TRI-CITIES-- Ten ferruginous hawks in southcentral Washington are wearing satellite telemetry transmitters so that Washington Department of Fish and Wildlife (WDFW) biologists can learn more about the threatened species to help recover their declining population.
The birds, nine adults and one juvenile, were captured and equipped this summer in their nesting territories near the Tri-Cities in Benton and Franklin counties. The transmitters send signals to satellites which relay location information back to ground stations. From there WDFW biologists retrieve the information via computer daily, within two to six hours of signal reception, to track the hawks' movements.
The need to follow the birds so closely comes in part from their apparent tendency to roam widely without patterns of foraging and nesting, at least in recent years in Washington state. These irregularities and the species population decline may be due to fluctuations in available prey, such as jackrabbits and ground squirrels. Tracking their movements more precisely will help determine habitat use and needs for securing habitat to recover the species.
Ferruginous hawks also migrate long distances, says WDFW wildlife research scientist Jim Watson, who is heading up the study. Washington's ferruginous hawks probably winter in the western states, and as far south as Mexico, but nothing is actually known of their regional or long-range movements.
"We need to know if they get ‘bottlenecked' in wintering areas because of habitat limitations or pesticide use "so we can better understand our local population decline," Watson explained. "The satellite transmitters will provide year-round, ‘unlimited mileage' tracking."
The two-year study, in cooperation with Battelle Pacific Northwest National Laboratories, also is an opportunity to educate people about ferruginous hawks, said Watson. Funding support comes from Seattle's Woodland Park Zoo and the Grand Coulee School District, whose respective visitors and students eventually will be following the progress of the hawks through planned Internet access to relocation data.
The ferruginous hawk is North America's largest "buteo" or broad-winged hawk, over two feet long with a 4-to 5- foot wingspan. Adults have reddish-brown upper bodies and flanks ("ferruginous" means having the color of iron rust) and whitish under parts. They prey mostly on small-to-medium-sized mammals in open habitats such as eastern Washington's grasslands and shrub-steppe. They arrive here in February or March to nest atop isolated trees or rock outcroppings with unobstructed views. Young hatch in April or May and fledge (first fly) in June or July. By September they disperse from nesting areas.
WDFW estimates that 50 to 60 pairs of ferruginous hawks now nest in Washington. Vacant nests indicate that historically at least 222 pairs may have nested here. The species was listed as "threatened" in 1983 by the state. Nationwide populations may be stable or in slow decline, with estimates of 5,000 to 6,000 pairs. The U.S. Fish and Wildlife Service considers the bird a "species of concern."
Declines in prey populations, such as blacktail jackrabbits, may be part of the problem. Conversion of native plants through cultivation and livestock grazing may have reduced those prey populations. Other land use changes and human pressures may be factors, too.