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Wildlife Necropsy Reports

Diagnosing Causes of Fatalities in Wild Animals

DEC's Wildlife Health Unit (WHU) collaborate with Cornell University's College of Veterinary Medicine Animal Health Diagnostic Center (AHDC) to identify, monitor and respond to infectious and non-infectious diseases in free-ranging wildlife in New York State. (More information about this collaboration, including the 2011-2015 Wildlife Health Program Strategic Plan is available on DEC's Wildlife Health webpage). To identify causes of sickness and death in New York State's wild animals, the WHU performs necropsies (animal autopsies) and diagnostic laboratory tests. In an effort to promote public information sharing and communication, case reports and laboratory testing for cases of significant interest will be posted on this page.

Anticoagulant Rodenticides (mouse and rat poison) Found as Cause of Death in Three of Four Red-tailed Hawks in Manhattan, April 10, 2012

Summary of Necropsy Report

Four adult red-tailed hawks found dead in Manhattan during the months of February and March 2012 were recently examined. Three of the birds had evidence of spontaneous bleeding, but no sign of significant trauma or injury. The fourth bird died from complications due to egg laying (oviductal prolapse), possibly exacerbated by hemorrhaging. Toxicology tests for anticoagulant rodenticides (rat and mouse poison) revealed the presence of multiple compounds in the livers of three of the four birds. Difethialone was present in all birds and was the sole poison found in one of the hawks. In the other three birds, difethialone was accompanied by bromadiolone and brodifacoum rodenticides; diphacinone was also detected in one bird. The presence of anticoagulant rodenticide combined with spontaneous hemorrhaging indicates that rodenticide poisoning was the cause of death in three hawks. It could not be determined as the sole cause of death in the fourth hawk due to the reproductive related injuries it sustained.

Full Necropsy Reports and Screen Tests - Complete necropsy information and toxicology screen tests for each bird examined are in the following document: NYC 4 Red-Tailed Hawks - Anticoagulant Rodenticide Necropsy and Diagnostic Reports (PDF, 1.67 mb). Please be aware that the reports may include photos of actual necropsies and injured animals that may not be suitable for all viewers. For privacy, any personal information, such as names or addresses of the person(s) who reported or submitted carcasses were redacted from these reports.

Background of Rodenticides and Birds of Prey

Currently, anticoagulant rodenticides are the predominant class of pesticides used in products for rat and mouse control. These rodenticides interfere with vitamin K activity in the liver, which is essential for the production of factors that clot blood. Rodents that ingest a lethal dose of the poison will generally die of acute internal bleeding around 5-7 days later. During this time, if the rodent is eaten by a predator such as a hawk, the poison in the rat can cause the hawk to suffer the same abnormalities of blood clotting. If there is sufficient poison in the rat, the hawk may also die. Often, hawks or other scavengers will receive less than a lethal dose from a single rat, and go on to consume more poisoned rodents over time, resulting in multiple rodenticides in their system. Since the poisons may last in the body for months, it puts them at risk for bleeding excessively from routine injuries for long periods of time.

The primary compounds found in the affected NYC birds were "Second Generation Anticoagulant Rodenticides" or SGARS, which are more acutely toxic and physiologically persistent than first generation anticoagulants like warfarin, chlorophacinone and diphacinone. These qualities make SGARS more efficient killers of target rodents and greatly increase the threat to raptors and other carnivores that consume poisoned rodents. The Environmental Protection Agency (EPA) introduced regulations to limit the availability of SGARS to residential consumers; however, some products that are non-compliant with the EPA changes are still available because of ongoing legal challenges. To view these regulations, visit the EPA Pesticide Regulations website (link to the right)

Determining Cause of Death

Surveys in New York, and more recently in New England and Canada have shown that between 49% and 86% of raptors found dead from a variety of causes may have anticoagulant rodenticides in their system. The anticoagulants were determined to be the cause of death in only 5-15% of positive cases in these surveys. These surveys also revealed that levels detected were not a good predictor of diagnosis. Consequently, it can be difficult to determine when rodenticides are significant contributors to a bird's death.

Generally, rodenticide is considered the main cause of death when there is evidence of spontaneous internal bleeding (no sign of significant injuries) along with significant levels of anticoagulant rodenticide in the liver. Anticoagulants may also cause excessive bleeding in animals that have suffered routine injuries, and can contribute to the deaths of those animals. However, it can be more difficult to determine the role that anticoagulants play in these cases, particularly when there is no clear evidence of internal blood loss.

Other Methods to Control Rodent Problems

Control of rodents can be achieved without the use of SGARS by multiple approaches. Some basic approaches can be found on Cornell University's Integrated Pest Management website, and more specific rat control approaches can be found on the City of California Davis website (links to the right).

If poisoned bait is necessary, there are products available that are much less dangerous to pets and wildlife that may consume poisoned rodents. These, in combination with integrated pest management programs, will reduce secondary deaths in wildlife.

Additional Resources

Links to supplementary information on this topic can be found in the right-hand column of this page.