評論
打印
Chimney Swift Bird Numbers Declining
People across the United States are putting up tall, narrow structures to help a little bird called the chimney swift. They hope the birds will use these structures as nesting areas and resting places.
Chimney swift numbers are decreasing as the shape and design of the nation's buildings change. People are tearing down old factory buildings and schools. Many of these structures have chimneys -- enclosed structures or pipes that release smoke into the air.
Today, most American homes do not have chimneys. And many homeowners who do have chimneys cover up the top to keep animals out.
Chimney swift numbers have fallen by more than 70 percent since the 1960s, scientists estimate, and by more than one-third over the past 16 years.
That large drop led the International Union for the Conservation of Nature to declare swifts as "vulnerable." That is the last step before they are considered "endangered."
Building take chimneys and towers
Bird lovers are building chimney-like birdhouses as summer homes for swifts. Several are set up around the city of Birmingham, Alabama, where Greg Harber has been watching the birds for almost 10 years.
"It does give us hope that if we put them up ... they will use them," Harber said as swifts flew close to a real chimney.
Georgean and Paul Kyle often get credit for starting the current interest in building towers. The Kyles told The Associated Press in an email that they have put up more than 100 nesting towers in Central Texas.
Eighty percent of those built before the birds' March arrival get nests their first year.
Hundreds of migrating swifts make use of two of the 6.1-meter-tall towers, the Kyles said.
Jim Bonner is director of the Audubon Society of Western Pennsylvania. He says his group has built or helped with about 150 towers in Pennsylvania.
Why have chimney swift numbers declined?
But the link between the drop in chimney swift numbers and chimney loss is not clear. The flying insects that swifts eat also appear to be declining.
University of Connecticut professor Margaret Rubega thinks the cause of the birds' decline could be in South America.
"Chimney swifts are fundamentally a South American bird that visits North America for four months," she said.
Rubega said a big problem is that scientists have only a few reports of small numbers of chimney swifts in the upper Amazon Basin. So, they do not really know where the little birds spend the winter, let alone what may be happening to them there.
However, three less common western species of swifts also migrate to Central or South America. Their numbers are unchanged or even increasing somewhat.
I'm John Russell.
