Raptors and Rodenticides
The conclusion of a research project is always exciting, not only because we can finally share the results of our efforts, but because we look to the future and plan what we can do next. Our raptors and rodenticide project started in 2019, and you may recall reading about our project and preliminary results in the Healthy Wildlife blog: (http://blog.healthywildlife.ca/summer-research-project-raptors-and-rodenticides/).
To briefly summarize our project: in the summer of 2019, we analyzed the livers of deceased birds of prey submitted to the CWHC for residues of rat poisons. The most common group of commercially available rat poisons contain second-generation anticoagulant rodenticides (SGARs). When the target rodent, like a rat or mouse, eats the bait containing SGARs, the SGARs interfere with the clotting cascade required for hemostasis, and cause death in the rodent by hemorrhage.
We know that SGARs are very effective at causing death in rodents but we do not know what happens to the birds of prey that eat these poisoned rodents. Over its lifetime, a bird of prey will eat thousands of rodents, and if some of them are poisoned with SGARs, the bird will be indirectly poisoned as well. The residues accumulate in body tissues, and can be measured using specific techniques. Using mass-spectrometry techniques in collaboration with the Animal Health Laboratory at the University of Guelph, we measured the levels of 14 different anticoagulant rodenticides in 133 raptors.
Our final results and analysis has been published in the Journal of Environmental Science and Pollution Research (https://link.springer.com/article/10.1007/s11356-022-18529-z).
- We found residue of anticoagulant rodenticides in 62% (82/133) of sampled raptors.
- Of the positive birds, 42% (34/82) contained more than one residue, likely indicating the bird has been exposed multiple times.
- 12/17 species of sampled raptors contained residue of anticoagulant rodenticides
- We found AR residues in species of hawks, owls, eagles, and falcons – all groups we sampled BUT osprey.
- We found AR residue in peregrine falcons, kestrels, and merlins – unexpected because their primary prey items are not rodents.
Our results demonstrate that anticoagulant rodenticide residues are common in Ontario raptors. This is concerning for many reasons. For some birds, the results were not unexpected – both great horned owls and red-tailed hawks are generalist predators, meaning they will eat nearly anything they are able to catch, and would certainly be expected to consume some rats or mice in their lifetime. Other species, like peregrine falcons, bald eagles, and American kestrels, tested positive for anticoagulant rodenticide residue, but don’t generally consume rats and mice as their prey. The routes of secondary exposure for these species, that do not include rodents, are beginning to be more defined in the scientific community, and may involve slugs, small songbirds, and storm water overflow impacting freshwater fish. Integrative pest management, including the proper storage of food to discourage rodent and pest presence and environmental planning can help to reduce the need for anticoagulant rodenticides.
This research was funded by the Ontario Animal Health Network (OAHN) and supported by the CWHC. We are grateful to the wildlife rehabilitation organizations, wildlife biologists, and members of the public who submitted carcasses to the Canadian Wildlife Health Cooperative (CWHC), especially Fatal Light Awareness Program (FLAP) Canada, the Owl Foundation, Shades of Hope Wildlife Refuge, and the Toronto Wildlife Centre.
For upcoming details about this project, visit www.cwhc-rcsf.ca and www.oahn.ca. Visit the CWHC website to learn more about wildlife disease surveillance and how you can contribute to our ongoing research efforts.
Submitted by Grace Thornton
Thornton, G.L., Stevens, B., French, S.K., Shirose, L.J., Reggeti, F., Schrier, N., Parmley, E.J., Reid, A. and Jardine, C.M., 2022. Anticoagulant rodenticide exposure in raptors from Ontario, Canada. Environmental Science and Pollution Research, pp.1-10.