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White-tailed Deer Immunocontraception in Irondequoit New York
Contraception and Deer: The Irondequoit Report
by William
Porter and Brian Underwood
- Abstract
- Order the Report (PDF)
Irondequoit, a suburb of Rochester, New York, is one of many communities across the US where white-tailed deer (Odocoileus virginianus) populations have grown dramatically over the past 30 years. The suburban landscape is composed largely of residential neighborhoods and parks that provide deer with ideal habitat. Many suburban residents enjoy seeing deer and consider deer to be an asset to their community. However, as deer populations have grown, so have conflicts with humans. Automobile collisions, browsing of ornamental plants, and concerns about Lyme disease are on the rise. Local governments are faced with the dilemma of whether or not deer abundance should be actively controlled, and, if so, how control should be implemented.
We sought to examine the feasibility of using immunocontraception to manage a free-ranging population of deer. Specifically, our objectives were to identify factors that would determine the effort required to deliver contraceptive treatments via dart rifle in a suburban environment where deer could move about without restriction. We measured the relationships among these factors as a first step toward an eventual experiment with population management and associated cost analysis. We attempted to determine the minimum population size that could maintained through immunocontraception. Actually controlling growth of the deer population and measuring efficacy of the treatment were beyond the scope of this project.
The Town
Irondequoit is a suburb of Rochester, New York. The town is 17 square miles in size. About 8 square miles is commercial development and supports few deer. The remainder of the town is residential with large yards and parks and numerous wooded ravines. The Town is bounded by the Genesee River to the west and Irondequoit Bay to the east, neither of which present barriers to movement of deer. To the north is Lake Ontario and to the south is the city of Rochester.
The Deer
In 1995 there was an estimated 16.7 deer/km2. Between 1992-1995 there were 688 deer killed by automobiles.In 1993 a bait-and-shoot operation was initiated and 844 deer have been culled between 1993-2000.
Contraception
Contraception in wildlife is challenging because dosage and timing of delivery is often critical for the drug to work effectively. Daily dosage is impossible to accomplish in free-ranging wildlife populations. Further, synthetic hormones like the Pill can be passed along the food chain, affecting animals that consume a treated deer. Immunocontraception is a creative alternative to the Pill that circumvents both of these problems.
The word, immunocontraception, is a combination
of the words immuno, as in immunological, and contraception. As
the word implies, immunocontraception operates
through the immune system. Immunocontraception stimulates the body
to produce antibodies against the proteins produced by the reproductive
system. Immunocontraception involves injecting a chemical (in this
case, a protein) into the body. One protein now being used is Porcine
Zona Pellucida, or PZP. Zona pellucida is a scientific name for
the protein membrane that occurs on the outside of all mammalian
eggs.
Biologists obtain the protein from eggs in the ovaries of pigs, hence the name, Porcine Zona Pellucida. When we introduce this protein into the body of a deer, the immune system begins to produce antibodies that recognize and attack the Zona Pellucida protein. Therefore, when the deer's own ovary releases an egg, the antibodies mistake the deer Zona Pellucida as a foreign protein and attack the egg, preventing conception.
Experience with PZP shows that two shots are required
in the first year and at least one shot, annually, thereafter. To
reach the high levels of antibodies necessary to prevent fertilization,
PZP must be combined with an adjuvant. An adjuvant is a chemical
compound that causes exceptional stimulation of the immune system.
To deliver PZP to deer, we create a vaccine by combining the PZP
with the adjuvant, and 
load the mixture into a dart. The dart contains
a syringe and hypodermic needle that inject the vaccine. We shoot
the dart from a specially-designed
rifle into the large muscle mass of the hip of the deer. The dart
contains a small charge of gunpowder that explodes when the dart
hits the deer. The charge pushes the plunger of the syringe, injecting
the drug. The dart then falls out and is recovered by the biologist.
