Geology topics

Jeremy A. Buck

Publications and source records attributed to Jeremy A. Buck.

5 recordsLinked to original sources

USGS2023

Anticoagulant rodenticides are associated with increased stress and reduced body condition of avian scavengers in the Pacific Northwest

Anticoagulant rodenticides (AR) have been used globally to manage commensal rodents for decades. However their application has also resulted in primary, secondary, and tertiary poisoning in wildlife. Widespread exposure to ARs (primarily second generation ARs; SGARs) in raptors and avian scavengers has triggered considerable conservation concern over their potential effects on populations. To identify risk to extant raptor and avian scavenger populations in Oregon and potential future risk to the California condor ( Gymnogyps californianus ) flock recently established in northern California, we assessed AR exposure and physiological responses in two avian scavenger species (common ravens [ Corvus corax ] and turkey vultures [ Cathartes aura ]) throughout Oregon between 2013 and 2019. AR exposure was widespread with 51% (35/68) of common ravens and 86% (63/73) of turkey vultures containing AR residues. The more acutely toxic SGAR brodifacoum was present in 83% and 90% of AR exposed common ravens and turkey vultures. The odds of AR exposure in common ravens were 4.7-fold higher along the coastal region compared to interior Oregon. For common ravens and turkey vultures that were exposed to ARs, respectively, 54% and 56% had concentrations that exceeded the 5% probability of toxicosis (>20 ng/g ww; Thomas et al., 2011), and 20% and 5% exceeded the 20% probability of toxicosis (>80 ng/g ww; Thomas et al., 2011). Common ravens exhibited a physiological response to AR exposure with fecal corticosterone metabolites increasing with sum ARs (ΣAR) concentrations. Both female common raven and turkey vultures’ body condition was negatively correlated with increasing ΣAR concentrations. Our results suggest avian scavengers in Oregon are experiencing extensive AR exposure and the newly established population of California condors in northern California may experience similar AR exposure if they feed in southern Oregon. Understanding the sources of ARs across the landscape is an important first step in reducing or eliminating AR exposure in avian scavengers.

Oregon↗

USGS2021

Small mammal shooting as a conduit for lead exposure in avian scavengers

Lead (Pb) exposure is a widespread wildlife conservation threat. Although commonly associated with Pb-based ammunition from big-game hunting, small mammals (e.g., ground squirrels) shot for recreational or pest-management purposes represent a potentially important Pb vector in agricultural regions. We measured the responses of avian scavengers to pest-shooting events and examined their Pb exposure through consumption of shot mammals. There were 3.4-fold more avian scavengers at shooting fields relative to those at fields with no recent shooting, and avian scavengers spent 1.8-fold more time feeding after recent shooting events. We isotopically labeled shot ground squirrels in the field with an enriched 15N isotope tracer; 6% of avian scavengers sampled within a 39 km radius reflected this tracer in their blood. However, 33% of the avian scavengers within the average foraging dispersal distance of nests (0.6−3.7 km) were labeled, demonstrating the importance of these shooting fields as a source of food for birds nesting in close proximity. Additionally, Pb concentrations in 48% of avian scavengers exceeded subclinical poisoning benchmarks for sensitive species (0.03−0.20 μg/g w/w), and those birds exhibited reduced δ-aminolevulinic acid dehydratase activity, indicating a biochemical effect of Pb. The use of shooting to manage small mammal pests is a common practice globally. Efforts that can reduce the use of Pb-based ammunition may lessen the negative physiological effects of Pb exposure on avian scavengers.

Oregon↗

USGS2020

The lead (Pb) lining of agriculture‐related subsidies: enhanced Golden Eagle growth rates tempered by Pb exposure

