HOW DO BROWN-HEADED COWBIRDS (MOLOTHRUS ATER)CAUSE NEST FAILURES IN SONG SPARROWS (MELOSPIZAMELODIA)? A REMOVAL EXPERIMENT

Brown-headed Cowbird (Molothrus ater) Science Article 8

abstract

A removal experiment was conducted to measure how much and by whatmechanisms brood parasitic Brown-headed Cowbirds (Molothrus ater) cause nest failures in acommonly used host, the Song Sparrow (Melospiza melodia). When numbers of female cowbirdswere reduced experimentally, nest failures fell from 65.0% (n = 663 nests) to 49.9% (n = 331).Cowbird reduction reduced the frequency of nest failure to one-third of control levels in SongSparrows during the last 80 days of the sparrow’s breeding season, the period when most parasiticlaying took place.

JAMES N. M. SMITH et al., The Auk 120(3):772-783, 2003

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