The top four causes of death of a red-tailed hawk are emaciation (starvation), trauma, toxicoses, and disease¹. In recent years there has been a large focus on research into the diseases and toxicological agents assailing red-tailed hawks. Red-tailed hawks are the most abundant raptor in North America². As such, it stands to reason that toxicological research on raptors would use these animals as subjects of study.

Red-tail hawks are birds of prey. As mentioned in the previous blog post, their diet consists primarily of small mammals, typically rodents, and small birds. As a result of feeding mostly on other wildlife, red-tails are subject to the risk of ingesting potentially damaging compounds. The use of rodenticides by humans to control pest species of small mammals has had cascading consequences for non-target organisms³. There are particular rodenticides that are in common use that have serious health impacts on secondary consumers. One rodenticide in particular is brodifacoum, a molecule that inhibits a vitamin K pathway that is essential for activation of blood clotting factors II, VII, IX, and X^3,4. Some of the symptoms of primary and/or secondary consumers include somnolence, loss of or decrease in appetite, decreased movement and perception, and weakness⁴. These effects are mild compared to the lethal effects of the compound, which can include tachycardia (irregular heartbeat), hypo/hyper-thermia, vomiting, vomiting of blood, hemorrhaging from the: skin, mucosal membranes, anterior of the eye, any open wound, nose, ear, and in some cases in the pulmonary system⁴. It has been documented in red-tail hawks suffering from brodifacoum intoxication that treatment and recovery are possible³.

Brodifacoum

In 2008, DVM’s (Doctor of Veterinary Medicine) Murray and Tseng were charged with the care of a red-tail hawk brought in for an inability to fly, from a suburban neighbourhood. The bird was unresponsive, dehydrated, and in near critical condition³. Moreover the hawk had a cut on the shoulder with bruising that would not stop bleeding. Dr.’s Murray and Tseng estimated anticoagulant poisoning as the cause of the hawks condition and treated it with medications including vitamin K, treatment in an oxygen chamber, and a pressure bandage for the shoulder wound. Blood tests were run and it was confirmed that the hawk was suffering from secondary rodenticide anticoagulant intoxication. The hawk’s condition began to improve and was hand fed until day 5 of treatment, afterward it regained the strength to eat on its own. After 1 week the hawk was moved to an aviary to alleviate stress and after 21 days was moved to an open air aviary. Six weeks after admittance the hawk was declared healthy and re-released after being banded³.

While the effects of anticoagulant rodenticides are known and are clearly treatable, there seems to be no general consensus about what doses constitute lethal or dangerous levels in most raptor species other than barn owls⁵. Exposure levels of raptors in Canada to anticoagulant rodenticides were examined briefly in 2011⁵.  Most raptor species that are common across Canada and the northern United States that feed on rodents are exposed at some point, to anticoagulant rodenticides⁵. In 2011 Thomas et al. collected liver samples from 5 raptor species across various parts of Canada and the northern U.S.⁵. The raptors sampled were not selected solely for rodenticide poisoning death diagnoses, but were chosen to best represent a wide array of fatalities⁵. The results of the chemical analysis showed that great horned owls across Canada are exposed to the highest levels and widest array of anticoagulant rodenticides, followed by red-tailed hawks⁵. The study estimates that on average 11% of great horned owl fatalities in Canada are a result of anticoagulant rodenticides, and suggest that red-tailed hawks are even more sensitive than that⁵.

The 1979 moratorium on DDT saw peregrine falcon populations rebound from endangered to non-threatened⁶. This success story underlines the importance of the ecological assessment of potential pesticide use. While DDT was a crop insecticide applied on industrial scales, anticoagulant rodenticides are applied in large quantities in private, rural, and urban environments often visited by raptors⁴. As anticoagulant rodenticides are relatively long lived poisons and are easily transferred to non-target organisms⁵, their effects on raptor populations should be taken into account when chemical pest control methods are applied. As red-tailed hawks are one of the most common raptors in North America and the largest portion of their diet consists of small mammals, it is reasonable to assume that continued increase in the use of anticoagulant rodenticides will be a large detriment to the species.

To avoid unnecessary intoxication of raptors by anticoagulant rodenticides, I implore you, the reader, to seek alternative measures for rodent pest control that do not have far reaching, potentially lethal consequences for one of North Americas most well-known raptors.

References:

1. Franson, JC; Thomas, NJ; Smith, MR; et al. (1996) A retrospective study of postmortem findings in red-tailed hawks. Journal of Raptor Research. 30, 1, 7-14. https://sora.unm.edu/sites/default/files/journals/jrr/v030n01/p00007-p00014.pdf
2. Johnsgard, P.A., (1990) Hawks, Eagles, & Falcons of North America. Smithsonian Institution Press, Washington and London.
3. Murray, M, and Tseng, F., (2008) Diagnosis and treatment of secondary anticoagulant rodenticide toxicosis in a red-tailed hawk (Buteo jamaicensis). Journal of avian   medicine and surgery 22, 1, 41-46.http://www.jstor.org.ezproxy.viu.ca/stable/pdf/30134203.pdf?acceptTC=true
4. Valchev, I., et al., (2008) Anticoagulant rodenticide intoxication in animals–a review. Turkish Journal of Veterinary & Animal Sciences 32, 4, 237-243.http://dd6db2vc8s.search.serialssolutions.com/?ctx_ver=Z39.88-2004&ctx_enc=info%3Aofi%2Fenc%3AUTF-8&rfr_id=info:sid/summon.serialssolutions.com&rft_val_fmt=info:ofi/fmt:kev:mtx:journal&rft.genre=article&rft.atitle=Anticoagulant+rodenticide+intoxication+in+animals&rft.jtitle=Turkish+Journal+of+Veterinary+and+Animal+Sciences&rft.au=NIKOLOV%2C+Yordan&rft.au=VALCHEV%2C+Ivan&rft.au=BINEV%2C+Rumen&rft.au=YORDANOVA%2C+Veska&rft.date=2008&rft.pub=T%C3%9CB%C4%B0TAK&rft.issn=1300-0128&rft.volume=32&rft.issue=4&rft.spage=237&rft.epage=243&rft.externalDocID=85071&paramdict=en-US
5. Thomas, P. J., et al., (2011) Second generation anticoagulant rodenticides in predatory  birds: probabilistic characterisation of toxic liver concentrations and implications for predatory bird populations in Canada. Environment International 37, 5, 914-                http://www.sciencedirect.com.ezproxy.viu.ca/science/article/pii/S0160412011000614
6. Ydenberg, R.C., et al., (2004) Western sandpipers have altered migration tactics as peregrine falcon populations have recovered. Proceedings of the Royal Society of       London, Series B: Biological Sciences 271, 1545, 1263-1269.   http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1691718/?tool=pmcentrez