Supplementary food resources (e.g., subsidies) associated with agriculture can benefit wildlife species, increasing predictability and availability of food. Avian scavengers including raptors often utilize subsidies associated with both recreational hunting and pest shooting on agricultural lands. However, these subsidies can contain lead (Pb) fragments if they are culled with Pb‐based ammunition, potentially leading to Pb poisoning and physiological impairment in wildlife. Nesting Golden Eagles ( Aquila chrysaetos ) commonly forage in agricultural lands during the breeding season, and therefore, both adults and their nestlings are susceptible to Pb exposure from scavenging shot wildlife. We assessed drivers of Pb exposure in 258 nestling Golden Eagles (401 total blood samples), along with physiological and growth responses, in agricultural lands across four western states in the United States. We also evaluated the birds’ Pb stable isotope signatures to inform exposure sources. Twenty‐six percent of Golden Eagle nestlings contained Pb concentrations associated with subclinical poisoning for sensitive species (0.03–0.2 μg/g ww), 4% had Pb concentrations that exceeded subclinical poisoning benchmarks (0.2–0.5 μg/g ww), and <1% exceeded either concentrations associated with clinical poisoning (0.5–1.0 μg/g ww) and or those deemed to cause severe clinical poisoning (>1.0 μg/g ww). Lead concentrations were highest in nestlings with close proximity to fields that potentially provided subsidies and declined exponentially as distance to subsidies increased. However, close proximity to agriculture, and presumably subsidies, positively influenced nestling growth rates. Across the range of Pb exposure, nestlings experienced a 67% reduction in delta‐aminolevulinic acid dehydratase (δ‐ALAD) activity, suggesting nestlings may have been anemic or experiencing cellular damage. Isotopic ratios of 206 Pb/ 207 Pb increased non‐linearly with increasing blood Pb in Golden Eagle nestlings, and 45% of the birds were consistent with those of ammunition. However, above 0.10 μg/g ww, the proportion associated with ammunition increased to 89% of the nestlings. An improved understanding of how these positive (growth) and negative (physiology) effects associated with proximity to subsidies interact would be beneficial to managers when considering management scenarios and potentially evaluating any measures taken to reduce Pb exposure across the landscape.

California, Idaho, Oregon, Wyoming↗

USGS2017

Correlates of immune defenses in golden eagle nestlings

An individual's investment in constitutive immune defenses depends on both intrinsic and extrinsic factors. We examined how Leucocytozoon parasite presence, body condition (scaled mass), heterophil-to-lymphocyte (H:L) ratio, sex, and age affected immune defenses in golden eagle ( Aquila chrysaetos) nestlings from three regions: California, Oregon, and Idaho. We quantified hemolytic-complement activity and bacterial killing ability, two measures of constitutive immunity. Body condition and age did not affect immune defenses. However, eagles with lower H:L ratios had lower complement activity, corroborating other findings that animals in better condition sometimes invest less in constitutive immunity. In addition, eagles with Leucocytozoon infections had higher concentrations of circulating complement proteins but not elevated opsonizing proteins for all microbes, and eagles from Oregon had significantly higher constitutive immunity than those from California or Idaho. We posit that Oregon eagles might have elevated immune defenses because they are exposed to more endoparasites than eagles from California or Idaho, and our results confirmed that the OR region has the highest rate of Leucocytozoon infections. Our study examined immune function in a free-living, long-lived raptor species, whereas most avian ecoimmunological research focuses on passerines. Thus, our research informs a broad perspective regarding the evolutionary and environmental pressures on immune function in birds.

California, Idaho, Oregon↗

USGS2017

Characterizing Golden Eagle risk to lead and anticoagulant rodenticide exposure: A review

Contaminant exposure is among the many threats to Golden Eagle ( Aquila chrysaetos ) populations throughout North America, particularly lead poisoning and anticoagulant rodenticides (AR). These threats may act in concert with others (e.g., lead poisoning and trauma associated with striking objects) to exacerbate risk. Golden Eagles are skilled hunters but also exploit scavenging opportunities, making them particularly susceptible to contaminant exposure from ingesting tissues of poisoned or shot animals. Lead poisoning has long been recognized as an important source of mortality for Golden Eagles throughout North America. More recently, ARs have been associated with both sublethal and lethal effects in raptor species worldwide. In this review, we examine the current state of knowledge for lead and AR exposure in Golden Eagles, drawing from the broader raptor contaminant ecology literature. We examine lead and AR sources within Golden Eagle habitats, exposure routes and toxicity, effects on individuals and populations, synergistic effects, and data and information needs. Continued research addressing data needs and information gaps will help with Golden Eagle conservation planning.

Journal of Raptor Research↗