White-tailed deer, North America’s most abundant larger herbivore, number an estimated 30 to 35 million in the United States, found in every state but Alaska, California, Hawaii, Nevada and Utah. With hunting restrictions, their population has rebounded to where it was before Europeans arrived. Adaptable, deer evolved in forests and meadows but thrive in human-shaped habitats—the edges of roadways and forests, parks, suburban yards. Often, as woods and open space is developed, they are forced into close contact with people.
Deer can be frustrating for gardeners not used to sharing their flowers and plants with another species. Their increased presence can make people anxious about vehicle collisions or Lyme disease. But with knowledge and compassion, people can adapt to the arrival of deer in their neighborhoods and communities. In most cases, deer are actually returning to the forests and fields, now developed, that they inhabited centuries before. Only now, many more people have moved in and predators such as mountain lions and wolves are missing.
You can minimize damage to gardens with readily available solutions. Under mild browsing conditions, repellents may be all you need. You might combine them with scare devices. Under heavy browsing conditions, you may need to limit your plants to the more deer-resistant varieties (ask your local Cooperative Extension Service) and use deer-proof fencing around your garden. Deer are curious and motivated by their need to eat, so they may test and retest the barriers and deterrents you use. Stay a step ahead of them by changing what you apply so they don't get accustomed to any one strategy.
A variety of repellent products used singly or in combination, can repel deer. Commercial repellents work by creating unpleasant tastes or odors, gastrointestinal discomfort or a sense of pain (hot pepper or peppermint).
Some of the more effective repellents contain a sulphurous odor (e.g., rotten eggs) believed to induce fear because deer associate it with rotten meat or a predator. Some examples of popular repellents include Liquid Fence and Deer Away® Big Game Repellent, which both consistently score high in studies assessing effectiveness. Visit a local garden, farm supply or hardware store and ask which repellent work best in your area. Predator urine products are not effective and should never be used because they come from fur farms, which raise wild animals in small cages and kill them for their pelts.
Tips for applying repellents
- All repellents work best if applied before the deer's feeding pattern becomes established. Apply them before bud-break and as new growth appears.
- Reapply repellents after heavy rains and at least every two to three weeks.
- Deer may become accustomed to the same repellent, so alternate repellents to keep the deer confused and warier. At the height of growing season, use an odor repellent over a taste-based one. Taste-based repellents need to be constantly applied to any new growth to keep the whole plant tasting bad.
- Hang bars of soap high in fatty acid (e.g., Irish Spring brand) on trees or shrubs you want to protect.
The key to using scare devices is to couple them with other strategies like repellents, varying the kind used and changing their location in your garden.
- The Scarecrow Motion-Activated Sprinkler attaches to a garden hose. When a deer comes into its adjustable, motion-detecting range, a sharp burst of water is sprayed at the animal. The combination of physical sensation and a startle effect provide effective aversive conditioning.
- The Havahart Spray-Away Elite Motion Detector is similar in action to the Scarecrow, yet is hose-free and solar powered. This device uses infra-red technology to detect animal movement
- The Havahart 5250 Electronic Deer Repellent consists of 3 stake-like devices and a scent lure. Deer are attracted to the lure and then receive a mild electric shock when they reach it.
- The Deer Shield Electronic Deer Guard is a device which emits varied digital recordings of alarmed and territorial deer, thereby using their own form of communication to inspire deer to go elsewhere.
Where deer browsing is a serious problem, the only effective way to protect crops or plants is with fencing. There are a variety of fencing options ranging from eight-foot woven wire fencing, to electric fence garden kits, to poly-tape (electrified nylon) fences, which are portable and good for temporary use. The best type depends on how large an area you need to protect and for how long, so check with your local garden store or local Cooperative Extension agents before buying anything. The eight-foot-high woven wire fence stands out as the most effective deer barrier and lasts more than 20 years. However, when deer are really hungry, they will jump fences eight feet or even higher.
Electric fences can deter deer well. They provide a "psychological barrier"—deer can jump over them, but they learn to avoid electric shock. Such fences can be constructed in a variety of configurations and are powered by high-voltage, low-amperage chargers that provide timed pulses of short duration. They must be maintained with regular voltage checks and mowing so that overgrowth doesn't short out the lower wires.
