High Exposure Rates of Anticoagulant Rodenticides in Predatory Bird Species in Intensively Managed Landscapes in Denmark

Abstract

The extensive use of anticoagulant rodenticides (ARs) for rodent control has led to widespread secondary exposure in nontarget predatory wildlife species. We investigated exposure rates and concentrations of five ARs in liver samples from five raptors and six owls from Denmark. A total of 430 birds were analysed. ARs were detected in 84-100 % of individual birds within each species. Multiple AR exposure was detected in 73 % of all birds. Average number of substances detected in individual birds was 2.2 with no differences between owls and raptors. Difenacoum, bromadiolone, and brodifacoum were the most prevalent substances and occurred in the highest concentrations. Second-generation ARs made up 96 % of the summed AR burden. Among the six core species (sample size >30), summed AR concentrations were lower in rough-legged buzzard (Buteo lagopus) and long-eared owl (Asio otus) than in barn owl (Tyto alba), buzzard (B. buteo), kestrel (Falco tinnunculus), and tawny owl (Strix aluco). There was a strong tendency for seasonal variations in the summed AR concentration with levels being lowest during autumn, which is probably related to an influx of less-exposed migrating birds from northern Scandinavia during autumn. High hepatic AR residue concentrations (>100 ng/g wet weight), which have been associated with symptoms of rodenticide poisoning and increased mortality, were recorded high frequencies (12.9-37.4 %) in five of the six core species. The results suggest that the present use of ARs in Denmark, at least locally, may have adverse effects on reproduction and, ultimately, population status in some raptors and owls.

Poisoning by Anticoagulant Rodenticides in Humans and Animals: Causes and Consequences

“…macroscopic haemorrhages with no trauma) have been statistically characterised as representative of a high-risk toxic threshold [84]. According to these criteria, hepatic concentrations above 0.2 mg/kg have been associated with mortalities in raptors and small mustelids from Denmark [85], in raptors and hedgehogs from Mediterranean region of Spain [86], in six raptor species from Canary Islands, Spain [77].…”

Development of an Ecofriendly Anticoagulant Rodenticide Based on the Stereochemistry of Difenacoum

“…Because of this increased persistence in animal tissues, especially in liver (Langford et al, 2013), the use of SGARs is associated with an increased risk of secondary poisoning for predators and scavengers feeding on contaminated rodents. Evidence of secondary poisoning was confirmed in predatory bird species such as barn owl (Tyto alba), buzzard (B. buteo), kestrel (Falco tinnunculus), Red kyte (Milvus milvus), and tawny owl (Strix aluco) (Christensen et al, 2012 ;Hughes et al, 2013 ;Geduhn et al, 2015), in predatory mammals such as red foxes (Vulpes vulpes) (Sage et al, 2010), European mink (Mustela lutreola) (Fournier-Chambrillon et al, 2004), weasels (Mustela nivalis) (Elmeros et al, 2011). Therefore, ARs were identified by the European Union as candidates for future comparative risk assessment and substitution in view of their unacceptable risk of secondary poisoning for wildlife.…”

Shooting is still a main threat for raptors inhabiting urban and suburban areas of Rome, Italy

“…Beside these low occurrences, it is important to consider that several recent specific studies found high exposure to anticoagulant rodenticides in liver tissues of the raptor species (Thomas et al 2011;Christensen et al 2012;Coeurdassier et al 2012;Hughes et al 2013). Moreover, we need to acknowledge our limits in correctly identifying the poisoning and debilitation cases, not having performed toxicological tests.…”