FORT SILL, Okla. -- The brown-headed cowbird is one of those native birds that wasn't raised with good manners. And that's a problem for the black-capped vireo.
You see, the vireo is an endangered species, for reasons given in a companion article (on page 5A). But cowbird females just do what they were programmed to do and that is to lay their eggs in the nests of other birds instead of setting up housekeeping themselves. They're awfully sneaky about it. They stake out a nest and time their egg-laying so that their baby either hatches first, or is just bigger and more aggressive than the rightful occupants of the nest.
Unfortunately, the surrogate parents don't realize that big gaping mouth is that of an imposter. They are programmed to stuff bugs and worms into it. The cowbird baby either suffocates, pushes out, or out-competes the smaller babies and becomes the only mouth the parents have to feed.
I've seen warblers feeding a greedy cowbird baby twice its size. I had a cardinal in my yard a few weeks ago feeding a cowbird chick while its own presumably died. It makes me sad.
Even worse, a female cowbird can lay 40 or more eggs in a season, and most songbirds might raise four to eight of their own progeny in a season. Most songbird species can handle this ill-mannered invasion. But not the black-capped vireo, which has a very limited breeding range.
So on Fort Sill, the cowbirds are trapped in the areas close to where the vireos nest. Kevin McCurdy, who retired in 2012 as Fort Sill's wildlife biologist, works as a contract employee for Gulf South Research Corp., and his sole job is to trap and dispatch the brown-headed cowbird.
Three days a week he checks the walk-in cages scattered in 25 locations, most of them near lakes and ponds. If species such as cardinals or house finches are trapped, they are set free. Five male and two female cowbirds are left in the cage as decoys, with plenty of sunflower seed and fresh water. Birds find their way in from a large opening in the top that leads to several smaller openings. They can get in, but can't figure how to get out. Pretty clever, huh?
McCurdy generally starts his rounds at 6:30 a.m. and keeps meticulous records of the number and species of birds trapped. He said the first two weeks saw a record catch of about 1,100 cowbirds. Last year only about 500 birds were trapped in the entire season, which runs from April to June.
What happens to all those unfortunate cowbirds? "I pop their necks," said McCurdy. Ulp.
I had some banty chicks once, and when I started my first winter job at Big Bend National Park in Texas, I had a house-sitter take care of them. When I returned, some of those cute little chicks were mean little roosters. When one went after my bare ankle in the yard (I let them roam free during the day) I picked him up by his scrawny neck and told him how easy it would be to snap it. It didn't change his attitude one bit, and the others were just as bad. A friend who was raised on a farm told me that one way to kill the roosters was to put them in a pillowcase and run the car exhaust into it. I just didn't have the heart to kill them no matter what the method. However, I was lucky.
The first night after my return, all of the chickens went into their summer roost which didn't have the screen door on it yet. The next morning there were six piles of feathers in the yard. Foxes took care of my problem (and a hen or two as well.)
I don't know how McCurdy does it. But it's just as necessary as any other wildlife management tool. Cowbird populations are large and healthy, and humans have given them more opportunity to thrive. They follow bison and cattle because they stir up insects as they walk. Texas and Oklahoma have a lot of cattle.
The black-capped vireo populations haven't fared as well. Fortunately, with the cowbird trapping program, their numbers have soared compared to what they were in the 1980s. The Wichita Mountains Wildlife Refuge now has approximately 4,300 breeding pairs of vireos.
Since the males do the singing, they're more easily seen than the females. They are also quite handsome, with black heads, white spectacles, and an olive green back. The red eyes are noticeable when the sun hits them right.
Their songs are distinctive and variable, and you can listen to variations on several of the bird apps I've talked about in this column. Or visit the Cornell Lab of Ornithology website AllAboutBirds.com to listen. As with many birds, you'll generally hear far more than you see.
Count yourself fortunate if you do see a male singing, because our part of Oklahoma, parts of Texas and Mexico are the only places they breed. I've seen and heard several at the refuge. One near the Quanah Parker Lake boat landing became #460 on my life list.
Go now if you want to see them. Plus the wildflowers there are downright gorgeous.
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