Updated: Jul 22, 2020
Recently, my girlfriend and I were walking and bird-watching on the UC Berkeley Campus here is Berkeley, and we saw a group of Oregon Juncos with their babies exploring some bushes. One of the babies, however looked far too big to be a Junco. I instantly thought "is that a cowbird?"
Brown Headed Cowbirds are what is known as a brood parasite. The females lay their eggs in the nest of a host bird, and that host, in this case a family of Oregon Juncos, raises the baby cowbird as if it were one of its own. I have seen Cowbirds occasionally in California, but they are not super common here, and I had never seen a baby with its host family. This was a first for me, and an incredible sighting. I know that in some cases, the baby Cowbird will out-compete the host babies for food, or even push the host babies out of the nest, but that did not appear to be the case this time. The Oregon Junco in the foreground of this photo appears to be a juvenile.
The Cowbird and its "siblings" were old enough to feed themselves, but still begging their parents for food. As we watched, the Juncos even began to move on without the baby Cowbird. Soon, it will molt out its baby feathers, and its beak will turn black. If it is a male, it will have black feathers with a brown head, and if it is a female, it will be all brown.
For more information, check out the Cornell Birds Page.