White-tailed deer (Odocoileus virginianus) are one of the most easily recognized wildlife species in New Jersey. Highly valued as a major game species, white-tailed deer are increasingly perceived as nuisance animals because of their negative interactions with humans, particularly in densely populated areas. Agricultural crop destruction, private property damage, deer-vehicle collisions, and tick-borne illnesses are all important points to consider in the management of deer. Deer also offer amenity and economic value for hunting and ecological benefits (i.e., seed dispersal, increased plant diversity) when they occur at appropriate densities. A full understanding of deer populations will help us to manage them effectively.
The New Jersey Division of Fish and Wildlife (NJDFW) has designated 61 management zones in the state, based in part on land use, geography, habitat type, and biological factors. Deer within each zone are treated as an individual population, with each zone having different management objectives. There are also 15 special deer management areas, which include military bases, national wildlife refuges, and county and state parks, with added flexibility in management to meet specific deer management goals. Delineation of management zones can be found at state.nj.us/dep/fgw/images/hunting/deer_zone_map.jpg, and state.nj.us/dep/fgw/pdf/deerzones.pdf (PDF).
Biology of the White-Tailed Deer in New Jersey
White-tailed deer are large mammals generally ranging in size from 50-200 lbs. While some adult males (bucks) can grow up to 3.5 ft tall at shoulder height and weigh up to 200 lbs, an average buck in New Jersey weighs around 150 lbs. Females (does) are typically smaller and average around 100 pounds. Their summer coats are reddish-brown and gradually fade to a brownish-grey in the winter. Deer under the age of 1 yr (fawns) are 4-8 lbs at birth and have red coats with white spots, which help to conceal them from predators (Figure 1). As young deer grow their first winter coat, the white spots disappear. In April, bucks begin growing their antlers, which are covered in a “velvet” layer of skin, consisting of soft hairs and blood vessels that provide nutrients to the growing tissue. Bucks then rub off this soft layer once their antlers are fully grown. The size of these antlers is determined by age and nutrition levels. Antlers are shed annually each winter.
Does generally reach sexual maturity at 2 years of age. However, reproductive potential is directly related to nutritional state, so with good resources, fawns as young as 6 months can begin breeding. This phenomenon is common in New Jersey. Younger animals and new mothers usually produce one fawn, with twins becoming more common in yearling does; triplet litters may occur in older does. Deer breed from late September through January, with the peak of breeding (rutting) activity occurring in mid-November. Fawns are born beginning in early May.
White-tailed deer are herbivorous browsers, feeding on virtually every part of many different plant species. Foraging mostly in the dawn and dusk hours, deer will eat approximately 2 to 7 lbs per 100 lbs of body weight each day. As edge species, deer are commonly found where forested habitats abut more open areas, such as shrublands, agricultural fields, and riparian zones. Deer are also commonly found in suburbs, the ideal edge habitat, where appropriate resources are highly abundant. Studies by the NJDFW have determined the average home range size to be around 1 square mile, and even smaller in resource-rich agricultural and suburban areas.
Why Are Deer Overpopulated?
By the late 1800s, the deer population in the northeastern U.S. was at a critical low due to overharvesting. However, the deer population quickly rebounded following restocking efforts and the enactment of several protective measures, such as game laws and seasonal hunting restrictions. The deer population experienced further population growth during the early 20th century due to the combined effects of several factors. Agricultural and horticultural practices created a constant supply of high quality food resources for deer. Extirpation of natural predators, such as wolves (Canis lupus) and cougars (Felis concolor), lowered natural mortality rates. Reductions in recreational hunting further reduced deer mortality; in areas where hunting continued to persist, hunter preferences for antlered bucks favored female survival and ultimately population growth. Because New Jersey’s landscape is highly developed, hunter access to deer is limited due to safety regulations.
Ecological Impacts
At appropriate densities, deer help to maintain biodiversity in ecosystems. By feeding on dominant plants within the habitat, deer open up space and resources for less competitive plants, allowing them to gain a foothold in the vegetative community. In this way, moderate browsing balances the ecosystem and increases plant diversity. However, as deer increase in abundance, browsing pressure reaches a tipping point, where individual plants cannot recover from the damage. Plant abundance and diversity decline rapidly, leading to several cascading negative impacts on the ecosystem.
By feeding on or damaging tree seedlings and saplings, an overabundant deer population prevents forests from naturally regenerating. The shrub and herbaceous layers also disappear, leaving a barren woodlot of trees rather than a healthy, functioning forest (Figure 2). With significantly less vegetation than a healthy forest, other ecosystem processes are impacted. The lack of leaves falling to the ground each autumn results in poor quality soils, increased erosion, and a lack of nutrients required for plant growth and reproduction. These changes, combined with the openness of the forest floor, make room for nonnative plant species to colonize, further compromising the health of native habitats.
Habitat changes caused by overbrowsing are also detrimental to native birds, small mammals, and invertebrates. Many birds nest in native vegetation on or close to the forest floor, while others rely on the constant supply of insects within the leaf litter and in vegetation to feed themselves and their young. The absence of nuts and berries in overbrowsed forests also leads to a decrease in food supply for small mammals and migratory birds, making it difficult for them to survive at critical times during the year.
