Holidays for humans disrupt home life for eagles

Wildlife researchers attach a radio transmitter to a male bald eagle

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."

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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.

The Gulkana National Wild River in Alaska is popular destination for river rafters.

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.

A bald eagle roosts next to the Gulkana River in Alaska, the site of a four-year study.

"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."

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