Age‐specific survival rates, causes of death, and allowable take of golden eagles in the western United States

Abstract

In the United States, the Bald and Golden Eagle Protection Act prohibits take of golden eagles (Aquila chrysaetos) unless authorized by permit, and stipulates that all permitted take must be sustainable. Golden eagles are unintentionally killed in conjunction with many lawful activities (e.g., electrocution on power poles, collision with wind turbines). Managers who issue permits for incidental take of golden eagles must determine allowable take levels and manage permitted take accordingly. To aid managers in making these decisions in the western United States, we used an integrated population model to obtain estimates of golden eagle vital rates and population size, and then used those estimates in a prescribed take level (PTL) model to estimate the allowable take level. Estimated mean annual survival rates for golden eagles ranged from 0.70 (95% credible interval = 0.66–0.74) for first‐year birds to 0.90 (0.88–0.91) for adults. Models suggested a high proportion of adult female golden eagles attempted to breed and breeding pairs fledged a mean of 0.53 (0.39–0.72) young annually. Population size in the coterminous western United States has averaged ~31,800 individuals for several decades, with λ = 1.0 (0.96–1.05). The PTL model estimated a median allowable take limit of ~2227 (708–4182) individuals annually given a management objective of maintaining a stable population. We estimate that take averaged 2572 out of 4373 (59%) deaths annually, based on a representative sample of transmitter‐tagged golden eagles. For the subset of golden eagles that were recovered and a cause of death determined, anthropogenic mortality accounted for an average of 74% of deaths after their first year; leading forms of take over all age classes were shooting (~670 per year), collisions (~611), electrocutions (~506), and poisoning (~427). Although observed take overlapped the credible interval of our allowable take estimate and the population overall has been stable, our findings indicate that additional take, unless mitigated for, may not be sustainable. Our analysis demonstrates the utility of the joint application of integrated population and prescribed take level models to management of incidental take of a protected species.

Method to assess the potential magnitude of terrestrial European avian population reductions from ingestion of lead ammunition

“…The results indicate greater numeric losses when populations are growing (i.e., higher losses resulted using 2013–2018 short term period trends that had more increasing populations) or when a species has higher reproductive rates (gallinaceous birds vs. raptors). The number of birds lost and even the percentage reduction in the population size when a population is growing might be of interest [9, 10 and used in ECHA [ 1 ] but is not as crucial as understanding change in population sustainability [ 13 ]. A management goal for vulnerable species is to have increasing and sustainable avian populations.…”

“…Our upper bound is solely based on metrics of tissue concentrations or observed lead shot in the gizzard (not diagnoses), and likely overestimates loss because it uses a very low threshold for mortality occurring that is actually considered subclinical, and lead concentrations at clinical or even severely clinical concentrations are not definitive indicators of death [ 15 , 32 ], particularly for gallinaceous birds [ 2 ]; a necropsy diagnosis may be more informative [ 33 ]. We believe this novel approach of bounding the uncertain range in this manner may be superior than assuming exceedance of a clinical or severe clinical tissue threshold results in death as done in other studies [ 11 , 12 , 15 ] or assuming only direct deaths are caused by lead poisoning [ 13 ].…”

“…In addition to lead shot, toxicity from lead bullet or slug fragments in prey or hunter-discarded offal consumed by raptors is of particular concern [ 11 , 12 ]. Recently, researchers have evaluated effects of lead ammunition ingestion on eagle populations in the United States of America (USA) using tissue concentrations in carcasses combined with population modeling, but those methods either required relatively complete records of number of all bird deaths by lead poisoning in the study area (eastern USA [ 11 ]) or extensive banding and transmitter tracking data (western USA [ 13 ]). Because of this lack of information across countries in Europe, ECHA [ 1 ] was unable to develop a quantitative or qualitative estimate of the percentage of terrestrial European carnivorous birds with lead poisoning, and they developed only a highly uncertain estimate of 1% decrease in terrestrial game birds from lead shot ingestion.…”

Selecting auditory alerting stimuli for eagles on the basis of auditory evoked potentials

“…American kestrels (3.1%) and red-tailed hawks (2.9%) make up the majority of the diurnal raptor mortalities, but these species also have large population sizes and are widespread across the USA. Golden eagles account for only a handful of raptor mortalities, but have relatively small population sizes ( U. S. Fish and Wildlife Service, 2016 ; Millsap et al , 2022 ), and are therefore a high conservation priority around wind energy facilities built in potential eagle habitat.…”

Golden eagle use of winter roadkill and response to vehicles in the western United States

“…The rates at which eagles are struck in association with feeding on roadkill are difficult to determine because of a lack of standardized reporting and generally short eagle carcass persistence times related to collection for feathers, both legally (i.e., for the National Repository) and illegally (i.e., black market; Katzner et al 2020). Human-caused mortality of golden eagles currently exceeds sustainable take levels in North America (USFWS 2016, Katzner, et al 2020, Millsap et al 2022). As a result, any federally permitted mortality associated with human development (e.g., wind turbines) must be offset by mortality reductions or increased productivity elsewhere (USFWS 2016).…”