years of study. Decorating the nest, or at least to lean its interior with nylon twine, can impose a relevant death toll to Southern Caracaras, as has been found in other species elsewhere. Extension campaigns to reduce the misuse and the final disposal of debris materials such as baling twine in agricultural landscapes will be required to reduce this anthropic source of mortality in a species that although still common, is apparently reducing its numbers with the expansion of intensive agriculture.