Last week I argued that focusing on deer rather than mice is the best way to reduce the number of ticks and tick-borne illnesses on Martha’s Vineyard. This week I want to discuss three techniques for reducing the number of deer and/or ticks:

• Using four-posters to apply an acaricide (permethrin) to deer, killing the ticks on the deer.

• Using birth control or sterilization to limit reproduction and reduce the number of deer over time.

• Reducing the number of deer directly by increased hunting.

Unfortunately there is no silver bullet. None of these methods are easy or quick, and given the diversity of opinions on the Vineyard, all three are bound to be controversial. However, it is clear to me that without first reducing the number of deer on the Island, birth control, sterilization, and deploying four-poster feeding stations will be difficult and extremely expensive. I expect the most fruitful and politically acceptable approach will be a combination of two or more of these methods.

Four posters have a bin filled with corn; when the deer eat the corn, rollers apply permethrin to their heads, necks and foreparts. One advantage of four-posters is that they kill all types of ticks and have been shown to reduce the density of both lone star and deer ticks.

Four posters also have their drawbacks. One is that you cannot purchase or operate one without a permit from the Massachusetts Division of Fisheries and Wildlife (DFW). Currently DFW is only issuing permits for research purposes. Four posters were field tested on the Vineyard a few years ago; however, DFW has not issued any new permits since that research ended.

A second issue is that many hunters do not like four-posters because they put permethrin on the deer, which they fear may present a health hazard.

Third, other animals such as crows, squirrels and raccoons also eat the corn from four-posters. This has the potential to not only artificially increase numbers of these species but to concentrate them in areas around the four-posters, including near-rare species, such as piping plovers and terns.

However, probably the most serious drawback is the cost. The Vineyard research indicated that four-posters must be deployed at the recommended density of one for every 120 acres of habitat to be effective. The Vineyard is approximately 64,000 acres. To properly treat even the 10 per cent of the Vineyard with the highest densities of lone star or deer ticks would require 53 four posters. Although the initial cost is only about $400 to $700 per four-poster, annual costs to operate them can be substantial. In addition to the cost of purchasing corn and permethrin, someone needs to refill the corn on a weekly basis and a certified pesticide applicator is required to refill the permethrin twice a month.

I found two estimates for annual operating costs. In Fairfax County, Va., it cost about $47,000 per year to maintain 20 four-posters, or about $2350.00 per four-poster. Estimated costs for Easthampton, N.Y., were $4500 per year per four-poster. (I assume much of the disparity was due to employee wages; in Fairfax county wages were $15 per hour while in Easthampton labor costs are probably more similar to the Vineyard.)

Even if we use the lower annual cost, maintaining 50 four-posters would cost over $100,000 per year to cover 10 per cent of the Island. The estimated cost of maintaining the 250 four-posters needed to cover half the Island would be between $587,500 and $1.125 million.

Both birth control and sterilization have been tried in a number of places, with mixed results. In the past 25 years, both techniques have been refined and it now seems that they can reduce the number of deer in a closed system, such as an Island, where new deer don’t move in to replace those that die. The shortcomings of both methods are the relatively long time frame (about 10 years) before there is a significant impact on population size, the number of deer that have to be treated (between 70 and 90 per cent of females) and the cost. Most studies recommend the use of birth control to maintain the population only after the deer herd is at the desired size.

The New York Department of Environmental Conservation concluded that “fertility programs are the most expensive option for deer population control due to the costs of manpower and materials and the level of effort needed to treat an adequate number of deer.” The Indiana Division of Fisheries and Wildlife concluded that “the high cost, short-term effectiveness, need for boosters, timing of the application, and the impracticality of treating an adequate number of deer, severely reduce the practical use of birth control agents for free ranging deer.”

In older studies, birth control costs have been reported as $300 per doe; however more recent figures tend to be around $1,000 per doe. Assuming half the estimated 3,000 deer on Martha’s Vineyard are female, between 1,050 (70 per cent) and 1,350 (90 per cent) of the does would have to be treated, at a cost that would likely exceed $ 1 million. In addition, the effects of existing birth control methods are temporary and boosters have to be administered annually. Even though subsequent years are less expensive, this still greatly increases the costs over time.

Sterilization (generally by removing ovaries) has also been tried. The problems are similar to those with contraception. Costs are high, generally reported as about $1,000 to $1,200 per doe, and 70 to 90 per cent of the does in a population must be sterilized for the technique to be effective. Again, assuming 1,500 females, this means between 1,050 to 1,350 does would have to be sterilized. At $1,000 each, the initial cost would exceed $ 1 million, and although the cost should be lower in subsequent years, it would still be substantial.

While non-lethal methods of deer and tick control such as four-posters, birth control and sterilization have their appeal, I firmly believe the only practical and affordable way to reduce the number of deer and ticks on Martha’s Vineyard is through increased hunting. I also believe it is time to change the discussion from the different ways to reduce deer and ticks to how we can support and encourage hunters to take more deer. Although several steps have already been taken, including adding a second week of shotgun season, allowing hunters to take more does and making it easier to get multiple doe tags, we need to do more. We are asking more private landowners to open their land to hunting as well as helping them find responsible hunters when they do.

There are also some adjustments to the hunting seasons that should help reduce deer ticks. The peak in adult deer tick activity is mid to late October through early November. By late November, when shotgun season starts, most female deer ticks have fed, mated and dropped off to lay eggs. Taking more deer in October and early November, either by increased archery hunting or an earlier shotgun season, would reduce feeding opportunities for female deer ticks and the number of eggs. Adding an additional week of shotgun season in January is would also help reduce the number of deer.

Thank you for taking the time to read these articles. I hope you will join us in a productive and civil discussion and then help us take the actions needed to end the epidemic of tick-borne illnesses on Martha’s Vineyard.

Richard Johnson is a longtime Island biologist who leads the tick-borne illness prevention program for the Martha’s Vineyard Boards of Health.