Bald eagles (Haliaeetus leucocephalus) are considered a recovery success in the United States after rebounding from near extirpation due to widespread use of the insecticide dichlorodiphenyltrichloroethane (DDT) in the twentieth century. Although abundances of bald eagles have increased since DDT was banned, other contaminants have remained in the environment with unknown influence on eagle population trends. Ingestion of spent lead (Pb) ammunition, the source of Pb most available to eagles and other scavengers in the United States, is known to kill individual eagles, but the influence of the contaminant on overall population dynamics remains unclear, resulting in longstanding controversy over the continued legality of the use of Pb in terrestrial hunting ammunition. We hypothesized that mortalities from the ingestion of Pb reduced the long‐term growth rate and resiliency of bald eagles in the northeast United States over the last 3 decades. We used Holling's definition of resilience (the ability of a system to absorb changes of state variables, driving variables, and parameters and still persist) to quantify how reduction in survival from Pb‐associated mortalities reduced the likelihood of population persistence. We used a population matrix model and necropsy records gathered between 1990 and 2018 from a 7‐state area to compare population dynamics under current versus hypothetical Pb‐reduced and Pb‐free scenarios. Despite a robust increase in eagle abundances in the northeast United States over that period, we estimated that deaths arising from ingestion of Pb was associated with a 4.2% (females) and 6.3% (males) reduction in the asymptotic long‐term growth rate (lambda). Comparison between real (current) and counterfactual (Pb‐reduced and Pb‐free) population dynamics indicated that the deaths from acute Pb poisoning were additive because the mortality events were associated with marked reduction in annual survival performance of hatchlings and reproductive females. These shifts in survival performance were further associated with a reduction in resilience for hatchling (95.4%) and breeding (81.6%) female eagles. Counterintuitively, the current conditions produced an increase in resilience (68.9%) for immature and non‐breeding female eagles over hypothetical Pb‐free conditions, suggesting that the population of eagles in the northeast United States reorganized (in a population dynamics sense) to ensure population expansion despite additive mortalities associated with Pb. This study can be used by state and federal wildlife managers or non‐governmental organizations to inform policy surrounding the use of lead ammunition or to educate hunters on the population‐scale effects of their ammunition choices.
ABSTRACT:Capture-related injuries or deaths of wildlife study subjects pose concerns to researchers, from considerations for animal welfare to inflated project costs and biased data. Capture myopathy (CM) is an injury that can affect an animal's survival #30 days postrelease, but is often difficult to detect without close monitoring and immediate necropsy. We evaluated the influence of capture and handling on postcapture movement in an attempt to characterize movement rates of animals suffering from CM. We captured and global positioning systemcollared 95 white-tailed deer (Odocoileus virginianus) in central and northern New York during 2006-2008. Six juveniles died within 30 days postrelease, and necropsy reports indicated that two suffered CM (2%). We compared postcapture movement rates for juveniles that survived .30 days with those that died #30 days postcapture. Survivor movement rates (43.74 m/hr, SD53.53, n528) were significantly higher than rates for deer that died within 30 days (17.70 m/hr, SD51.57, n56) (P,0.01). Additionally, movement rates of juveniles that died of CM (15.1 m/hr) were 5.1 m/hr lower than those for juveniles that died of other causes #30 days postcapture (20.2 m/hr), but we were unable to evaluate this statistically because of insufficient sample size. We found no difference in vital rates (temperature, heart rate, respiration rate) during handling between survivors and juveniles that died within 30 days postcapture but observed that survivors were in better body condition at capture. These results suggest that deer likely to die within the 30-day CM window can be identified soon after capture, provided that intensive movement data are collected. Further, even if necropsy reports are unavailable, these animals should be censored from analysis because their behavior is not representative of movements of surviving animals.
Anticoagulant rodenticides (AR), principally difethialone, brodifacoum, and bromadiolone, were detected in the livers of 89% of 72 red-tailed hawks ( Buteo jamaicensis) from New York City, New York, USA examined for cause of death over a 7-yr period (January 2012–December 2018). Fatal hemorrhage likely attributable to AR exposure was diagnosed in 41% (30/74) of cases, and 46% (18/39) of the cases analyzed with no gross evidence of AR-mediated hemorrhage had liver concentrations of AR that overlapped those with an AR-poisoning diagnosis. Although urban areas like New York City can support surprisingly dense populations of red-tailed hawks, the threat posed by extensive use of AR can be large.
While the recent population recovery of bald eagles (Haliaeetus leucocephalus) in New York State, USA, is a conservation success, evidence from necropsies suggest that ingested lead (Pb) from ammunition fragments is causing morbidity and mortality to wild eagles. Wildlife managers and officials at the New York State Department of Environmental Conservation would benefit from analysis of their necropsy data to understand how documented morbidities or mortalities impact dynamics of the remaining wild eagle population. We integrated necropsy data on bald eagles in New York State collected between 1990 and 2018 by the New York State Department of Environmental Conservation into a matrix population model. We compared annual survival of hatchling, non-breeding, and breeding eagles under factual (Pb) and counter factual (Pb-reduced or Pb-free) scenarios. We found no evidence that Pb altered annual survival of hatchlings. Lead was associated with a reduction in the annual survival of nonbreeders by 0-0.056 (females) and 0.052-0.057 (males), and a reduction in the annual survival of breeders by 0.051-0.057 (females) and 0-0.032 (males). Lead was associated with a reduction in the long-term growth rate (λ) by 0.009-0.036 (females) and 0.023-0.035 (males). Due to altered dynamics over the prior 3 decades, abundances of eagles in the most recent year of the study (2018) differed between Pb
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