August 24, 2013 / Leslie

Weekend Birding: Who’s Your Daddy?

Birds, Brown-headed Cowbird, Photography, Photos

This is a Northern Cardinal feeding a recently fledged Brown-headed Cowbird. Why? Because a female Cowbird substituted one of her eggs for a cardinal egg when no one was minding the nest.

The cardinals raised this chick as one of their own and didn’t seem to notice that it doesn’t remotely resemble a young cardinal. (While Mr. Cardinal was feeding the cowbird his own son/daughter was hiding in my apple tree and then emerged to sit on the back fence.)

Brood Parasites

Cowbirds do not build nests or raise their own young. Instead, they lay their eggs in the nests of other species hoping that bird will rear their young. Over 144 species have been documented as cowbird foster parents.

Female cowbirds spend their days stalking other birds to locate their nests. When they find one they will toss out one of the host’s eggs and quickly replace it with one of their own. Many birds never notice the difference. Some birds do notice and will abandon the nest or build a new nest on top of the old one, and others may eject the offending egg.

Adult Female Cowbird

The female cowbird remembers where she has deposited her eggs and periodically returns to check on them. If her egg is missing she may lay another one or, if the host’s eggs are too close to hatching, or perhaps in a fit of revenge, destroy the nest forcing the host to build a new one. This mafia-like behavior was actually documented in a scientific study.

Cowbird young have a short incubation period usually hatching a day or two before the bird’s own young. They also have a voracious appetite and grow quickly often to the detriment of the host’s young. We like to think that the parents provide the same amount of food to each of their nestlings, but that is not the case. They feed the baby who opens his mouth the widest and this is often the large cowbird. The cardinal host parents in my yard were also able to raise one cardinal, however a normal, non-parasitized, nest would have produced three or four cardinals.

Adult Male Cowbird

Interesting Facts:

Cowbirds are promiscuous, there is no pair bond. Males and females have several different mates within a single season.
A female can lay 35 to 40 eggs per nesting season.
Cowbirds will lay eggs in the nests of more than 220 species of birds.
It is theorized that cowbirds became parasitic because at one time they followed roving herds of bison and had no time to stop to nest.
Cowbirds can be found across most of North America.
Cowbirds do not “imprint” on their foster families and will join up with a flock of other cowbirds after a few months.

Saturday Snapshot was originated by Alyce at At Home With Books. For the summer it will be hosted by Melinda of West Metro Mommy. Visit her blog to see more great photos or add your own.