Although the effects of PZP are well understood, use of PZP is regulated by the US Food and Drug Administration (FDA). PZP is considered to be an experimental drug and all application to free-ranging deer must occur under license of the Food and Drug Administration. The license agreement requires that all free-ranging animals treated with PZP be clearly marked with identifying tags before treatments can be administered. Following initial capture for marking, treatments may be delivered remotely with a dart gun.
Irondequoit was the first study of contraception (in this case PZP) in an environment typical of most suburban communities facing the dilemmas of deer management. At the outset of the study no one had direct experience with using contraception to control growth in a free-ranging deer population. Earlier work at Front Royale had focused on behavioral impacts of contraception. Other trials at Fire Island were not applicable because of the unique nature of the deer population and the geography of the island. Still other studies at the National Institute of Standards and Technology, and in Connecticut were focused on small populations in environments with excellent access to deer. No one had attempted to deal with a population numbering hundreds of deer in an environment ranging from flat, grassy backyards to rugged, wooded ravines.
The field study conducted in Irondequoit was one
component of a larger cooperative study commissioned by the New
York State Legislature. With leadership provided by the New York
Department of Environmental Conservation, scientists from the State
University of New York College of Environmental Science and Forestry
at Syracuse, and the College of Agriculture and Life Sciences at
Cornell University undertook a four-year investigation. The intent
of the overall study was to provide the people of New York with
a comprehensive assessment of contraception as technique for managing
deer populations in parks and surburban environments.
Findings
Population densities were estimated from helicopter counts conducted during late winter. Physical condition, including pregnancy rate, was determined from deer removed during ongoing culling operations. Effort to deliver treatment via dart rifle was measured during initial capture operations, and during delivery of booster shots of vaccine. Each deer that was captured was fitted with a radiotransmitter collar to enable monitoring of movements and survival.
Contraception can be used to control deer populations.
Our studies in Irondequoit show that the immunocontraceptive vaccine,
Porcine Zona Pallucida (PZP), can be effectively delivered via dart
rifle in this suburban environment. However, controlling deer population growth
town-wide with immunocontraception will present a challenge for
three reasons: (1) a significant portion of the population is wary
and reclusive, (2) not all land in the town is accessible for purposes
of darting deer, and (3) there are biological limits on the size
of the population that can be effectively managed with contraception.
The best potential for contraception as a management technique will
be for applications on a small geographic scale such as parks or
neighborhoods.
Encounter rates for darting deer depend on deer density, approachability, and land access. The time required to locate, approach and deliver a dart is highly variable. The assumption that all deer are equally approachable and all land areas are accessible is simplistic and rarely true. Deer are harder to locate when densities are low, and some deer are hard to locate regardless of density. Other deer are frequently seen, but are wary of human approach to within darting range. If a significant portion of the female population is difficult to approach or difficult to dart, then time invested in delivering treatment to the necessary number of females will be high. Investments increase further if thick vegetation and rugged terrain make darting difficult, or if access to lands where deer spend most of their time is limited by landowner or safety concerns.
Effort per deer increases as more deer are treated.
Experience dictates that some deer are less visible and more difficult
to approach than others. Some individuals are seen frequently, respond
to bait, and are easily approached, while others are more wary.
Deer that are frequently seen and easily approached tend to be treated
first. As more deer are treated, those that remain to be treated
comprise a pool of individuals whose behavior makes them increasingly
difficult to approach at close range. In a strict sense, no deer
in the town are so wary as to be ultimately untreatable, but effort
will be high. We confirmed this effect in Irondequoit and measured
the accelerating rate of investment needed for each deer that is
treated. Qualified people darting deer in the community for several
years would increase the efficiency of this process through learning
the land and the deer. However, deer also learn from darting and
many would become increasingly wary. How these opposing learning
experiences would change the time invested in management is unknown.
Effort will be greater if populations are reduced
via culling. At low densities, the effects of culling on density
and approachability are likely to interact, exacerbating the problem
of encountering deer. The time invested to treat deer will be greater
if populations are reduced to low densities via culling because
the remaining deer will be those that are best able to avoid being
shot and, therefore, the most wary. At higher densities, modest
reductions or reduction activities that are limited to only a portion of the town may have
less impact on darting effort. Such culling would not selectively
remove all of the easily darted animals and the pool could be large
enough that treating wary individuals might not be necessary.
