U.S. Fish and Wildlife Service Bald and Golden Eagles – 2016 Status Report Eagles Golden and Bald Bald and Golden Eagles Population Demographics and Estimation of Sustainable Take in the United States, 2016 update ii Bald and Golden Eagles Population demographics and estimation of sustainable take in the United States, 2016 update April 26, 2016 Authors Brian A. Millsap, Emily R. Bjerre, Mark C. Otto, Guthrie S. Zimmerman, and Nathan L. Zimpfer U.S. Fish and Wildlife Service Division of Migratory Bird Management Disclaimer: The information in this report is intended to aid in the development of regulations and inform eagle management decisions by the U.S. Fish and Wildlife Service. The recommendations and findings in the report do not constitute U.S. Fish and Wildlife Service policy, but they will be considered by the U.S. Fish and Wildlife Service as it sets eagle management policies. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Suggested Citation: U.S. Fish and Wildlife Service. 2016. Bald and Golden Eagles: Population demographics and estimation of sustainable take in the United States, 2016 update. Division of Migratory Bird Management, Washington D.C., USA. iii Acknowledgments We gratefully acknowledge contributions of data from tagged golden eagles by Bryan Bedrosian, Pete Bloom, James Cain, Ross Crandall, Robert Domenech, Daniel Driscoll, Jamey Driscoll, Mark Fuller, Rick Gerhardt, Al Harmata, Todd Katzner, Robert Knight, Craig Koppie, Brian Latta, Mike Lockhart, Mark Martell, Carol McIntyre, Libby Mojica, Robert Murphy, Gary Roemer, Steve Slater, Jeff Smith, Dale Stahlecker, Brian Washburn, and Jim Watson. Andrew Dennhardt provided additional information on eastern U.S. golden eagle population estimates. Bruce Peterjohn and Danny Bystrak with the U.S. Geologic al Survey Bird Banding Lab helpfully provided banding data. The analyses and report greatly benefited from reviews and assistance provided by members of the Service’s Eagle Technical Assessment Team, and we are especially grateful for a thorough review by Todd Katzner. Analyses of the bald eagle post-delisting survey data were improved by input from John Sauer and William Link, and population models and harvest analyses were improved by suggestions and input from Michael Runge, John Sauer, and Leslie New. Gabriela Chavarria (U.S. Fish and Wildlife Service, Science Applications) was instrumental in funding a significant portion of the on-going PTT-tagging study for golden eagles. We appreciated comments on an earlier draft by Leon Kolankiewicz, and Eliza Savage. Any errors or omissions are the responsibility of the senior author. iv Executive Summary In June 2014 the U.S. Fish and Wildlife Service (Service) announced its intent to consider several revisions to regulations at 50 CFR, part 22 that pertain to permits to take bald (Haliaeetus leucocephalus) and golden (Aquila chrysaetos) eagles. The Service is preparing a Programmatic Environmental Impact Statement (PEIS) to evaluate the potential effects of the revised regulations on eagle population status. The PEIS will analyze alternatives that include both conservative and liberal take rates for both species, consistent with the overall management objective of maintaining stable or increasing populations relative to estimated population levels in 2009. The liberal alternatives will use take rates estimated from the median values for relevant parameters (e.g., population size, growth rates), and the conservative alternatives will use the 20th quantile values of parameter estimates. The alternatives will also consider different configurations of eagle management units (EMUs): (1) the current EMUs, which are Bird Conservation Regions (BCRs) for golden eagles, and approximately Service regional boundaries for bald eagles based on nest densities; and (2) the four administrative migratory bird flyways (i.e., Atlantic, Mississippi, Central, and Pacific). To inform the evaluation of the PEIS alternatives, a subgroup of the Service’s Eagle Technical Assessment Team compiled recent information on population size and trend of both species of eagle, generated estimates of recent survival and fecundity rates, and used these data in models to predict future population trends and the ability of each species to withstand additional mortality in the form of permitted take. This document summarizes the findings from those analyses. The team (hereafter we) estimated population size for the bald eagle in the coterminous United States (U.S.) using a population model in conjunction with estimates of the number of occupied nesting territories (representing the number of breeding pairs) in 2009 from a comprehensive dual-frame aerial survey. That population size estimate combined with a previous estimate of population size for Alaska was 143,000 (20th quantile = 126,000) bald eagles for the entire U.S. in 2009. This represents an increase in population size since 2007 in the coterminous U.S. (the year the final rule for delisting under the Endangered Species Act was published). We