Monitoring Anticoagulant Rodenticides in Birds of Prey in the Wildlife Rehabilitation Setting

Abstract

Monitoring anticoagulant rodenticide (AR) exposures in birds of prey presented to a wildlife clinic or rehabilitation setting has several advantages and disadvantages. Advantages include the ability to document signs of toxicosis in live birds. Additionally, in birds that die due to AR toxicosis, post-mortem lesions in the non-frozen, non-autolyzed cadaver will illustrate patterns of AR-induced hemorrhage. In birds that die or are euthanized due to other causes, liver samples can be collected and analyzed for AR residues. Disadvantages include an inability to ascertain the dose of AR ingested. In birds with exposure to multiple ARs, the timing of ingestion is also unknown. The route of exposure and pathway through the food chain likewise are unknown. Importantly, determining the true incidence of toxicosis and mortality among the sampled birds is not possible because birds that are found and transported for care may not be reflective of mortalities in the overall population. Despite the limitations of this method of sampling, much useful information can be gathered, particularly in studies that are continued over time. Two such monitoring studies conducted in Massachusetts, USA over a ten-year period, showing widespread exposure among sampled birds, will be discussed. In addition, other information that is needed to enhance the data obtained by cadaver sampling will be highlighted, particularly as these data gaps relate to evaluation of mitigation efforts.

What Do We Need to Know to Assess Individual and Population-level Effects on Wildlife from Anticoagulant Rodenticides?

“…The first group of papers in the Symposium presented information on the presence and prevalence of exposure by taxa, including raptors (Murray 2018) and other bird species (Vyas 2018); game animals (McMillin et al 2018) and mountain lions (Puma concolor) (Rudd et al 2018) in California; and domestic animals and wildlife in France. Animals sampled included live, injured raptors brought in to a wildlife clinic (Murray 2018); opportunistically-found carcasses and nuisance animals taken under depredation permits submitted to the California Department of Fish and Wildlife (CDFW) (McMillin et al 2018, Rudd et al 2018; carcasses and poison hotline call information submitted to a national database in France; and a compilation of data from published incident reports (Vyas 2018). The prevalence of rodenticide exposure ranged from none in deer (Odocoileus hemionus) in California, to very high percentages of the individuals tested for mountain lions in California and raptors in Massachusetts.…”