Resumo

COZZANI, Natalia  e  ZALBA, Sergio M. Depredadores de nidos en pastizales del Parque Provincial Ernesto Tornquist (provincia de Buenos Aires, Argentina): importancia relativa bajo distintas intensidades de pastoreo. Hornero [online]. 2012, vol.27, n.2, pp.137-148. ISSN 0073-3407.

Nest predators in grasslands at Ernesto Tornquist Provincial Park (Buenos Aires Province, Argentina): their relative importance under different grazing intensities. Natural grasslands are facing a rapid reduction, mainly due to the advance of agriculture, cattle ranching and urbanization, and this has lead to the decline of many bird species. Ernesto Tornquist Provincial Park (Buenos Aires Province, Argentina) holds a population of feral horses responsible of an intense grazing pressure resulting in changes in the structure and composition of plant communities. During three breeding seasons we identified groups of nest predators associated to different grazing situations. We carried out artificial nest experiments using both Quail and plasticine eggs simulating clutches of grassland birds. Egg remains were compared with a reference collection in order to determine the group of predators that consumed them. From a total of 612 eggs used during the three years, 27.5% failed. In order of importance, nest failures were due to missing eggs, predation by large mammals, predation by small mammals, predation by birds, cattle trampling, consumption by unidentified predators, and predation by snakes. Predator assemblages would be different under different grazing pressure conditions, resulting in a differential effect on bird breeding success.

Palavras-chave : Artificial nests; Conservation; Grassland birds; Predation.

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