Summer is a good time to study or just notice bird behavior. Parents are feeding young and the young are trying to find their independence. Newly-fledged birds tend to follow their parents, stopping close to them, furiously flapping their wings and uttering begging noises that say, feed me, feed me! As time goes on this behavior ceases as the juveniles become more confident and skilled at finding their own tasty snacks.
Yesterday as I sat on the deck watching for family feeding behavior I noticed a rather large fluffy bird sitting on the lawn. It was brown overall with a scaly looking back and light streaks below. Its appearance suggested a juvenile, but recently fledged, brown-headed cowbird. It was quiet at first glance, but in the next instant it began to loudly and continuously beg for food. I watched to see what would transpire. Was I correct? Was it a brown-headed cowbird or some other species?
Begging calls bring parents on the fly carrying food in their beaks for their babies. This scene was no exception. After a few loud begging calls a parent appeared with the desired snack in its beak. The parent was a beautiful dark-eyed junco. Its jet-black hood indicated that it was a male Oregon junco, one of the four Northwest subspecies of the dark-eyed junco. The baby it was feeding was much larger than it. To be sure, it was definitely a recently fledged brown-headed cowbird. I was right!
Brown-headed cowbirds never build a nest. Instead they lay their eggs in nests of other birds, especially those that are smaller than themselves such as such as the song sparrow, white-crowned sparrow, yellow warbler and the dark-eyed junco. According to the Cornell ornithological lab, the cowbird parasitizes over 140 host species, some of which are even larger than the adult cowbird. Scientists have also determined that a single female cowbird is capable of parasitizing 30-40 nests over the breeding season because she can lay more eggs than any other bird species.
Cowbird eggs hatch in 10-12 days, whereas those of the host usually take around 17 days to hatch. This gives cowbird babies an advantage over the host's babies. Cowbird babies are larger and more demanding so they get the bulk of the food their foster parents bring, starving the other nestlings. In addition, they literally may crowd the smaller nestlings right out of the nest, and they have even been known to roll the host's eggs out of the nest. All is not lost, however, because some host birds recognize the cowbird egg and either remove it or cover it with nesting material. Other tactics include delaying nesting or nesting earlier then the cowbird's breeding season.
The brown-headed cowbird feeds on the ground and prefers invertebrates, grains, seeds and fruits. It also enjoys coming to feeders. It is a common, permanent resident of the Peninsula and the Willapa National Wildlife Refuge. Cowbirds can be seen on lawns, in fields, and around cattle. If you see a bird such as a dark-eyed junco or a white-crowned sparrow feeding a bird much larger then itself, you can be pretty sure it is feeding a baby brown-headed cowbird!
"Common Birds of the Long Beach Peninsula," by Kalbach and Stauffer, is available from the Chinook Observer, Bay Avenue Gallery, Time Enough Books and the Long Beach Peninsula Visitors Bureau.