Glen Canyon National Recreation Area Eagle Survey Report: Winter 1996-1997

Brown, Nikolle

The Bald Eagle (Haliaeetus leucocephalus) is a migratory species that can be found wintering in Glen Canyon National Recreation Area (NRA). Historically, their distribution was nationwide; however, populations of bald eagles outside of Alaska have declined because of habitat loss and reproductive failure due to pesticides and heavy metals in their diets. In combination with the protection of this species through the Bald Eagle Act of 1940 and federal listing as Endangered under the Endangered Species Act of 1973, recent restrictions placed on certain pesticides have allowed for the comeback of this species in some of its historic range. Because of the overall increase in the numbers, which have met the recovery goals set by the U. S. Fish and Wildlife Service (USFWS), the bald eagle was reclassified from endangered to threatened in 1995. Threatened species are defined as any species that is likely to become an endangered species within the foreseeable future throughout all or a significant part of its range (USFWS 1995). Industrial development, logging, recreational development, and other human disturbances have caused eagles to abandon nests and remain potential threats of this species. Wintering bald eagles are opportunistic feeders and will concentrate in areas where prey availability is high and energy expenditure to capture prey is low (Stahlmaster 1987). High numbers of migratory waterfowl around and the abundance of fish in Lake Powell and the Colorado River in the winter months make for ideal winter foraging grounds for bald eagles. Winter surveys for bald eagles around Glen Canyon NRA have been conducted since 1983. These surveys usually consisted of one-day aerial surveys or boat surveys conducted monthly from November through March. In 1990-91, the aerial surveys were conducted bi-weekly and initiated the inclusion of golden eagles (Aquila chrysaetos) into the survey efforts. In 1991-92, boat surveys were conducted in addition to the monthly aerial surveys. Due to budget constraints and the less concern for the species, only two aerial surveys were conducted in the winter 1996-97 on 10 January 1997 and 3 February 1997. Of these, the January survey was conducted as a part of Arizona Game and Fish’s state-wide bald eagle survey.