Re: [cobirds] Yellow Warbler and Cowbird, Arapahoe County

Although I've seen species as large as Red-winged Blackbird parasitized by cowbirds, I've been amazed at how often the victims are much smaller species. Several years back while atlasing in northern New Mexico, I often found Blue-gray Gnatcatchers and Virginia's Warblers feeding young cowbirds.During the second Colorado Breeding Bird Atlas, I photographed a female Ruby-crowned Kinglet repeatedly stuffing extremely small bugs into the gaping mouth of a begging cowbird. The kinglet's head nearly disappeared in the mouth of the cowbird chick.

Chuck Hundertmark

Lafayette, CO

On Jun 27, 2016, at 11:49 AM, buntingrobinjay@gmail.com wrote:

Today while walking along my favorite part of the Mary Carter Greenway I encounter an odd looking bird that I could not figure out. It was all brown with fine streaks along the breast and belly but the bill was wrong for a finch and it was too big. Then I noticed it was flapping around from branch to branch frantically, and I noticed it was chasing a yellow warbler male and constantly calling. I could not make sense of why this bird would be chasing a warbler and calling like that. Finley both stopped on a Russian olive branch and I was able to get a better view. I observed the warbler glean an insect (likely a gnat) and take it lower down to the unknown bird and stick it in the bird's mouth. It finally came together then. This was a recently fledged juvenile brown headed cowbird that the warbler believed to be its offspring. It was certainly dwarfed by the cowbird. I have not seen this in the wild before, I have one nature programs but that was it. Interesting behavior to watch, not all that good for the warblers however. Hopefully their population will not be to affected by this along the river. This was at the mile marker 12, the dirt walking path goes through some woods that is a favorite for warblers and other birds. Thought I would share this.

Brian Johnson

Englewood CO

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