City - Palo Alto State - CA Country - United States
About
Molothrus ater- #164 BHCB once followed bison herds across the Great Plains (now they follow cattle) and their nomadic lifestyle made it impractical to construct and tend to nests. Their successful alternative was the adoption of the deceptive ar of "nest parasitism": laying eggs in the nests of other sonbirds. Over the ages, this strategy has proven to be effective for cowbirds, because many of the parasitized adultsongbirds will incubate the cowbird eggs and raise the cowbird chicks without distinguishing them from their own. Hatching in as little as 10 days, nestling cowbirds outcompete their foster siblings. Fledging at nearly adult sixe, a juvenile cowbird continues to beg after eaving the nest, often dwarfing a Wrentit or Common Yellowthroat that is popping goodies into its gasping mouth. The expansion of ranching, the fragmentation of forests and the increase of transportation corridors has significantly increased the cowbird's range. The cowbird now parasitizes more than 150 bird species in North America. Taken from: Birds of Northern California, Fix and Bezener, 2000.
An event mentioned by Miyoko Chu on her excellent book- Songbird Journey is that, in Ontario, cowbirds laid eggs in 41% of yellow warbler nests. If a yellow warbler notices cowbird eggs mixed in among her own, she may abandon the nest and start over elsewhere, or bury the eggs on top. One yellow warbler buried cowbird eggs five times, building a six-tiered nest with a total of eleven cowbird eggs sandwiched in between.
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