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Jul 28 2020

A Declining Population

By Jim Jordan, Wildlife Biologist, for The Island Connection

Kiawah’s bobcats and other wildlife are facing a new threat that is causing substantial harm to the entire island ecosystem. The threat comes from the use of certain highly toxic rodenticides –  pesticides used to control rats and mice – known as second generation anticoagulants.

Anticoagulant rodenticides work by inhibiting the body’s recycling of Vitamin K, which is vital to the blood clotting process. Infected rodents ultimately bleed to death three to seven days after consuming the poison.

Bobcats and other predators accumulate these rodenticides by feeding on these dying or dead rodents, a process called secondary poisoning.

Kiawah is world-renowned for its bobcat population, which historically was one of the healthiest, densest populations in the country. Kiawah has the longest continuous study on bobcats in the world, and our bobcats have been tracked annually using GPS collars since 2007.

 Beginning in 2017, we saw an increase in bobcat deaths on the island and a noticeable decrease in their numbers. On Aug.1, 2019, an adult female bobcat was found dead near a villa complex on the island. The carcass was sent to the Southeastern Cooperative Wildlife Disease Study at the University of Georgia. The cause of death was “anticoagulant rodenticide toxicosis (brodifacoum, bromadiolone, difethialone and diphacinone toxicity; difenacoum exposure).”

While the secondary effects of second-generation anticoagulants are well-documented across the world, this was the first evidence of an issue here at Kiawah. We began a public awareness campaign to inform the public of the potential risk to bobcats and other predators from SGAs. We provided information and suggestions for managing rodent issues without the use of SGAs, such as exclusion, traps and following integrated pest management guidelines. This information was sent to residents, entities, regimes and pest control companies. We received voluntary compliance to stop using SGAs from many residents, our major entities and a handful of pest control companies. 

Beginning in February of 2020, we collected blood samples from bobcats captured during our GPS study. Because of the drastic decline in their numbers, we were only able to capture four bobcats. Since SGAs only persist in the bloodstream for days after exposure, this is not a great technique to look at exposure rates in the population, but, nevertheless, one of these four bobcats did show recent exposure to brodifacoum, an SGA.

 Based on the steep decline in bobcat numbers, the subsequent rise in deer numbers – bobcats have historically controlled Kiawah’s deer population by preying on fawns – and the evidence that SGAs were the cause of at least one bobcat death, the town planned to discuss and potentially enact an ordinance to ban all SGA use. On April 6, 2020, the town was notified by the South Carolina Department of Pesticide Regulation that it was prohibited by state law from regulating pesticides in any manner.

Based on that communication, the Town Council elected not to take any action on the ordinance. The town was hopeful that our public education campaign was making a difference, but that does not appear to be the case.

 Two out of the four bobcats captured this winter have already died due to anticoagulant rodenticide poisoning. The first was an adult male found dead on May 19, 2020. The second was an adult female found dead on June 10, 2020. The second incident was particularly tragic as this female died during labor, along with her four kittens.

Recent results confirm that the extensive use of SGAs is a significant issue for Kiawah’s bobcats and is directly responsible for at least seven bobcat deaths in the last year. Kiawah’s once healthy bobcat population is now estimated at 10 or fewer, down from a historic population of 30 to 35. If we are unable to get this problem under control and continue to lose bobcats, they likely won’t be able to successfully breed and produce viable offspring. Even if the small number remaining do successfully produce offspring, they would be doing so in a genetic bottleneck. This effectively means that the resulting offspring and future generations would be a product of inbreeding and would have diminished survival. This is one of the mechanisms that causes isolated animal populations to become extirpated.

Bobcats are the top predator on Kiawah Island and provide vital natural control for our island’s deer and rodent populations. Fewer bobcats mean more deer and more rodents. The rise in deer numbers has forced the town to implement a deer management program to control their numbers for the first time in our history. Also, since SGAs are likely to have negative secondary effects on all animals that consume rodents, their continued use will likely lead to an increase in rodent populations in the future.

What’s being done

The town and Kiawah Conservancy have requested a temporary, one-year prohibition on SGA use on Kiawah Island from the South Carolina Department of Pesticide Regulation. This request is currently being evaluated, and, if granted, would immediately remove these products from our ecosystem and mitigate any further damage to our bobcat population as well as other wildlife while our community works on a permanent solution to this issue.

The town is also working closely with the pest control companies, the South Carolina Pest Control Association and the Department of Pesticide Regulation to increase education and training for local pest control companies.

How can you help?

Eliminate the toxic foursome.

Tell your pest control provider not to use second-generation anticoagulant rodenticides on your property. These include: brodifacoum, bromadiolone, difenacoum and difethialone.

Be Informed

Pest control companies are required to disclose the active ingredients in all pesticides they are using. Ask your pest control provider to provide in writing what they are using on your property.

Tell your provider never to use any of the toxic SGAs on your property and require that they follow an integrated pest management strategy and only use pesticides as a last resort.

Integrated Pest Management

IPM is an effective pest management strategy and will help the island’s bobcat population recover. It requires a thorough survey of the property to identify specific rodent problems and entry points and ways in which residents are unintentionally attracting rodents. If rodents are inside a home or other structure, nonlethal methods including exclusion, eliminating food and water sources and traps are used.

Pesticides are the last resort and, if necessary, should only be used for 10 days or until the problem animals have been eliminated.

If pesticides are necessary, first generation anticoagulants – warfarin, chlorophacinone and diphacinone – are better than second-generation anticoagulants but still have secondary effects on wildlife. The best option would be a product that uses bromethalin or cholecalciferol. While these products have significantly lower secondary effects on bobcats and other predators, they are still potentially toxic if consumed directly by pets and can only be used inside of a tamper-resistant bait station.

Federal law requires that all rodenticide packaging clearly display the active ingredients and instructions for use. Failure to follow the instructions on the label is a violation of state and federal law. Always check the label before using any rodenticide product.

Become a Bobcat Guardian

The town has received an inspiring amount of support for our bobcats and is introducing a new initiative to mobilize that passion through our Bobcat Guardian program, which encourages residents, businesses and pest control companies to publicly pledge never to use an SGA.

Signers of the pledge will be listed on the town’s website as Bobcat Guardians and recognized for their commitment to saving Kiawah’s bobcats. Visit savekiawahsbobcats.com for more information and to take the pledge.

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