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smaller birds are the most frequent targets, baby cowbirds are usually much larger than the host’s own babies. When possible, the baby cowbird tosses at least one of the host’s young out of the nest, ensuring it will get more food.
Some birds will not tolerate a cowbird egg. The Gray Catbird and American Robin, for example, throw out cowbird eggs. Others bury the cowbird egg and their own first egg or eggs by building another nest floor over the eggs. Other species, such as the Northern Cardinal, simply desert parasitized nests.
Birds most frequently parasitized by cowbirds include all species that nest in open trees, bushes or on the ground. Hole-nesting species like Woodpeckers, Chickadees and Eastern Bluebirds are seldom victims.
While cowbirds are the only North American parasitic birds “obliged” to parasitism as a way of life, there are many other species that habitually lay their eggs in other birds’ nests. Starlings, sparrows and some finches all victimize other birds.
Care that the hosts provide to the young parasites is care denied to their own young, with the result often being detrimental on the reproductive success of the nesting hosts and may affect their population num
95.9%