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their young until they are old enough to look after themselves. Certain birds, known as “brood parasites,” however, lay their eggs in the nests of other birds and have no social family life with their own offspring.
The sparrow was obviously a victim of an adult cowbird that threw out the sparrow’s eggs and deposited its own. •
Cowbird parasitism involves a lot of scouting. Probably for this reason, cowbirds are among the early arrivals during spring migration. Typically, the female watches a smaller bird build its nest. Then, usually in early morning under dim light, she visits her victim’s nest when the nest-builder is absent.
The visit is made after a host bird laid eggs but before it has begun incubating its own eggs.
The female cowbird lays her egg quickly and leaves, returning later to destroy at least one of her host’s eggs by jabbing it with her beak and flying away with it. She is able to distinguish between her own eggs and host eggs.
About half of all host species tolerate the cowbird’s white with brown speckled egg, incubate it and raise the cowbird nestling as if it were its own offspring.
Since cowbird eggs hatch more quickly than most host eggs and
96.9%