The Red-tailed Hawks of Central Park and Secondary Poisonings: Part I

By Marcia Anderson

Two of the young red-tailed hawk hatched from a nesting couple in Central Park, New York City, have recently been diagnosed with cases of poisoning from rodent baited traps set out in neighboring properties. The two eyasses, were captured, diagnosed and treated for secondary poisoning.

What is primary versus secondary poisoning? Primary poisoning refers to poisoning resulting from eating a bait. Secondary poisoning occurs when eating another animal that has been poisoned, such as a bird eating a rat containing residues of a rodenticide.

Red-talked hawk nest (image c/o D. Bruce Yolton)

People often forget to think about the fact that once the animal they have targeted has eaten poison, that animal itself now becomes poison for any other animals which may eat it. In other words, if your dog or cat eats a poisoned mouse they too will now have ingested the poison as secondary poisoning. Each year countless pets, wildlife, even beautiful eagles and hawks die from secondary poisoning. You do not want to be responsible for the death of the wrong animal via poisoning.

The problem with poisoning rodents is that it doesn’t kill them fast enough. Poisoning produces a slow death for any animal which may ingest it. Anti-coagulants contain chemicals that limit blood clotting and can take up to 2 weeks to kill the animal. The rodents wander aimlessly for hours before dying… easy prey for a hungry wild mammal or raptor. Secondary poisoning is just as serious as primary poisoning; as the animal is too sick to hunt or fly, and will often starve to death (secondary victims are often the young, who once back at the den or nest will become disoriented, lethargic, and will starve to death or fall prey to other predators). These two young hawks were very lucky, as they and their parents are very high profile residents of Central Park and concerned citizens noticed the changes in their behavior and help was timely provided.

The question is: Which birds and mammals are at risk? The risk of poisoning is greatest for predatory and scavenging birds and cats.

How do we reduce the risk of primary or secondary poisoning? Primary poisoning can be reduced by the use of bait stations and smart baiting strategies. Secondary poisoning may be  prevented by choosing poisons that are non-persistent. Cyanide, cholecaliferol and diphacinone do not usually cause secondary poisoning. Brodifacoum and superwarfarin rodenticides do, so special care with its application by licensed professional applicators is important.

Regular inspections should be carried out to search for rodent bodies, both during and after the treatment period. Many rats will not die until several days after eating the bait and can be found up to 300ft. or more away from the bait site.  Although many rats die underground, it is crucial to search for bodies at the surface and under any cover, so that scavengers do not find them and become victims of secondary poisoning

Part II will discuss reducing the rat populations via Integrated Pest Management (IPM) .

About the Author: Marcia is the bed bug and vector management specialist for the Pesticides Program in Edison. She has a BS in Biology from Monmouth, second degree in Environmental Design-Landscape Architecture from Rutgers, Masters in Instruction and Curriculum from Kean, and is a PhD in Environmental Management candidate from Montclair – specializing in Integrated Pest Management and Environmental Communications. Prior to EPA, and concurrently, she has been a professor of Earth and Environmental Studies, Geology and Oceanography at Kean University for 14 years.

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