While it’s ticks galore on the mainland, it’s quite a different story on Shelter Island. It’s been known since the late 1980s and early 1990s that if you reduce the deer population you reduce the population of ticks. When I worked on Fishers Island for the Southold Town Trustees in 1989 I would take my “tick flag” along with me and every once in a while between site inspections, drag it over the vegetation here and there. The results amazed me. I would get an occasional dog tick, the big one of the three common ones, but nary a deer tick, the one that gave me and half of the resident population on Shelter Island Lyme disease. It wasn’t until late in my tenure there that I found out the reason — no deer.
In the 1980s and early 1990s deer ticks were rampant throughout East Hampton Town. In 1992 and 1993 a third tick began to show up on my one-meter-square white cotton flag, the Lone Star tick, but only in Montauk and once on Gardiner’s Island. The Southern Lone Star, so named because of the white spot on the back of the female, was a latecomer to the area. Now it is the most populous of all and is found on Long Island wherever there are deer.
In 2005 Cornell University’s natural resources department, with help from Cornell Cooperative Extension, the Suffolk County’s Office of Vector Control, and the New York State Department of Environmental Conservation initiated an experiment on Shelter Island (and part of Fire Island) that would change the direction of tick population growth from up to down. After three years of pre-study, “four-poster” baited deer stations were deployed throughout the island in 2008. The four-poster is a unique setup that provides food to the deer while at the same time applying a “tickiside,” permethrin, to the deer’s neck with rollers.
A comparable number of areas without the devices were used as control areas, against which the results of the experimental application of permethrin would be gauged. The Village of North Haven, north of Sag Harbor, was also used as a control area, as the deer population there had been reduced beginning in the late 1990s by nuisance hunters. The results of the experiment, which was concluded at the end of 2010, were recently published and made available on the Internet.
Tick densities were not the only factor examined. The relationship of the four-posters to deer collisions on nearby roads was also studied, as was the impact on vegetation in control and treated areas. Permethrin is a powerful insecticide, so the amount of it found on harvested deer necks was swabbed. Deer movements were recorded with G.P.S. collars fitted on several deer. In order for the experiment to be faithfully carried out, the roller applicators at each four-poster had to be regularly charged with permethrin.
The number of deer visits was measured both by photography and the amount of bait, in this case corn, taken in a given year. Thousands of pounds of corn were consumed, some of which was found in the stomachs (the rumens) of deer that were harvested during the special shotgun hunting season in January and by bow and nuisance hunters. Raccoons, which are not widely known as tick vectors, visited the four-posters as frequently as deer, and even squirrels and birds came regularly. The three different mammals using the sites all received permethrin hits.
It was a very meticulously contrived and carried out experiment and the results were not unexpected. The resulting tick densities as measured by 30-second flaggings in random locations throughout the control and treated areas told the story. Throughout the course of the experiment, deer numbers and deer sizes increased, perhaps due to the availability of corn in the four-posters, but also because of good acorn years as measured in the Nature Conservancy’s Mashomack Preserve on the island.
In the treated areas, tick populations dropped considerably, especially for the Lone Star tick, which was the most frequently observed both on Shelter Island and Fire Island. In the last year of the experiment, both species of ticks had been decreased in the treated areas vis-a-vis the control areas, the Lone Star tick more significantly so. In 2010 there were comparatively low numbers of deer ticks in all of the sites tested, including North Haven.
Vegetation was eaten both at the control sites and the treated sites, with the maximum damage being more profound at the control sites. There was no significant correlation between deer-vehicle collisions and proximity of four-poster stations over the course of the study.
Permethrin exposure was the most worrisome thing. Swabs from the necks of harvested deer showed significant amounts of permethrin and on some harvested deer permethrin was found in the neck muscle immediately below the hide attachment. Livers, spleens, and other body organs may have cached some permethrin over time, but none was detectable in tests conducted by the New York State Health Department.
Short of killing deer and thus removing the primary hosts for deer and Lone Star ticks altogether, the use of the four-posters, while requiring regular maintenance, renourishment, and occasional replacement, did decrease the tick population in the area in which each was deployed.