Bobcats and Deer In A Changing Ecosystem
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Kiawah Island is an extraordinary place, boasting world-class amenities, a pristine beach, and a vibrant natural ecosystem. For many years, the island’s ecosystem has functioned just like Mother Nature intended. Sea turtles nested on our beaches, ospreys caught fish in our creeks, and bobcats controlled the island’s deer population by preying on fawns each spring. While the Kiawah ecosystem is still healthy in many regards, Town Biologists have seen some disturbing trends in our bobcat and deer populations over the last few years. In this article, we will discuss these trends, how residents can help, and why the Town has decided to move forward with a deer harvest program this fall.
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Population
Kiawah is world-renowned for its bobcat population. Filmmakers from all over the world have visited the island to showcase our bobcats. Town Biologists have gathered incredible amounts of data on bobcat behavior and movements through the
Town’s Bobcat GPS Research project
. Unfortunately, over the last three years, Biologists have noticed a decline in bobcat numbers. This decline is likely due to two main factors, habitat loss, and rodenticide poisoning.
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Habitat Loss
While Kiawah still has plenty of excellent bobcat habitat, it has less than it did ten years ago. This means that bobcats have to travel further and expand their home range size to meet their needs. Because bobcats are territorial, larger home range sizes mean fewer bobcats on the island. Also, increased travel by bobcats makes them more susceptible to vehicle collisions and other mortality events.
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Secondary poisoning from second-generation anticoagulant rodenticides (SGAs) is a significant problem worldwide. SGAs are many times more toxic than alternative rodenticides, and because SGAs don’t kill immediately, the rodent continues to consume the bait, accumulating super-lethal concentrations of the poison. Once a bobcat, hawk, owl, or other predator eats these poisoned rodents, the SGAs begin to build up in their body. Since SGAs can persist for up to a year inside the body, predators can quickly accumulate a lethal dose if they continue to feed on poisoned rodents.
In August of 2019, an adult female bobcat was found dead from rodenticide poisoning near Seascape Villas. Tests showed that she had lethal levels of four different SGAs in her system. This was the eighth known bobcat death in the last two years. Although some of these deaths were from other causes such as vehicle collisions, the impacts of rodenticide poisonings are likely very significant.
To try to quantify these impacts, Town Biologists teamed up with local researchers and a veterinarian to collect blood samples from bobcats this winter during our annual trapping efforts for the Bobcat GPS study. Biologists were able to capture only four bobcats this winter in five weeks of trapping, which is a substantially lower capture rate than in prior years. Blood samples were analyzed for a variety of parameters, including exposure to SGAs. Results showed that one out of the four bobcats had recently consumed SGAs. Because SGAs only persist in the blood for two to three weeks, it doesn’t rule out prior SGA exposure and impacts to the other three bobcats that tested negative. SGAs accumulate in the liver over time, and while this is not always fatal, it can cause reproductive and immune problems.
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White-tailed deer are very adaptable creatures and a common sight in suburban communities all over the country. Deer are a prey species, which means their survival strategy is to continually produce offspring since predators will eat many of them. Deer and other prey species cannot regulate their numbers. Because of the lack of natural predators in most suburban communities, deer populations can proliferate and become overabundant. Kiawah has been the exception to this rule for many years as our deer population has been naturally controlled and maintained by bobcats.
Kiawah’s declining bobcat numbers have allowed the island’s deer population to rise quickly. Town Biologists monitor Kiawah’s deer population by conducting biannual spotlight surveys. These surveys have shown an increase in fawn survival and an overall increase in the island’s deer po
pulation by 58% in the last two years. This increasing trend in deer numbers will likely continue unless a deer management program is initiated. Fo
r this reason, Town Council discussed and approved the development and implementation of a deer harvest program at the April 7 Town Council meeting.
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The program will be conducted by Town Biologists and is scheduled to begin this fall. Deer will be harvested throughout the island, with a focus on areas with the highest deer concentrations and the highest incidence of deer-vehicle collisions. Work will be conducted under a State permit during nighttime hours using suppressed weapons. All harvested deer will be processed, and the meat will be donated to local food banks or shelters. The goal of the program is to reduce the deer population to a density of 80 deer per square mile (2019 density is 111). To maintain reduced deer numbers, it will likely be necessary to conduct a deer harvest annually for the next few years. Biologists are hopeful that bobcat numbers will rebound quickly and will once again be able to keep the island’s deer herd stable, eliminating the need for an annual deer harvest.
How you can help
- Create habitat for bobcats by adding native plants to your landscaping. Focus on understory plants that provide dense cover. Let buffer areas grow back naturally. Support the Town’s Grow Native initiative.
- Rethink your rodent control strategy. Rodents seen in yards or on porches are likely native species that do not cause damage inside homes. These rodents are vital food for bobcats and other predators.
- Never use a second-generation anticoagulant rodenticide. These include: Brodifacoum, Bromadiolone, Difenacoum, and Difethialone.
- Do not feed deer.
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