Changes in Detected Anticoagulant Rodenticide Exposure in Barn Owls ( Tyto alba) in Kentucky, USA, in 2012-16

Comparing anticoagulant rodenticide exposure in barn owl (Tyto alba) and common kestrel (Falco tinnunculus): A biomonitoring study in an agricultural region of southeastern Spain

Second-generation anticoagulant rodenticides (SGARs) are commonly used for rodent control, affecting various non-target wildlife species. Here, blood samples from common kestrels (Falco tinnunculus, n = 70 chicks) and barn owls (Tyto alba, n = 54 chicks and 12 adults) from Southeastern Spain were analysed using HPLC-TQ. SGAR prevalence was 68.6% in kestrel chicks, 50% in barn owl chicks and 100% in adult barn owls, with multiple SGARs in both species. Prothrombin time analysis in barn owls revealed a positive correlation with blood ΣSGARs, suggesting a potential adverse effect on coagulation. Analysis of variables potentially influencing SGAR prevalence indicated that, for kestrels, it was only related to the extent of artificial surface, showing no differences across study sites. In owlets, the highest prevalence occurred in the most urbanized study site, with human population density being a key factor. This study highlights species-specific differences in SGAR exposure, likely influenced by ecological traits. Barn owls probably encounter contaminated prey near anthropized areas, with widespread SGAR use and higher presence of target rodents. Conversely, kestrels, hunting a variety of prey often near human settlements, face consistently elevated exposure from multiple sources. Understanding these variations is crucial for effective conservation and minimizing SGAR impact on non-target wildlife.

Widespread use of anticoagulant rodenticides in agricultural and urban environments. A menace to the viability of the endangered Bonelli's eagle (Aquila fasciata) populations

Anticoagulant rodenticides (ARs) are one of the most toxic groups of compounds currently used worldwide for rodent pest control. Toxic baits are often, directly or indirectly, ingested by non-target animals, resulting in secondary poisoning and frequently affecting apex predators. Their presence in many species of raptors is quite common, particularly scavenger species, with some of these acting as sentinels for the presence of these substances in the environment. However, there is less data on the presence of ARs in Bonelli's eagle, one of the most endangered eagle species in Spain and which is experiencing a negative population trend in Europe. This medium-sized eagle feeds predominantly on live species, and rarely consumes carrion. In this study, 17 carcasses of Bonelli's eagles from the Eastern Spain were necropsied. Both first and second generation ARs in their livers were analyzed by HPLC-MS-TOF revealing that all the eagles studied had been exposed to at least 5 ARs, out of a total of 10 ARs analyzed, with 7 being the highest number of ARs detected in a sample. Second generation ARs were the most prevalent, particularly bromadiolone and brodifacoum, with the highest concentrations in 94% of the cases. More than a third of the eagles presented a liver concentration of greater than 200 ng/g ARs, suggesting AR poisoning. The elevated presence of these compounds in Bonelli's eagles could be a new cause of mortality for this species or could explain other causes of death, such as the increased mortality in power lines, and should be taken into account for their conservation. At the same time, the presence of these compounds in the environment also represents a risk to public health, as the most frequent species in the diet of Bonelli's eagle (rabbits and partridges) are also hunted and consumed by hunters and their families.

Anthropogenic threats to owls: Insights from rehabilitation admittance data and rodenticide screening in Texas

Owls (Strigiformes) provide myriad ecosystem services and are sentinels for ecosystem health. However, they are at continued risk from anthropogenic threats such as vehicle collisions, entanglement with human-made materials, and exposure to anticoagulant rodenticides (ARs), a widespread pesticide known to affect owls. Texas is an important region for numerous migratory and non-migratory owl species in the United States (US), yet assessments of threats owls face here are lacking preventing the development of informed conservation strategies. This study coupled assessment of admittance data from two wildlife rehabilitation centers in Texas with AR liver screening to (1) identify which species of owls are commonly admitted, (2) evaluate seasonality of admittance, and (3) assess causes of admittance for owls in Texas. Between 2010 and 2021, 1,620 owls were admitted into rehabilitation, representing eight species of which the Great-horned Owl (Bubo virginianus) was the most common. For all owls combined admittance rates were highest in the spring, driven by an influx of juveniles (n = 703, 43.40%). The leading cause of admittance amongst species was 'no apparent injury' (n = 567, 34.94%). Where clear diagnoses could be made, the leading causes of admittances were 'entrapment in human infrastructure' (n = 100, 6.11%) and 'collision with vehicles' (n = 74, 4.56%). While the admittance data did not reveal any cases of AR poisoning, liver screening demonstrated high incidences of AR exposure; of 53 owls screened for ARs, 50.94% (n = 27) tested positive with 18 showing exposure to multiple ARs. Brodifacoum was the most frequently detected AR (n = 19, 43.18%) and seven owls (25.93%) tested positive within lethal ranges. Our results suggest that owls in Texas are at risk from myriad anthropogenic threats and face high exposure rates to ARs. In doing so, our results can inform conservation strategies that mitigate anthropogenic threats faced by owls in Texas and beyond.

