title: Quantifying the demographic cost of human-related mortality to a raptor population.
abstract: Raptors are exposed to a wide variety of human-related mortality agents, and yet population-level effects are rarely quantified. Doing so requires modeling vital rates in the context of species life-history, behavior, and population dynamics theory. In this paper, we explore the details of such an analysis by focusing on the demography of a resident, tree-nesting population of golden eagles (Aquila chrysaetos) in the vicinity of an extensive (142 km2) windfarm in California. During 1994-2000, we tracked the fates of >250 radio-marked individuals of four life-stages and conducted five annual surveys of territory occupancy and reproduction. Collisions with wind turbines accounted for 41% of 88 uncensored fatalities, most of which were subadults and nonbreeding adults (floaters). A consistent overall male preponderance in the population meant that females were the limiting sex in this territorial, monogamous species. Estimates of potential population growth rate and associated variance indicated a stable breeding population, but one for which any further decrease in vital rates would require immigrant floaters to fill territory vacancies. Occupancy surveys 5 and 13 years later (2005 and 2013) showed that the nesting population remained intact, and no upward trend was apparent in the proportion of subadult eagles as pair members, a condition that would have suggested a deficit of adult replacements. However, the number of golden eagle pairs required to support windfarm mortality was large. We estimated that the entire annual reproductive output of 216-255 breeding pairs would have been necessary to support published estimates of 55-65 turbine blade-strike fatalities per year. Although the vital rates forming the basis for these calculations may have changed since the data were collected, our approach should be useful for gaining a clearer understanding of how anthropogenic mortality affects the health of raptor populations, particularly those species with delayed maturity and naturally low reproductive rates.
authors.affiliation: The Peregrine Fund, Boise, Idaho, United States of America.|Predatory Bird Research Group, Long Marine Laboratory, University of California, Santa Cruz, California, United States of America.
authors.forename: W
authors.initials: W
authors.lastname: Grainger Hunt
authors.affiliation: United States Geological Survey, Forest and Rangeland Ecosystem Science Center, Corvallis, Oregon, United States of America.
authors.forename: J
authors.initials: J
authors.lastname: David Wiens
authors.affiliation: Centre for African Conservation Ecology, Nelson Mandela Metropolitan University, Port Elizabeth, Republic of South Africa.
authors.forename: Peter R
authors.initials: PR
authors.lastname: Law
authors.affiliation: United States Geological Survey, Forest and Rangeland Ecosystem Science Center, Boise, Idaho, United States of America.
authors.forename: Mark R
authors.initials: MR
authors.lastname: Fuller
authors.affiliation: Predatory Bird Research Group, Long Marine Laboratory, University of California, Santa Cruz, California, United States of America.|Garcia and Associates, San Anselmo, California, United States of America.
authors.forename: Teresa L
authors.initials: TL
authors.lastname: Hunt
authors.affiliation: Predatory Bird Research Group, Long Marine Laboratory, University of California, Santa Cruz, California, United States of America.|American Eagle Research Institute, Apache Junction, Arizona, United States of America.
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Driscoll
authors.affiliation: Predatory Bird Research Group, Long Marine Laboratory, University of California, Santa Cruz, California, United States of America.|Garcia and Associates, San Anselmo, California, United States of America.
authors.forename: Ronald E
authors.initials: RE
authors.lastname: Jackman
mesh_terms: D000465:Algorithms; D000818:Animals; D002140:California; D003247:Conservation of Natural Resources; D005260:Female; D005298:Fertility; D005843:Geography; D006801:Humans; D008297:Male; D015233:Models, Statistical; D011157:Population Dynamics; D011158:Population Growth; D020304:Raptors; D012621:Seasons; D013731:Territoriality; D013997:Time Factors; D014919:Wind