Impacts on Human Health & Safety
Tick-Borne Diseases
Increases in tick-borne illnesses are often attributed to deer overabundance because deer serve as hosts for many tick species, particularly the deer tick (Ixodes scapularis). The most common disease associated with deer ticks is Lyme, which is caused by the bacteria, Borrelia burgdorferi, and categorized by a recurrent arthritis and an annular rash. Although the increasing occurrence of Lyme disease in the northeast is attributed to deer overabundance, mounting evidence suggests that increases in the abundance of small mammal hosts are actually driving Lyme disease risk. Other tick-borne illnesses include babesiosis, human granulocytic ehrlichiosis, and human monocytic ehrlichiosis, which all cause flu-like symptoms. These diseases are all treatable, with early detection improving treatment results.
Deer-Vehicle Collisions
Between July 1, 2010 and June 30, 2011, there were over 1 million deer-related collisions in the U.S. From 2011-2012, more than 31,192 deer-vehicle collisions occurred in New Jersey alone, making the likelihood of hitting a deer 1 in 191. Although the frequency of deer-vehicle collisions is largely influenced by human population size, road density, deer density, time of year, habitat, road type, and speed limit, defensive driving behavior has been shown to minimize accident risk. Deer are most active seasonally from mid-September through November during the peak of the breeding season (rut). Activity increases shortly after sunrise and between sunset and midnight. Deer crossings commonly occur where roads cause fragmentation of intact forest or separate forest from agricultural lands. Heightened driver awareness in these areas during peak activity periods can help reduce deer-vehicle collisions. Obeying the speed limit and using high-beam headlights can also increase driver reaction time.
Agricultural Damage
Wildlife damage to U.S. agriculture is reported to result in the loss of $4.5 billion of crops annually. White-tailed deer are responsible for the majority of the damage. A 1998 survey specifically targeting New Jersey farmers revealed that deer are responsible for 79% of wildlife-related agricultural damage, resulting in a yield loss of $5-10 million per year. Deer damage occurs in the form of feeding, buck rubs, and/or trampling of crops and is characterized by a torn, jagged appearance on vegetation or a square, ragged break on woody material. Most browse damage occurs from the ground level up to a height of approximately 6 feet. Residual damage may occur from the trampling or matting down of vegetation as deer travel through crop fields or bed down to rest. Buck rub damage, which occurs as males shed the velvet from their antlers each autumn, can be identified as scarred saplings, broken limbs, bruised bark, and/or exposed wood. Rubs usually are located on the trunks of trees up to 3 ft above ground level.
Most producers in New Jersey have become intolerant of high deer densities and the associated damage to crops. The 1998 survey indicated that over a third of New Jersey farmers forgo cultivation of preferred crops due to excessive deer damage. Normal crop rotation is also hindered, and 25% of the time New Jersey farmers will abandon a field completely. Crops that experience the most damage from deer include grains, corn, soybeans, pumpkins , tomatoes, and lettuce.
Several challenges exist in the management of deer on farms. Due to increased development, many New Jersey farms are located within 1 mile of residential developments or protected lands where hunting is prohibited. These areas become refuges for deer, leading to further increases in herd size. In addition, although farmers may apply for permits to shoot (PTS) through the NJDFW, many rent their land and cannot secure hunting rights from the landowner. On farms where hunting is permissible, many farmers allow recreational hunters access to the land.
Management Strategies
Depending on policy regulations, public perception, individual preferences, and efficacy, an effective deer management strategy may incorporate several components from a suite of alternatives. The following section provides a brief description of common deer management strategies. Non-lethal methods may minimize negative deer impacts over short time intervals, while lethal methods offer more long-term solutions to the problem of locally overabundant deer. For more information on New Jersey’s deer management program, visit www.njfishandwildlife.com.
Lethal Methods
Sport hunting is considered the most cost-effective, efficient method of deer management. To increase hunter yields, NJDFW introduced the taking of antlerless deer, known as “doe days” as early as 1933 in areas where crop depredation was a serious problem. The deer hunting season has expanded significantly since then, opening the second Saturday in September and closing the third Saturday in February every year. Two-thirds of the state has unlimited antlerless bag limits. Hunters have been successful in reducing deer densities where they have access to hunting lands; however, the lack of hunter access continues to be a severe obstacle to successful deer management in the most densely populated state in the nation.
Land managers in deer management zones with more restrictive hunting regulations may apply for a Deer Management Assistance Permit (DMAP), which allows for the take of additional antlerless deer in order to meet management goals. In areas where sport hunting is not practical, municipalities, counties, county boards of agriculture, and airports may apply for a Community Based Deer Management Permit (CBDMP), which allows for lethal methods not permitted under sport hunting regulations. Additionally, all deer meat not utilized by the control agents must be donated to the Community Food Bank of NJ.
The CBDMP program allows sharp-shooting by specially trained professionals, an effective culling method that can be used in areas with excessive deer numbers and that are too developed for a traditional hunting program. Hired sharp shooters can operate at night using spotlights and silencers. In contrast to sport hunting regulations, permits for sharp shooters can be awarded outside the legal hunting season, and there are no bag limits. However, this strategy can cost municipalities approximately $200-$500 per deer.
