Hawkwatch Sees Numbers Rise

Endangered peregrine falcons, decimated by the spread of the pesticide DDT beginning in the 1940s, appear to be rebounding in the West.

The numbers of two other migratory birds of prey, or raptors - merlins and osprey - appear to be increasing, Steve Hoffman of HawkWatch International said.

North Idaho has been registering the increases for 15 years, said Jim Hayden, Fish and Game Department regional wildlife manager.

Biologists found 35 pairs of nesting opsrey in a North Idaho survey area in 1986. The same area held 56 pairs last year, even though some ospreys have been captured in the Panhandle for relocation in Colorado.

The banning of DDT in the United States in 1972 helped the birds, said Hoffman, who founded HawkWatch in Albuquerque 10 years ago and moved the organization’s headquarters to Salt Lake City in 1992.

“You would not expect a species of raptor that lays a few eggs and lives a long time to be increasing at this fast a rate,” he said.

“It indicates the populations were very suppressed as a result of pesticides and now they’re just exploding,” Hoffman said. “The big question is when are they going to level off? They can’t grow forever.”

Because DDT does not break down readily in the environment, several years were required for bird populations to begin recovering.

DDT disrupts calcium metabolism in female birds and consequently causes them to lay eggs with unusually thin shells that are easily crushed when adult birds sit on them during nesting.

Merlins and peregrines have absorbed particularly high concentrations of DDT because they only eat other birds and so are near the top of the food chain.

“The banning of DDT was of course very important,” said Steve Spangle, an endangered species biologist with the U.S. Fish and Wildlife Service.

“I think there’s a better awareness now about the importance of raptors, whereas they were more likely to be shot in the old days,” he said.

HawkWatch researchers have gathered 18 years worth of data from single sites in Nevada and Utah and two sites in New Mexico.

The average annual population increase for up to 18 years were 12.1 percent for peregrines, 14.6 percent for merlins and 8.9 percent for ospreys, Hoffman said.

Spangle said peregrines have been helped by captive breeding programs and reintroduction efforts.

At least one pair of peregrine falcons re-introduced to North Idaho has established an aerie in the Panhandle near Sandpoint, Hayden said.

Hoffman said ospreys might have benefitted from the West’s dams and the fish in the reservoirs behind them.

Ospreys also have been helped by the efforts of conservation groups to restore the birds’ habitat, he said.

Turkey vultures, which feed on carrion, are not raptors, but they were included in the survey anyway.

They have increased, too, but probably for much different reasons.

More roads and more traffic has increased the number of wild creatures struck by vehicles, Hoffman said, noting that road kills are a boon to turkey vultures.

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