Monday, April 17, 2006

Raptor Tales

The bald eagle population in the Chespeake region appears to be getting a little crowded. The fight that injured Martha, one of the pair of eagles that has nested at the Wilson Bridge, was most likely a battle for the nesting territory with another female. The eagle population has expanded greatly in the region since the species' brush with extinction, and most of the best habitat is already taken.

The nonprofit Wildlife Center of Virginia in Waynesboro treated six eagles last year that had wounds consistent with fights with other eagles, compared with two the year before, said its president, Ed Clark. At Tri-State Bird Rescue & Research in Newark, Del., another nonprofit facility, the bald eagle injured near Washington was the fifth one brought in this year from Maryland with fight injuries.

"All of this relates to the fact that the population is reaching some level of capacity at this point," said Bryan D. Watts, director of the Center for Conservation Biology at the College of William and Mary. "The bay population has increased tenfold in the last 30 years. It doesn't take that many years to go to saturation. The bay has produced more chicks in the past five years than it has in the previous 25."

Maryland stopped doing annual eagle-nest surveys in 2004 because the population had met recovery goals, but Glenn Therres, associate director for wildlife at the state Department of Natural Resources, said he believes the number continues to grow. Birds are nesting in new territories -- last year, for instance, breeding pairs settled in two mountainous western Maryland counties for the first time in recent decades.

In prime habitats such as those along the Potomac River, eagles are "packing in denser" than biologists had thought possible, occupying nests every mile or two. In the 1930s, Therres said, biologists recorded that eagle nests were generally three miles apart. This trend "may be an indication that we are getting close to carrying capacity," he said.

While eagles in the Washington region have tolerated the large human population fairly well, peregrine falcons seem to thrive on manmade structures. Many nests in Maryland and Virginia are located on bridges, including one on the Wilson Bridge. The high structures approximate the falcons' natural habitat on mountains and cliff faces, and the urban location provides plenty of easy prey, especially tasty pigeons. Wildlife biologists are concerned about chicks drowning in the river when they learn to fly; other hazards include raccoons, which may prey on eggs. Attempts have been made to encourage falcons to nest in the mountains instead of bridges, but for now at least, the falcons seem to prefer the bridges.