To ensure that deer learn their lesson, some electric fences have a scented bait attachment which entices the deer to make contact with the fence—after which they receive a mild jolt to their nose or tongue. Aluminum foil squares containing a dab of peanut butter can provide the same "enhancement" when folded over single or multi-strand electric fences.
Hardware cloth (wire mesh), corrugated plastic, chicken wire and netting
"Buck rubs" are the damaged areas created by bucks rubbing against trees to remove the velvet from their antlers. Prevent buck rubs by wrapping trees with any commercial product sold for that purpose, or by placing cylinders of hardware cloth or corrugated plastic sleeves around the trunks.
To prevent browsing on young saplings until they reach a height of four to five feet, use small-scale, temporary fencing enclosures or individual tree "shelters" (hardware cloth or corrugated plastic). You can drape mesh netting over low-growing plants or vegetables that are likely to get eaten, but because birds might get caught in the netting, it’s better to use chicken wire or hardware cloth.
No matter how big or small your outdoor space, you can create a haven for local wildlife. By providing basic needs like water, food and shelter, you can make a difference in your own backyard.
Deer are scapegoats for larger ecological problems of biodiversity loss and forest-growth failures. Notions of overpopulation, or how many deer are too many for a given area, are subjective. It may be true that deer densities are at historic highs, but the forests of today in no way represent historical conditions. Urbanization has created an abundance of edge habitat, which is ideal for browsing deer. Deer have simply adjusted their populations to available resources.
Are deer damaging forests?
It is easy to blame deer for problems with forest growth, but these many other factors contribute to these: Acid rain, insects, disease, forest fragmentation, pollution, loss of soil fertility, browsing by other animals, invasive plant species, parasitic organisms, climatic and weather extremes and development. Forest growth in deer "exclosures" (small areas fenced to exclude deer is often pointed to as proof of deer impacts on forests, yet we must be mindful that these protected areas show us what a patch of forest might look like without any deer. Such a state is no more "natural" than deer presence in great numbers.
Are deer causing biodiversity loss?
We may want to see more biodiversity in certain areas because we saw it there in the past. Yet nature is not static; a forest floor carpeted with wild flowers can rapidly transition to another state as a result of forest succession. Certain plant species are shaded out as trees mature and the forest canopy closes. Later successional stages are, by their very nature, less diverse. We shouldn’t blame deer for every change. Consider these research findings:
- Trillium is often used as an indicator of high deer abundance. Yet studies have shown that soil acidity, not large numbers of deer, may more strongly influence where purple trillium and other wildflowers will grow.
- A Yale Forestry School study of 120 study plots in six Connecticut towns across western Connecticut found that deer density is not a leading factor in tree regeneration decline or loss of plant diversity.
- Deer hunting can have unintended negative consequences for populations of snakes, salamanders, amphibians and many invertebrates.
Are deer harming songbirds?
Deer browsing can alter bird-nesting habitat. But many other factors are directly harming native songbirds, including the destruction of over-wintering habitat in South America, the broad-spectrum use of pesticides, pollution, the clearing and development of deciduous forests, plate-glass windows, weather extremes and diseases like West Nile Virus. Surprisingly, new evidence suggests that some songbirds, like robins and other thrushes, actually prefer to nest in invasive shrubs such as honeysuckle and buckthorn that have moved in because of deer browsing. The shrubs provide protection for the birds from predators.
Sometimes communities respond to deer conflicts with killing programs to reduce deer “overpopulation,” to protect trees, shrubs and gardens, and to prevent vehicle collisions and Lyme disease. These usually don’t work. There’s no correlation between deer densities and the number of deer conflicts. A comprehensive approach using non-lethal methods will be most effective in reducing. Communities should study the problem. They shouldn’t assume there are too many deer. People and deer can peacefully coexist.
Deer kills do not keep deer numbers down
Deer are prolific. They respond to declines in their populations by reproducing more quickly. Remaining female deer will often react to greater food abundance by giving birth to twins or triplets. With more to eat, fawns also have higher survival rates and reach sexual maturity sooner. The end result is a "bounce-back" in numbers.
To be successful, a killing program must not only significantly reduce the deer herd, it must sustain enough pressure to prevent this bounce-back effect, while also preventing deer from the surrounding area from wandering in. All of this usually poses an insurmountable challenge in urban and suburban communities.
