A year ago, biologist Stephen W. Hoffman said he felt three raptor species might be declining. Tuesday he had the figures to back up his hunch about two of them.
Hoffman, president of the non-profit HawkWatch International Inc., based in Albuquerque, said in December 1990 that the group suspected problems with golden eagles, northern goshawks and prairie falcons.HawkWatch volunteers count raptors in the fall at four sites - in the Wellsville Mountains of northern Utah; the Goshute Mountains near the Utah-Nevada border; Sandias, N.M.; and Manzanos, N.M. They also band and release birds.
Downward trends for golden eagles and northern goshawks were noted at three of the four sites that the group staffs in the West; the exception is the trend at the Goshute Mountains.
Raptor populations usually fluctuate with the availability of prey - in this case, usually jackrabbits. In areas where jackrabbits are abundant, the birds stay around, but they'll migrate away from regions of rabbit scarcity.
In addition, rabbit populations naturally follow a 10-year cycle of boom and bust, Hoffman said. So to understand the changes in the populations of hawks and eagles, it's necessary to count them over more than 10 years so that a whole cycle can be observed.
With the Wellsville Mountains site set up in 1977, HawkWatch now has data from two different cycles.
Comparing the time just before the peaks of the two 10-year cycles, he said, shows both golden eagles and northern goshawks decreasing as much as 50 percent.
During a press conference Tuesday at Tracy Aviary in Liberty Park, Hoffman said the two species "may be on the downslide."
In talks with experts, he said, he's determined the possible cause could involve the destruction of native perennial grasses on the range, and replacement with exotic species like cheatgrass. Many areas are burned by brush fires.
The gradual diminution of the grass means that an area will support fewer rabbits, resulting in reductions of raptors that depend on the rodents.
"This means more than the loss of the golden eagle," he said. The golden eagle is the predator at the top of the food chain; if it's declining, the indication is that the entire ecosystem is in trouble.
Destruction of the grasses also harms livestock ranchers, because cattle and sheep depend on the perennials, Hoffman said.
Asked what could cause the change in grasses, he said, "I think a combination of intensive, long-term, heavy grazing by livestock, combined with periodic droughts, has been very, very tough on the perennial grasses." In addition, exotic species are moving in and damaging the perennials.
Other possible causes of the decline are contamination with heavy metal pollution, lead poisoning from shotgun pellets in prey, and pesticides, he said. Although pesticides don't target hawks and eagles, they can build up in the food chain.
Hoffman called for further research to see if the downward trend continues. He said he wants to raise a red flag of warning because it's much easier to save a species before it becomes terribly endangered.
(Additional information)
Program lets you 'Adopt-A-Hawk'
Stephen W. Hoffman, president of HawkWatch International, appeared at a press conference Tuesday with Redford, the red-tailed hawk, for two reasons: to alert the public to a possible decline in golden eagles and northern goshawks and to publicize his group's "Adopt-A-Hawk" program.
People donating money to the conservation of the hawks and eagles can choose the type of bird of prey to "adopt," at prices ranging from $25 to $300, depending on rarity. The sponsor gets an adoption certificate with the bird's species, weight, sex, age, band number and a color photo.
The birds aren't actually brought into an adopter's home, of course. They are banded and released. But the adopter gets periodic updates on the bird's activities, when known, and also information about the species.
The conservation group gets about one-third of its operating expenses through the Adopt-A-Hawk program.
For more information, Hoffman will give a slide show and lecture from 7:30 p.m. to 9:30 p.m. Wednesday, at the First Baptist Church, 777 S. 1300 East; or telephone toll-free, 1 (800) 726-4295.