As two scientists with extensive experience using fertility treatments to control wildlife populations, we want to set the record straight regarding whether the National Park Service needs to begin killing the white-tailed deer that live in Rock Creek Park — a small patch of nature in our nation’s capital. Our analysis of the data convinces us that any such measures to reduce the deer population in this park would be premature and unnecessary.
To begin with, the Park Service’s own data do not show a deer population crisis. According to the agency, deer numbers have fluctuated between 50 and 90 deer per square mile since 2000; higher densities can be found in places in Maryland and Virginia. But more to the point, the Park Service’s data show that Rock Creek’s deer population has remained stable for 10 years, and some densities in recent years are actually below those of earlier years. As the Park Service also acknowledges, the telltale sign of a serious deer overpopulation problem — a “browse line” indicating that deer have eaten most of the vegetation within their reach — has not been detected in the park. The deer themselves are in good condition. They are not starving.
But even if there were a problem in this park, there are far more humane — and effective — ways to control urban deer populations than killing, which can increase reproductive success within the remaining herd and create room for deer from neighboring areas to move into. As the authors of many peer-reviewed scientific studies on this issue, we know that fertility control is, over the long term, a more effective and publicly acceptable way to deal with urban deer problems. One fertility-control vaccine, porcine zona pellucida (PZP) — which can be administered by shooting the animal with a dart — is safe for deer and for predators, scavengers and any humans who happen to consume venison from a treated deer; it is a natural protein that degrades in the deer’s body after injection, and if eaten, it is destroyed in digestion.
The Park Service is quite familiar with PZP (which the Science and Conservation Center manufactures and makes available at or below cost for noncommercial wildlife and zoo research and wild-horse management applications). This vaccine has already been used effectively to help tackle wildlife management challenges on at least four Park Service properties. PZP has reduced urban white-tailed deer numbers at Fire Island National Seashore in New York; controlled wild horse populations at Assateague Island National Seashore in Maryland and Cape Lookout National Seashore in North Carolina; and slowed growth of the Tule elk population at Point Reyes National Seashore in California. And it has been used since 1994 to limit white-tailed deer conflicts at the National Institute of Standards and Technology (NIST) in Gaithersburg.
The more recently developed contraceptive agent GonaCon — which can last for several years — has been approved by the Environmental Protection Agency for use in free-roaming deer. Although it must be administered to the animal by hand, this is no more labor-intensive (and certainly is more humane) than lethal control by trapping deer and killing them with a bolt gun, which is built into the Park Service’s reduction plan (which also calls for shooting deer with guns and arrows).
There is no reason to believe that the successful use of fertility control at NIST, Fire Island and elsewhere could not be duplicated in Rock Creek Park. On the other hand, if the Park Service starts killing deer immediately to reduce the population, it will make the humane approach of fertility control that much harder in the future. These deer — which have never been hunted in the 120-year history of this park — will become fearful of humans once the shooting begins, making it much more difficult to approach deer closely. In fact, we know of no published reports describing control of an urban deer population by shooting animals first and then administering contraceptives later. Yet this is currently the plan for Rock Creek Park.
While the National Park Service may want to take more immediate action for a range of political reasons, we see no legitimate scientific justification for resorting to lethal control of this closely observed urban deer population. Neither do we see any reason why fertility control could not be attempted to gradually reduce the deer in Rock Creek Park to address any perceived overpopulation.
Having worked closely with the Park Service for many years on similar wildlife problems, we find it painfully ironic that the same agency that for so long occupied the leading edge of nonlethal wildlife control should resist such a prudent and logical application. Because of its location in the heart of our nation’s capital, Rock Creek Park “serves as an ambassador for the national park idea,” in the words of the Park Service itself. That ideal should encompass humane wildlife management.
The writers are, respectively, director of the Science and Conservation Center in Billings, Mont., and director of the Center for Animals and Public Policy at the Tufts-Cummings School of Veterinary Medicine.