Threatened and Endangered Species - Status Reports
Date Published: February 2002
Number of Pages: 87
Author(s): Gerald E. Hayes and Joseph B. Buchanan
The peregrine falcon (Falco peregrinus) experienced a dramatic population decline over much of its nearly global range following the widespread use of the insecticide DDT shortly after World War II. Peregrines are aerial hunters of birds and their tissue accumulated DDT and other organochlorine pesticides from their prey. This contaminant load caused eggshell thinning and other toxic effects. The thinned eggshells broke on nest ledges or eggs were not viable, and this facilitated a rapid population decline that extirpated the species from eastern North America and greatly reduced its abundance in western North America. The peregrine was listed as an endangered species by the U.S. Fish and Wildlife Service in 1970 and by the Washington State Fish and Wildlife Commission in 1980. An endangered species is defined in Washington Administrative Code as a species native to the state ".. that is seriously threatened with extinction throughout all or a significant portion of its range within the state" (WAC 232-12-297). DDT use in North America ceased in the early 1970s. At about that same time efforts to breed peregrines in captivity were proving successful and beginning in the 1980s and extending through much of the 1990s progeny of captive-bred falcons were released annually at various locations in the Columbia Gorge, Cascade Mountains and eastern Washington via "hacking." Hacking efforts proved to be successful in providing recruits to Washington’s breeding population.
The banning of DDT, along with peregrine reintroduction programs, and the protection of nest sites, allowed the population to increase over the last 20 year period. Prior to 1980, 12 traditional breeding sites were known, although historical accounts may have greatly underestimated population size. WDFW began monitoring the population in the late 1970s and found only 5 pairs in the state by 1980. The population has increased substantially since that time and in 2001 there were 72 pairs and 89 known territories. Over the last five year period productivity has averaged 1.53 young per territorial pair, a rate associated with a stable population, and new sites continue to be found annually. The peregrine falcon now breeds in most portions of the state where there are prominent cliffs for nesting and an abundance of prey. Eggshell-thinning has averaged 11.4 -12.6% over the last two decades and remains below critical thresholds (15-20%) associated with reproductive impairment at the population level.
Although Washington’s peregrine population is small, given the dramatic increase in number and distribution in the last 20 years, WDFW believes a change in the species status is warranted. Peregrines still exhibit eggshellthinning compared to pre-DDT values, but the thinning level is below critical threshold values and appears to have stabilized. In addition, the population continues to increase in the state, occupancy remains high at known sites and productivity appears consistent with healthy populations. Peregrines are now well distributed in Washington, and their way of life as a solitary predator limits the impact that most threats would have to a more social animal. Environmental contamination is one of the few threats that can impact such a sparsely dispersed species. For these reasons we do not believe the species is likely to become endangered within the foreseeable future and therefore do not recommend a down-listing to threatened status.
Washington’s peregrine population remains vulnerable due to its small numbers (72 occupied territories in 2001). WDFW and cooperators continue to monitor the known sites; and WDFW interacts with various landowners and agencies on disturbance and other issues that could jeopardize nest site occupancy at individual sites. DDT impacted peregrine populations across the species’ broad geographic range. Because of the widespread presence of various industrial and agricultural chemicals in the environment, accumulations of harmful pollutants may pose a threat to the ongoing recovery of Washington’s population. Although eggshell thickness values have not returned to levels considered normal in the pre-DDT era, this does not appear to impair the growth of Washington’s population. However, the small population warrants continued monitoring and management of potential disturbance at nest sites on an individual basis.
For these reasons WDFW believes the peregrine should be down-listed but requires continued cooperative management. WDFW believes the appropriate status for the peregrine is sensitive. A state sensitive species is considered "a species native to the state of Washington that is vulnerable or declining and is likely to become endangered or threatened in a significant portion of its range within the state without cooperative management or removal of threats" (WAC 232-12-297).
Hayes, G. E. and J. B. Buchanan. 2002. Washington State status report for the Peregrine Falcon. Washington Dept. Fish and Wildlife, Olympia. 77 pp.
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