In addition, it isn't safe to hunt in most suburban areas where deer are causing conflicts, because there are too many people. It's no surprise that many suburban deer kills—no matter what target level is set—end up killing very few deer, after which the population quickly returns to its previous level.
Killing deer will not protect gardens and shrubbery
Certain plants like tulips and hostas are irresistible to deer. Even if the deer population could be greatly reduced, these favorite flowers would still be eaten by any remaining deer. Effective solutions focus on deterring deer and protecting flowers and ornamentals by “deer-proofing.” Choose plants deer generally don’t like, such as daffodils and irises, boxwood and pachysandra. The key to success is for residents to understand that deer are here to stay.
Killing deer will not stop deer/car accidents
Studies have shown that reducing the deer population does not necessarily reduce the number of collisions between cars and deer. In some cases, collision numbers are lower in areas with more deer. Many factors contribute to deer-vehicle collisions, such as traffic volume, speed limits, the extent to which roads bisect habitats and migration routes and the use of visual barriers. Killing deer will not solve the underlying problem, which is that we have trapped these animals within a network of highways crisscrossing their territory and have failed to construct wildlife underpasses or overpasses that allow safe crossings. Deer-aware drivers can avoid collisions.
Deer kills will not reduce the incidence of Lyme disease
Scientific studies have shown killing deer won't reduce people's risk of contracting Lyme disease. Deer kills do not significantly reduce the population of the tick that spreads the disease—the black-legged tick (or deer tick), which feeds on almost all mammals, most songbirds and even lizards. In Great Island, Mass., when up to 70% of the deer were removed, there was no marked reduction in tick abundance. Where deer are scarce, ticks switch to other hosts or congregate in higher numbers on the remaining deer. The most effective ways of reducing the risk of Lyme disease are to avoid tick bites and to use products like Damminix Tick Tubes and 4-poster tick control devices to reduce the tick population.
Wildlife fertility control offers a humane way to manage deer populations. Researchers have developed methods of deer “birth control”—ways to keep deer from reproducing. The Humane Society of the United States has focused on one of them: PZP (porcine zona pellucida), an immunocontraception vaccine that can keep adult female deer from becoming pregnant and has reduced deer populations by as much as half. Surgical sterilization or ovariectomy is another option for humanely controlling deer population growth. Although it is expensive, it need only be done one time. Removing the ovaries or a large enough percentage of an area’s does has been shown to reduce deer populations by as much as 45%.
PZP works by causing an immune reaction in does that blocks sperm fertilizing eggs. Unlike some fertility control vaccines and methods that cause undesirable behavior changes, PZP simply prevents fertilization. Most importantly, because PZP is a natural protein, like all other proteins found in animals, it is safe to use and will not harm animals. PZP can be delivered to adult female deer by hand or remotely using darts shot from a dart gun.
Recent improvements in the PZP vaccine now prevent deer from having fawns for up to three years with just one treatment. This significantly reduces the time needed to dart animals and so the costs of treating deer.
Since the 1990s, the HSUS has conducted several successful PZP immunocontraception research projects on deer. Here are the four biggest:
- Fire Island National Seashore (FINS) was the HSUS's original deer study site. The primary goals there were to see whether more than 200 deer could be darted each year and to the effectiveness of PZP on what had been a growing deer population. The deer were easily darted and the immunocontraceptive alone was shown to reduce a deer population over time.
- The HSUS also used PZP over a period of 20 years to treat the deer on the fenced campus of the National Institute of Standards and Technology (NIST) in Gaithersburg, Md. The number of deer collisions dramatically decreased, the remaining deer became healthier and the deer population growth rate fell, despite the fact that urbanization and development around the facility caused constant migration of new deer onto the campus.
- Over a five-year period of darting deer on Fripp Island, S.C., with PZP, the deer population decreased by nearly 60 %. In addition, the remaining deer were healthier. Residents were pleased and the number of human deer conflicts fell.
- An eight-year study in the New York City suburb of Hastings on Hudson, N.Y., showed that PZP could reduce a deer population in an area that was not bounded by water or by a fence by as much as 50 %. The terrain in Hastings on Hudson was challenging, with close together homes and rocky hills, but researchers managed to dart more than 60 percent of the does. The treated does stayed in their territories and kept new, untreated does from moving in. The study showed that two shots given over a period of two and half years can prevent fertilization for up to five years.