The Unique Cowbird

Brown head cow birds are very common in the Midwest. They are nondescript, and blend in with the other birds in the area quite well. There is one thing about them that makes them very unique, they are parasitic birds. They do not make their own nests and they usurp the nests of other birds.

Definition of Usurp, a: to seize and hold (as office, place, or powers) in possession by force or without right.

Brown headed cow birds begin laying their eggs in the middle to late April. They typically stop in the middle of July laying eggs. Cowbirds typically lay about six eggs a day and wait a few days, and then start again. Usually only one Cowbird egg is found in each nest. It is very rare to find two cowbird eggs in one surrogate’s nest. It does happen if the nests to choose from are limited.

Female Cowbirds scout out nests in advance. They perch on shrubs or trees to watch for other birds building nests. They try to flush nesting birds by flying in and landing noisily in the nest they are hijacking. They tend to prefer species with eggs smaller than their own and in active nests with at least two host eggs in the nest. Cowbirds seem to prefer open cup nests and the nests of other birds that also lay speckled eggs. They also prefer to usurp bird nests that the mother bird is laying her eggs after sunrise. They are opportunists and will lay their eggs in none speckled eggs nests.

Brown-headed Cowbird eggs are usually oval, but the shape can vary to short, and rounded. The shell is moderately glossy., and is white or grayish white with dots and blotches also described as brown or chocolate in color. The markings are all over the egg.

Egg laying usually takes only 20 - 40 seconds. The female usually sneaks into the nest minutes before sunrise to quickly deposit an egg. The mother cowbird either eats a couple of the host’s eggs or drops them to the ground. If they are in a hurry, they will just break the shells of a couple host eggs so they don’t mature and are ejected from the nest by the surrogate mother at a later time.

The brown cowbird’s young typical grows much faster than the young of the nest their mother usurped. The stronger and bigger cow bird takes all of the food offered by its foster mother and the babies of the real mother grow weak and die and are pushed out of the nest. The surrogate mother raises the cowbirds like her own and completes the cowbird mother’s assignment.

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