The Three-Minute Outdoorsman: Wild Science from Magnetic Deer to Mumbling Carp

4. Urban Deer

A L L T H I N G S D E E R 23 early detection system for the disease in captive deer make CWD a potentially critical issue throughout the range of deer in North America. 4 urban deer hunting versus birth control Many urban deer herds are at all-time high population levels. In many areas, wildlife agencies issue unlimited permits for antlerless deer. From a biological perspective, when there are too many mouths to feed, less food goes in each, so individual birth rates fall, and death rates rise. When these factors balance, individuals on average leave one offspring, and in the jargon of ecologists, we say that the population is at its carrying capacity and is relatively stable. In the suburbs, we tend to plant stuff that deer like to eat, and we remove big predators. These actions tend to increase deer abundance. Human reactions to this new higher equilibrium number of deer depend on whether people enjoy seeing deer or just had the front end of a new vehicle replaced. In the Twin Cities metropolitan area and others, the question arises as to how to control high deer numbers. One method is a liberal hunting opportunity. Some urban parks that are normally closed to hunting conduct permitted bow hunts or hire sharpshooters to kill deer. The former option provides opportunities for many hunters that might not otherwise be able to hunt. However, the antihunting public sometimes reacts negatively to hunting virtually in their backyards. How to deal with large numbers of deer is becoming an important issue as suburbs expand and encroach on more and more land, putting humans and deer in greater and greater conflict. The use of contraceptives is another method to reduce deer. t h e t h r e e - m i n u t e o u t d o o r s m a n 24 The public often favors this means of herd reduction because it reduces birth rates and is viewed as more “humane.” I, like probably a lot of others, responded to questions about whether we can manage high-density deer herds with contraceptives by saying it doesn’t work. However, I have to admit that I gave this response based on hearsay. So, when a scientific review of contraceptive use in wild animals appeared, I took a crash course. What follows is a summary of a paper in the journal Integrative Zoology by Kathleen Fagerstone of the U.S. Department of Agriculture and colleagues. These authors review the ways in which contraceptives can be used to limit deer numbers. Two main methods are to administer a chemical contraceptive via food (orally) or directly via injections or implants. Each has its advantages and disadvantages. Oral contraceptives are easy to distribute but generally considered ineffective or impractical for deer because the deer must consume them regularly, plus other organisms might ingest them with unintended detrimental effects. Several contraceptives have been injected. One category includes steroid hormones, which have been shown to reduce or inhibit estrous behavior in does. Although this method inhibits reproduction in whitetails (by interfering with ovulation or implantation in does and by impairing sperm production in bucks), it requires continuous doses from an implant or frequent injections. Thus, because their effects are short-term, steroids are not currently considered a viable contraceptive. A second class of chemical contraceptives is “immunocontraception vaccines.” These cause an animal to produce antibodies against their own reproductive proteins and can last from one to four years. The vaccine SpayVac, for example, has been effective in preventing reproduction in does for up to four years after a single shot, an advantage over many others that require annual booster shots (and like many people, deer lack health insurance). Although it prevents pregnancy, SpayVac can make does have multiple or back-to-back estrous cycles and thereby extend the potential “breeding” season. A different study evaluated the possibility that A L L T H I N G S D E E R 25 this would cause increased deer-vehicle collisions, because bucks would be chasing does across highways for an extended rut period, but the researchers found no evidence for it. SpayVac is not currently used to manage whitetails in the United States. Another vaccine is GonaCon Immunocontraceptive Vaccine . A single injection reduces or eliminates reproduction in both sexes of white-tailed deer. In bucks, the vaccine reduces testosterone levels...