The effect of nest usurpation on breeding success of the black-billed magpie Pica pica

Magpie (Pica pica) Science Article 4

abstract

The breeding of some birds, such as raptors or owls that do not build theirown nest, is often limited by the availability of nests constructed by otherbird species. When breeding habitats substantially lack natural nest sites(e.g., cavities in trees or cli
s), a strong conflict over the nest site can occurbetween raptors and other birds breeding in the nests suitable also forraptors. The nest site selection of the Eurasian kestrel (Falco tinnunculus)was studied in an extreme situation when nests of the black-billed magpie(Pica pica) served as the only suitable nest sites for kestrels. It was foundthat 42% of new magpie nests were usurped and 30% of old nests were occupied(re-used) by raptors, mainly by the kestrel. The nest height above theground was the main predictor of nest usurpation. Other variables, such aslaying date, nest volume or perimeter of the nest tree were not signi cantpredictors. A tendency to build nest sites closer to the ground observed withan advancing breeding season may therefore represent a strategy of magpiesto override nest usurpation. Nonetheless, while the magpie pairs nesting inlower heights were more likely to escape from nest usurpation, they su
eredfrom a higher, though not signi cant, predation rate relative to the magpiesnesting in higher positions. Three possible hypotheses which can explain whykestrels and possibly other raptors have a tendency to take over new nestsrather than to occupy old ones are discussed.

Prokop, P, Biologia, Bratislava 2004, 59: 213-217

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