Yellow Warbler and Cowbird, Arapahoe County

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bunting...@gmail.com

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Jun 27, 2016, 1:49:29 PM6/27/16
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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

Jim Nelson

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Jun 27, 2016, 2:20:25 PM6/27/16
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Brian,
 
It is interesting to see how many different species raise Cowbird chicks.  According to the species account in Birds of North America Online, one comprehensive source found that Yellow Warblers are the most frequent host species for Brown-headed Cowbirds.  At home here in Maryland, I see Song Sparrows (which are the number two most frequent host species) feeding Cowbird chicks in our yard every summer. 
 
The largest size disparity I have ever witnessed was a tiny Ruby-crowned Kinglet feeding a significantly bigger Cowbird chick in Rocky Mountain National Park.
 
Jim Nelson
Bethesda, Maryland
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Scott Somershoe

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Jun 27, 2016, 2:38:16 PM6/27/16
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Yellow warblers are well documented for recognizing a cowbird egg in their nest. They will build a new nest on top of the nest with the cowbird egg.  I've seen photos of 4 or 5 complete nests in a stack.  That's one way to not raise any cowbird young, but maybe not raise any of your own either!  They obviously raise cowbird chicks now and again though.

I saw Blue-gray Gnatcatcher feeding a cowbird chick on Jekyll Island GA many years ago.  Just about as big of a disparity as a kinglet.

Scott Somershoe
Littleton CO


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Nick Komar

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Jun 27, 2016, 4:27:21 PM6/27/16
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This cowbird chick was being raised last week by Gray-headed Junco in the hills west of Fort Collins. image1.JPG

Nick Komar
Fort Collins CO

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Charles Hundertmark

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Jun 27, 2016, 5:35:07 PM6/27/16
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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

Tom Behnfield

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Jun 27, 2016, 6:19:48 PM6/27/16
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Last friday, Art Hudak & were at Genesee Mountain Park (Jefferson County,) and we too saw a Dark-eyed Junco feeding a BHCO chick.

Good birding!

Tom Behnfield
Lakewood, CO

Terry Hunter

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Jun 27, 2016, 7:08:36 PM6/27/16
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You both may already know the info in the below Cobird (bird postings in CO) emails. I did not know the #1 and #2 host species for Cowbirds were the Yellow Warbler and Song Sparrow. Yipes!


On Jun 27, 2016, at 12:20 PM, Jim Nelson <kingfi...@verizon.net> wrote:

Terry Hunter

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Jun 27, 2016, 7:14:03 PM6/27/16
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Sorry meant to send this email to someone else!
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