Thursday, August 23, 2007

Cowbirds & House Sparrows

I've always known I value some birds more than others. After living in the Austin area these last 37 years, I don't particularly value grackles. They've over populated, they fill the trees and utility wires, they are loud and they are very adept at surviving the urban landscape. Pigeons are another example. I actually think pigeons are beautiful birds with their irridescent feathers. But I can understand why people grow to hate them. My son's condominium porch was unusable because of the constant pigeon droppings from their perch above. Pigeons are great scavengers of the crumbs around restaurants. People living near the coast often view sea gulls as nuisances as they swoop in to find their tasty morsel off your plate in outdoor eating establishments. Signs abound - Don't feed the birds!While I find their call to be a pleasant reminder that I'm at the coast, they are certainly noisy birds. Of more concern is their aggression to other species. There are several species fighting for survival because the gulls raid the nests as part of their diet.

Starlings and house sparrows are of particular concern because they are not native to North America. Starlings were brought over by someone who wanted to introduce all the birds that were written about in Shakespeare's work. In retrospect, this was a lousy idea because starlings lay their eggs in other bird's nests. The starling babies are usually larger than the original babies and thus are able to get the food leaving mother bird feeding the starlings rather than her own babies.

Two hundred years ago there were no house sparrows in North America. Today they are one of the most abundant songbirds found in all of the 48 contiguous states. The first attempts to bring them over from Great Britain and release them in New York City were unsuccessful. However, continuing efforts in many places led to the great numbers found today. While they were brought in to control insects, they are actually seed eaters. And sadly they are in direct competition for resources for native songbirds. While sparrows are not the only cause of the declining songbird populations, cavity nesting species such as bluebirds and tree sparrows have taken big hits as the house sparrows range increased. House sparrows are particularly agressive to bluebirds killing both the babies and the parents.

Cowbirds are another problem species. While native to North America, they originally followed the large buffalo herds eating insects stirred up by the bison's hooves and grass seed. When the large herd disappeared they found domestic cattle. As Americans cleared forests to create cropland and pastureland, the cowbirds habitat grew. So, you may ask, what is the problem here. Cowbirds are parasitic. They don't build their own nests and raise they young - they lay their eggs in other bird's nests delegating all of the parenting duties to some other unsuspecting bird. And while you would think that these other birds would reject the odd bird in their nest, over 150 host species have successfully raised cowbird babies.

While part of me shudders at trapping and dispatching (euphemism for killing) these birds, I can see the real issues here. Cowbirds contribute to the decline of two species in my area - the black capped vireo and the golden cheeked warbler. Cowbird control may make the difference between whether these species survive or fade into extinction. Preservation of their habit is also critical for their survival.

My husband wrote a story about the demise of the passenger pigeon. Passenger pigeons were once the most numerous bird on earth. Because of their roosting patterns - hundreds of birds in one tree, they were easy to hunt. Between the hunting and loss of habitat as forests were cleared for farming, the birds declined. And apparently they needed the large flocks to survive, because the species declined rapidly and the last bird died in 1914.

Do we need to control the populations of these "pest" birds? Absolutely! But I certainly hope that as humans we are older and wiser such that in controlling the populations so that other birds will thrive, we pay attention to the populations of the birds we are "controlling" so that they do not become extinct when we aren't watching. Thankfully, we track bird counts much more carefully now so hopefully, we will be wise in our efforts to promote bird diversity.

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