attribute the difference to improved survey and estimation efforts, as well as increases in bald eagle numbers. Consistent with the population model, independent Breeding Bird Survey (BBS) indices indicated bald eagles are continuing to increase over much of the U.S. We used a potential biological removal model to estimate sustainable take rates and limits with the goal of maintaining at least the 2009 population level, and concluded that under the liberal alternative bald eagles over most of the country can support an annual take rate of 8% (20th quantile = 6% under the conservative alternative). The exceptions are the Southwestern U.S., where population growth potential is lower, and Alaska, where limited survey information led managers to select a lower management objective factor; there, the sustainable take rates are 4.5% (20th quantile = 3.8%) and less than 1%, respectively. Nationally, the annual bald eagle take limit with these rates would be approximately 6,300 eagles under the liberal alternative and 4,200 eagles under the conservative alternative. We estimated population size for the golden eagle by first estimating a population size for the western coterminous U.S. using a composite model that integrated multi-year information from a late summer aerial transect survey over the interior western U.S. with information from the BBS. Population size for Alaska could not be estimated directly. Instead, we used results from mid-winter aerial transect surveys in 2014 and 2015 over the same area as the interior western U.S. summer transect survey to estimate the increase in population size between late summer and winter. The increase was used as a coarse estimate of the size of the overwintering migrant population. We allocated 24% of the winter increase to Alaska as a conservative population estimate, assuming migrants originated proportionately across western Canada and v Alaska. A population size estimate for eastern North America was available from the literature. Combining the western coterminous U.S., Alaska, and eastern U.S. estimates, total population size for the golden eagle in the U.S. (including Alaska) was approximately 39,000 (20th quantile = 34,000) in 2009 and 40,000 (20th quantile = 34,000) in 2014. The population trend estimate from the composite model was stable, but an estimate from a population model similar to that used for the bald eagle suggested the population in the coterminous western U.S. might be declining towards a lower equilibrium size. Thus, taking into account the uncertainty, the available data for golden eagles are somewhat equivocal, with count data suggesting a stable population but with demographic data forecasting a slight decline. We used banding data obtained from the United States Geological Survey Bird Banding Lab from 1968–2014 to estimate contemporary age-specific survival rates. We also used a data set of unbiased cause-of­ mortality information for a sample of 386 satellite-tagged golden eagles from 1997–2013 to estimate the effect of current levels of anthropogenic mortality on those survival rates. Anthropogenic factors were responsible for about 56% of satellite-tagged golden eagle mortality, but rates of anthropogenic mortality varied among age-classes, ranging from 34% for first-year eagles to 63% for adults. We estimated the maximum rate of population growth for the golden eagle in the U.S. in the absence of existing anthropogenic mortality was 10.9% (20th quantile = 9.7%). Sustainable take under these conditions is close to 2,000 individuals (20th quantile = 1,600). However, available information suggests ongoing levels of human-caused mortality likely exceed this value, perhaps considerably. Thus, the data from satellite tags lends further support to the suggestion from the demographic models that current survival rates may be leading to a decline in population size. The Service also has a need to apply take values to nest disturbance and loss. We updated metrics for converting take via nest disturbance and nesting territory loss to debits from the EMU take limits for bald and golden eagles. The current policy is that for each instance of authorized take through disturbance in each year the nest is disturbed, the Service reduces EMU take limits by the median number of young that would have been expected to fledge from the disturbed territory. The updated median productivity values are 1.12 for the bald eagle (0.73 in the Southwest region only), and 0.54 for the golden eagle. By carrying forward the above debits from the EMU take limits for a period of years equal to the species or population-specific generation time (10 years for the bald eagle—12 years in the Southwest, and 11 years for the golden eagle), we also calculated a take value for nesting territory loss (i.e., the territory becomes permanently vacant). In addition to setting EMU take limits, the Service has established local-area population (LAP) thresholds for permitted take when authorized take in a local area might have long-term negative consequences at that scale.