Thursday, July 31, 2008

Seeing Birds: A Yellow Warbler

Slowly I’m learning how to see birds. More and more I’m using habitat to tell me when I’m looking at a ‘different’ bird. This morning I looked out across my yard and saw a bright yellow spot moving around near the cattle-gate I use for access from the wide, willow-lined alley that leads to the river. The small bird was behaving more like a fly-catcher than one of the pretty little Goldfinches that frequent my sunflower feeders; sitting on a gate-rung, sallying up and out to catch an insect and returning to the same place. It was feeding low to the ground, but obviously fly-catching.

Grabbing my binoculars I could see it was probably a female Yellow Warbler (males, I’ve read, forage higher up than ground-level); I’d seen the pretty, belly-streaked males earlier in the season…but hadn’t actually noticed Warblers for several weeks.

I joined Cornell Lab’s ‘The Birds of North America…Online’ and have reading voraciously about all kinds of birds. This Yellow Warbler is a little ‘change artist’; it looks quite different depending on where they breed. The migratory Yellow Warbler common in North America has a yellow head; the non-migratory group of Mexico has the chestnut crown-patch pictured in this photo by Satish Nair (which one a calendar contest at the Galapagos Conservancy.) The other non-migratory group, which breeds in the tropics, has an all-chestnut colored head. Geographic variation in plumage is rather marked between groups, but generally more subtle within groups; but just to keep it fun, overlap in almost every character cited may be found in one population or another within each group! Ahhhhhhhhhh…birds! It’s all fascinating…for more information, I suggest you subscribe to Cornell’s website; the information is awesome.

Reading on, I suppose it is no surprise I have the Warbler’s here…apparently Brown-headed Cowbirds are especially fond of parasitic behavior towards them; laying their eggs in the Warbler’s nest. I had dozens of Brown-headed Cowbirds here earlier. The Yellow Warbler is apparently one of the few birds that can recognize its own eggs and sometimes knows when one is ‘different’. That Cowbird egg, while similarly spotted, is a lot bigger. This smart little Warbler has an interesting strategy for dealing with them, when they do notice ‘em; they merely build a new floor right over the Cowbird egg and raise the whole nest up…sort of encasing the parasite’s egg under the ‘false floor’, so that it would never hatch. They lay a new clutch and start over; one level up. Some Yellow Warbler nests become quite tall as a result of this behavior! Wild, huh?

Still, there can be dire results resisting the parasites; here is an astonishing article: "Mafia Cowbirds: Do they muscle birds that don't play ball?" by Susan Milius


Bosque Bill said...

Nice, sighting a Yellow Warbler! They supposedly breed down here in the bosque, but are not common. I've only once caught sight of one and judging from your post, it must have been a male as he was waaaaay up there in the top of the tree.

Fortunately, Brown-headed Cowbirds are not common down here. There were many more when I was in the SF Bay Area. One summer I spotted a little Wilson's Warbler working hard to feed what was obviously a cowbird fledgling. The "baby" was much larger than poor "mama." Made me mad, but there was nothing I could do.

Beverly said...

Hiya Bill! Yeah, I wonder just how many birds I miss because I don't pay attention to subtle differences, sometimes. I bet I missed a lot of Warblers... thinking they were finches. Heck, I only just barely made the Lesser Goldfinch! But, I'm getting better.

I just added a link (, in this post, to the Cornell page where I read that bit about feeding habits; let me know, if you don't mind...what kind of message you get if you follow the link (and if you're a member or not). I'm curious how the site will handle that.

For some reason, perhaps because I ran out of the white safflower seed and am back to pure black oil sunflower seeds, the grackles are back in droves...and black birds as well, it seems. I hope the dang Cowbirds don't show up too; I was mortified to discover how many were feeding in my yard. If you remember the hordes of icterids I had several months ago…you’ll understand why I quit feeding cracked corn. Besides, those pesky Eurasian Doves were getting a lion’s share, too. I’m going to pick up more safflower seed soon; those black and brown-type birds don’t seem to like it.

I’ve never personally observed a small bird feeding a cowbird fledgling; but I call it ‘The Baby Huey Effect’. It must look funny as hell, but just so sad, huh? Did you happen to follow the link at the end of the article? If the Warbler doesn’t ‘play nice’ with the evil Cowbird…they retaliate! Sheeshhhhhhhhhhhhhh It’s actually better if they do…something like 60% fewer warblers produced in nests where the birds resisted (in one way or another) the Cowbirds vandalism. Amazing.