We documented effects of Brown-headed Cowbird (Molothrus ater) parasitism on Chipping Sparrows (Spizella passerina) in southwest Colorado. Overall, 17 of 77 nests (22%) were parasitized. Abandonment was significantly higher among parasitized nests (29%) than unparasitized nests (5%). More Chipping Sparrows hatched and fledged per unparasitized nest than per parasitized nest. Reduction of host hatching and fledging rates in parasitized nests was attributable to smaller clutch size and higher abandonment. The major source of nest failure was predation, not parasitism; overall, 53% failed from predation, and only 6% failed from parasitism. There were no differences in weight, ulna length, tarsometatarsus length, or length of outermost primary between sparrow nestlings in parasitized and unparasitized nests. Only 18% of cowbird eggs laid resulted in a fledged cowbird. We observed no differences in nest placement or nest concealment between unparasitized and parasitized nests.
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1 February 2001
EFFECTS OF BROWN-HEADED COWBIRDS ON THE NESTING SUCCESS OF CHIPPING SPARROWS IN SOUTHWEST COLORADO
Catherine P. Ortega,
Joseph C. Ortega
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The Condor
Vol. 103 • No. 1
February 2001
Vol. 103 • No. 1
February 2001
abandonment
brood parasitism
brown-headed cowbird
Chipping Sparrow
Molothrus ater
nest concealment
Spizella passerina