Holidays for humans disrupt home life for eagles

http://www.cnn.com/2000/NATURE/03/07/bald.eagle.enn/index.html:

By Environmental News Network staff

March 7, 2000

Web posted at: 11:46 a.m. EST (1646 GMT)

As the Alaskan wilderness becomes a

hot spot for Americans on holidays,

their recreation is wreaking havoc on

the home life of bald eagles, according

to a recent study.

Human activity that occurs near eagle nests causes a striking change in the way

adult eagles behave, the researchers found.

"We're used to looking at the large visible effects that humans have on wildlife

such as logging or draining wetlands," said Robert Steidl, a professor of wildlife

at the University of Arizona. "Subtle impacts [from recreation] may be just as

consequential."

Steidl and Robert Anthony of Oregon State

University examined the effects of increased

recreation on bald eagles living along the Gulkana

National Wild River in south-central Alaska.

Managed principally for wilderness recreation, the Gulkana River is one of few

wilderness rivers in Alaska that is accessible by road. As a playground for

whitewater rafting, fishing and hunting, the area attracts more and more visitors

each year.

Nearly all of the human activity in the

area occurs along the river in close

proximity to eagle nests, so Steidl and

Anthony set up their study there.

The researchers examined the nesting

patterns of eagles over 48-hour periods

for four years. "We acted as low-impact

campers," Steidl said.

Steidl and Anthony charted the time

adult eagles spent brooding and feeding

their young, maintaining their nests,

preening, perching, sleeping and conversing.

Adult eagles decreased some activities by as much as 59 percent per day when

humans were near. The amount of time nesting areas were left unattended

increased by 24 percent.

Some of these behavioral changes may have direct effect on the survival of

nestling eagles, the researchers note. When humans were near the nests, the

amount of prey consumed by the eagle chicks decreased by an average of 29

percent per day. The number of feeding rounds at the nest decreased by 20

percent per day.

"Nestlings probably suffered the highest

energetic costs from disturbances

because of their dependence on adults

for food," Steidl said.

The long-term consequences of human

encroachment are cause for great

concern. Growth rates of the raptors

could be retarded and the birds' survival

strategies could be impaired, the

researchers say.

The researchers recommend restrictions

on use of the area.

"Behaviors such as those observed during our study provide a useful and

sensitive tool for gauging the effects of recreational activities on wildlife," Steidl

said. "If bird behavior can be carefully quantified, then management strategies

can be developed before these and other potentially harmful activities result in

long-term negative consequences to bird populations."