Euthanization of individual deer with a captive bolt gun is also allowed under a CBDMP. A captive bolt gun is a mechanical device used in commercial meat slaughtering operations to dispatch the animals. Although controversial, this method is accepted conditionally by the American Veterinary Medical Association. This method also is labor intensive and more expensive than other management strategies.
Non-Lethal Methods
Chemical Fertility Control
Chemical fertility control includes contraceptives, which are given to female deer to disrupt reproductive behaviors, or contragestational drugs which cause spontaneous abortion in pregnant deer. Only specially trained wildlife professionals with a permit are able to administer this treatment. However, reductions in population size may not be noticeable for 5-10 years as deer die off. This strategy is labor-intensive and costly, and because individuals consistently move into and out of a population, treating a threshold level of individuals is not guaranteed. In addition, there is currently no available contraceptive with a 100% efficacy rate; therefore, deer populations will continue to increase under this strategy. At this time, contraceptives are not a practical approach to deer management; however, research is ongoing. If fertility control for deer becomes cost-effective and efficient in the future, lethal methods will likely be required to first reduce the population to acceptable levels where it can then be maintained chemically.
Trap and Relocation
Deer relocation programs have been attempted at small scales to reduce local herd sizes. However, this strategy is labor-intensive, costly, and impractical at large scales. Studies on deer trapping have shown that up to a 21% mortality rate may occur. Relocating deer does not reduce the population; rather, it transports the problem to a new area. The spread of diseases, such as chronic wasting disease (CWD), is also a concern; therefore, the relocation of deer is banned by many states.
Exclusion
Several alternative physical barriers exist to protect ecosystems, crops, and residential landscaping. Individual plants can be protected with flexible netting or wire caging, and tree seedlings can be covered with plastic tubes (tree shelters). Although labor-intensive, protecting individual plants has been shown to be successful in many situations. However, use of tree shelters may inadvertently increase mortality of songbirds, such as bluebirds, which enter the tube chasing an insect and ultimately get caught inside. Flexible netting or some other device to block entrance to the tubes should be employed.
To exclude deer from larger areas, several types of fencing exist. High-tensile woven wire (HTWW) fences are very effective at moderate to high levels of deer when installed correctly. These fences consist of a series of smooth wires placed 9 inches apart on top of 6.5 ft of woven wire fencing to a total height of 8-10 ft. HTWW fences are durable and long-lived, providing maximum cost-effectiveness. Portable electric fencing is another alternative with documented effectiveness in areas up to 25×50 ft in size. When first installed, deer should be lured to electric fences with an attractant (i.e. peanut butter) so they develop an association between the fence and a negative consequence. This type of conditioning must be continually reinforced to produce maximum effectiveness. Cloth strips and reflectors should also be placed on the fence to increase visibility. Detailed information on the planning and installation of HTWW and portable electric fences can be found on the Rutgers NJAES website.
Repellents
For small-scale gardens and flowerbeds, taste-based or odor-based repellents can be effective at discouraging deer. Only certain commercial products are approved for use on garden vegetables or fruit trees. Common repellent ingredients include urine from a natural predator, such as coyote or bobcat; hot sauce derived from capsaicin in pepper; and putrescent eggs. Attractiveness and palatability of the plants, deer hunger, amount of rainfall, and local food preference are among factors influencing repellent effectiveness. To maximize success, repellents should be used with additional deer management tactics in an integrated approach.
References
- Cote, S.D., T.P. Rooney, J. Tremblay, C. Dussault, and D.M. Waller. 2004. Ecological impacts of deer overabundance. Annual Review of Ecology, Evolution, and Systematics 35:113-47.
- Drake, D. 2000. A private lands approach to controlling New Jersey’s deer population. Wildlife Damage Management Conferences – Proceedings. Paper 28.
- Levi, T., A.M. Kilpatrick, M. Mangel, and C.C. Wilmers. 2012. Deer, predators, and the emergence of Lyme disease. Proceedings of the National Academy of Sciences 109(27):10942-10947.
- NJ Division of Fish and Wildlife. 2000. Community Based Deer Management Manual for Municipalities. New Jersey Department of Environmental Protection. state.nj.us/dep/fgw/pdf/cbdmp_manual.pdf (PDF).
- Rutgers Cooperative Extension. 1998. How are white-tailed deer affecting agriculture in New Jersey? Survey findings briefing report & maps. October 7, 1998. snyderfarm.rutgers.edu/DeerFAQ/_pdf/Brief%20Summary%20Deer%20Rpt.pdf (PDF).
- Seagle, S.W. and J.D. Close. 1995. Modeling white-tailed Odocoileus virginianus population control by contraception. Biological Conservation 76:87-91.
- State Farm Mutual Automobile Insurance Company. 2012. Likelihood of collision with deer (2011-2012). statefarm.com/aboutus/_pressreleases/2012/october/24/likelihood-of-collision-2012.pdf (PDF).
January 2013