Radiocollars can reduce effort and may pay for
themselves through decreased personnel time. Placing radiocollars
on a sample of deer and using the radiocollars to make decisions
about where and when to attempt to dart deer can reduce effort.
The value of radiocollars is likely to be greatest with low-density
populations. With large populations, radiocollars are unnecessary
because finding sufficient numbers of deer is relatively easy. 
With
low populations, radiocollars seeded among sparse pockets of deer
can serve to locate groups of animals, thereby enhancing the rate
of encounter by reducing the time invested in searching for deer.
The initial cost of collars seems high: $200 to 250 each, replaced
every two to three years because of limits of battery life. However,
these costs may be trivial in comparison to the savings in personnel
time.
The minimum population size that can be maintained by contraception alone is about 25% of ecological carrying capacity. Controlling growth in a population is ultimately dependent on treating sufficient numbers of sexually mature females to ensure that births do not exceed deaths each year. If the efficacy of treatment is 100%, then the limit on the size of the population that can be maintained is zero. With a treatment efficacy of 90%, the minimum realistic management goal for population abundance is about 25% of ecological carrying capacity (K). The limit is imposed by the interaction between the proportion of females in the population and the efficacy of treatment. Efficacy rates that exceed 90% are questionable under field conditions.
Effort is likely to limit our ability to manage populations at low density. A possible solution to the challenge of achieving high efficacy is to continue darting the same females until it is certain that all received a complete injection. When numbers of deer to treat are small and there are many field crews darting, such an approach would be possible. This approach could yield near-100% efficacy. However, at low densities, nearly every breeding female will need to be treated, and investment in effort will be high.
To maximize cost efficiency, deer management should
occur at a neighborhood scale. The most workable situation may be
to consider applying contraception to a subset of the town-wide
population. Such an approach would be workable if the movement behavior
of 
deer
is such that density in a given area could be reduced and not be
swamped by deer moving in from higher densities on the surrounding
landscape. Behavioral data suggest that deer in Irondequiot establish
small home ranges and use these consistently from one year to the
next. Such fidelity to a home range has been shown to occur in other
environments, and studies have shown that localized reductions in
density do not result in any shifts in movement of deer from immediately
surrounding landscapes. Effort is reduced by focusing on neighborhoods
because fewer deer need to be treated and the technique can be applied
selectively in areas where conditions are most suited to darting.
We recommend application of contraceptive treatments through a process of adaptive management. Our study lays the foundation for a direct test of the idea that abundance in free-ranging deer populations can be controlled using contraception. We have learned which factors that are critical to estimating costs, provided preliminary measurement of those factors, and determined the limits to biological feasibility of the technique. The next step in the development of this technique should be a full-scale test of a contraceptive program to control population growth over a period of at least five to ten years. We recommend that such a test be conducted in an experimental fashion with an intent of eliminating the uncertainties in three areas: the ability to achieve efficacy rates of greater than 90%, the changes to expect in encounter rates as both people and deer learn about darting, and the potential to control local populations apart from surrounding populations.
About The Author:
Dawn Gorham
Ph.D. candidate: Relationship of Deer Overabundance to Landscape M.S. in Veterinary Science, 1997, University of Wisconsin, Madison B.S. in Biology, 1995, State University of New York at Buffalo
I am currently examining landscape characteristics of a number of suburban neighborhoods with the goal of determining which characteristics are associated with deer overabundance and conflict. This information can then be used in community planning to determine how landscapes might be better designed to minimize deer-human conflict.
Contacts and Links
William F. Porter
SUNY-ESF
1 Forestry Drive
Syracuse, New York 13210
website
Deer Info:
- DEC - New York's Deer Management Program
- USGS - Annotated Bibliography of Methodologies to Census, Estimate, and Monitor the Size of White-Tailed Deer (Odocoileus virginianus) Populations
- National Park Service - Management of White-tailed Deer in National Parks
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