Summer Research Project: Raptors and Rodenticides.

I love urban wildlife, those animals that refuse to let humans remove them from their habitat. Some urban environments seem totally incompatible with wildlife, yet some animals carve out a niche for themselves and thrive despite our best human efforts to discourage them.

Unfortunately, not everyone feels the same way about these resilient animals with which we share our habitat. Pest control companies run a busy business ridding our homes, businesses, and farms of some less-than appreciated “pests” including rats, raccoons, and squirrels. Rodenticides, acutely toxic compounds, are central to many pest control methods. Anticoagulant rodenticides (ARs) work by antagonizing the vitamin K-dependent clotting cascade, resulting in often-fatal hemorrhage. Some of these compounds, either first or second generation anticoagulation rodenticides (FGARs or SGARs) have long half lives, and accumulate mainly in the liver of the target wildlife that consume them via flavored rodent baits. Unfortunately, these ARs also pose a threat to non-target wildlife, the predator that consumes the poisoned pests.

Grace Thornton working in the necropsy laboratory.

My summer project is to assess the exposure of raptors to anticoagulant rodenticides in southern Ontario. We are testing raptors routinely submitted to the Canadian Wildlife Health Cooperative and those obtained from wildlife rehabilitation facilities across the province. Results are pending on this project as we are aiming to collect raptor carcasses through the 2019 fall migration.

We have currently received results for 50% of our target sample size. Preliminary results demonstrate that 59% of the tested raptors are positive for the presence of at least one AR, and 25% of raptors tested demonstrated the presence of more than one AR, either brodifacoum, bromadialone, or difethialone. Since 2013, these three SGARs have been restricted for use in Canada by a licensed commercial applicator. The United States Environmental Protection Agency (EPA) regards brodifacoum and difethialone as the ARs that may pose the most risk to non-target wildlife (US EPA 2004).

Designing this project has been invaluable experience, improving my communication with the public, allowing me to practice my anatomy and post-mortem skills I gained from first year vet school, and gain experience with pathology, diseases, and parasites that will be useful in the coming years.

A regular day could have me reading peer-reviewed journals, organizing data in spreadsheets, contacting wildlife rehabbers to coordinate the shipping of carcasses, conducting post-mortem exams and removing liver samples for testing, or assisting on one of the many CWHC cases passing through the post-mortem room this summer. I’m grateful to have such a supportive and knowledgeable group of people around me at the CWHC ON/NU branch as I learn more about the role of wildlife disease surveillance in Canada, conducting an effective surveillance program, and biosecurity challenges.

The Ontario Animal Health Network provided funding for this project, and we are thankful for the submission of carcasses and support of this project from FLAP Canada, the Owl Foundation, Shades of Hope Wildlife Refuge, and the Toronto Wildlife Center.



For upcoming details about this project, visit and





US EPA (2004). Potential risks of nine rodenticides to birds and nontarget mammals: a comparative approach. Washington DC, USA.


Submitted by:

Grace Thornton

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