Prevalence of anticoagulant rodenticide exposure in red-tailed hawks (Buteo jamaicensis) and utility of clotting time assays to detect coagulopathy

Anticoagulant rodenticides (ARs) continue to be used across the United States as a method for controlling pest rodent species. As a consequence, wild birds of prey are exposed to these toxicants by eating poisoned prey items. ARs prevent the hepatic recycling of vitamin K and thereby impede the post-translational processing of coagulation factors II, VII, IX, and X that are required for procoagulant complex assembly. Through this mechanism of action, ARs cause hemorrhage and death in their target species. Various studies have documented the persistence of these contaminants in birds of prey but few have attempted to use affordable and accessible diagnostic tests to diagnose coagulopathy in free-ranging birds of prey. In our study free-ranging red-tailed hawks were found to be exposed to difethialone and brodifacoum. Eleven of sixteen (68%) livers tested for AR exposure had detectable residues. Difethialone was found in 1/16 (6%), and brodifacoum was detected in 10/16 (62%) liver samples that were tested for rodenticide residues. Difethialone was found at a concentration of 0.18 ug/g wet weight and brodifacoum concentrations ranged from 0.003-0.234 ug/g wet weight. Two out of 34 (6%) RTHA assessed for blood rodenticide had brodifacoum in serum with measured concentrations of 0.003 and 0.006 ug/g. The range of clotting times in the prothrombin time (PT) and Russell's viper venom time assays for control RTHA were 16.7 to 39.7 s and 11.5 to 91.8 s, respectively. One study bird was diagnosed with clinical AR intoxication with a brodifacoum levels in blood of 0.006 and 0.234 ug/g wet weight in blood and liver respectively, a packed cell volume (PCV) of 19%, and PT and RVVT times of >180 s. No correlation was found between PT and RVVT in the control or free-range RTHA, and there was no relationship found between the presence of liver anticoagulant residues and clotting times in the PT and RVVT.

Anticoagulant rodenticide exposure and toxicosis in bald eagles (Haliaeetus leucocephalus) and golden eagles (Aquila chrysaetos) in the United States

Raptors, including eagles, are geographically widespread and sit atop the food chain, thereby serving an important role in maintaining ecosystem balance. After facing population declines associated with exposure to organochlorine insecticides such as dichlorodiphenyltrichloroethane (DDT), bald eagles (Haliaeetus leucocephalus) have recovered from the brink of extinction. However, both bald and golden eagles (Aquila chrysaetos) are exposed to a variety of other toxic compounds in the environment that could have population impacts. Few studies have focused on anticoagulant rodenticide (AR) exposure in eagles. Therefore, the purpose of this study was to determine the types of ARs that eagles are exposed to in the USA and better define the extent of toxicosis (i.e., fatal illness due to compound exposure). Diagnostic case records from bald and golden eagles submitted to the Southeastern Cooperative Wildlife Disease Study (University of Georgia) 2014 through 2018 were reviewed. Overall, 303 eagles were examined, and the livers from 116 bald eagles and 17 golden eagles were tested for ARs. The percentage of AR exposure (i.e., detectable levels but not associated with mortality) in eagles was high; ARs were detected in 109 (82%) eagles, including 96 (83%) bald eagles and 13 (77%) golden eagles. Anticoagulant rodenticide toxicosis was determined to be the cause of mortality in 12 (4%) of the 303 eagles examined, including 11 bald eagles and 1 golden eagle. Six different AR compounds were detected in these eagles, with brodifacoum and bromadiolone most frequently detected (81% and 25% of eagles tested, respectively). These results suggest that some ARs, most notably brodifacoum, are widespread in the environment and are commonly consumed by eagles. This highlights the need for research to understand the pathways of AR exposure in eagles, which may help inform policy and regulatory actions to mitigate AR exposure risk.

Temporal Persistence of Bromadiolone in Decomposing Bodies of Common Kestrel (Falco tinnunculus)

Bromadiolone is a second generation anticoagulant rodenticide (SGAR) used to control pest rodents worldwide. SGARs are frequently involved in secondary poisoning in rodent predators due to their persistence and toxicity. This study aims to evaluate the persistence of bromadiolone in liver at different stages of carcass decomposition in experimentally-dosed common kestrels (Falco tinnunculus) to understand the possibility of detecting bromadiolone in cases of wildlife poisoning and the potential risk of tertiary poisoning. Twelve individuals were divided into the bromadiolone-dose group (dosed with 55 mg/kg b.w) and the control group. Hepatic bromadiolone concentrations found in each stage of decomposition were: 3000, 2891, 4804, 4245, 8848, and 756 ng/g dry weight at 1–2 h (fresh carcass), 24 h (moderate decomposition), 72 h, 96 h (advanced decomposition), seven days (very advanced decomposition), and 15 days (initial skeletal reduction) after death, respectively. Liver bromadiolone concentrations in carcasses remained relatively stable over the first four days and raised on day 7 of decomposition under the specific conditions of this experiment, presenting a risk of causing tertiary poisoning. However, at the initial skeletal reduction stage, liver bromadiolone concentration declined, which should be considered to interpret toxicological analyses and for proper diagnosis. This experimental study provides for the first time some light to better understand the degradation of SGARs in carcasses in the wild.