In the Crosshairs
What happens when a national park has too many deer?
After a torrential morning rain in late May, the sun is blazing and the air is steamy, making the luxuriant beech and oak forest canopy pop against the basically bare ground. “It looks like someone came through here with a lawnmower,” says Ken Ferebee, natural resource management specialist with the National Park Service.
We’re walking off trail—no bushwacking required—in the northern portion of Rock Creek Park, a 1,750-acre scenic oasis that starts in Maryland and runs along the creek through Washington, D.C., all the way to the Potomac River. It’s one of the country’s oldest and largest urban parks, managed to remain as wild as possible. In the backyard of the National Zoo and hundreds of houses and apartment buildings, the park is a recreation spot for bikers and picnickers, and rugged enough for hikers and even horseback riders.
In the past two decades, it has also become a delicatessen for deer, with trees, shrubs, and wildflowers on the menu. Deer munch shoots and leaves almost as fast as they come out of the ground, leaving no chance for the understory—layers of vegetation, including seedlings, saplings, and youngish trees about 15 to 20 feet tall—to develop, says Ferebee. When a big tree falls, nothing is growing up behind it to take its place, and the sun streams into the big hole left in the canopy, allowing the spread of invasive plants that deer tend to avoid.
Once nearly extinct in the eastern United States because of commercial hunting and habitat-gobbling development, white-tailed deer numbers were down to about 350,000 nationwide at the end of the 19th century. States began enacting laws to protect them in the early 1900s, but it took decades to bring the population back. Today deer have very few predators in the East; humans long ago wiped out wolves and mountain lions, and hunting is also off limits in ever-expanding suburbs and exurbs—where the fragmentation of green space mirrors the open foraging areas and surrounding thick forest cover that deer prefer.
The result: a burgeoning U.S. deer population that has returned to its historical numbers of 25 million to 40 million. And that is burdening national parks and battlefields in the East, many of which have turned to sharpshooters to cull the numbers each year. Rock Creek, with more than 300 deer within park boundaries, is one of the latest. Others—including Catoctin, Gettysburg, Manassas, and Valley Forge—are developing proposals or have plans in effect. “We’ve never needed to kill animals in the park before,” says Ferebee. “But now the deer are having such an impact, it requires intervention.”
Not unexpectedly, the move has upset those who prefer birth control over bullets. They want deer to live out their normal lifespans in places where hunting is off limits. Sometimes they sue to prevent the cull.
This happened most recently to Rock Creek Park when a handful of private D.C. citizens, and In Defense of Animals, a national animal-protection nonprofit, filed a lawsuit in 2012. They alleged that the Park Service is cherry-picking its science, and that the park’s plan is inhumane and unnecessary because successful reproductive control exists.
“We love both the deer and the national park, but the decision to kill the deer has affected the public’s ability to enjoy the park and has ruined the Park Service’s reputation here,” says Carol Grunewald, a plaintiff whose property is near the park. “Our scientists show that Rock Creek Park can easily support 300 deer. But regardless of the numbers, the public will no longer stand for the routine, mass extermination of animals.”
Their legal petition included a scientific analysis by Oswald Schmitz, a professor at Yale’s School of Forestry and Environmental Studies, stating that deer don’t have an adverse impact on the park’s vegetation because forests are self-thinning. That is, seedlings compete for sunlight and other resources, most die, and in the end, a thousand seedlings in an area, for example, may produce only 20 trees with or without deer present.
Their action delayed the park’s cull by a year, but ultimately a court dismissed the case on the grounds that Congress granted the Park Service the authority to act in Rock Creek Park’s interest.
Although not a plaintiff in the lawsuit, the Humane Society of the United States (HSUS) also criticized the park’s plan during the public comment period, championing the nonlethal solution of using a fertility-control vaccine on the herd as an alternative.
“We think Rock Creek’s plan is a wasteful killing program and a lost opportunity to repress the growth rate,” says Stephanie Boyles Griffin, senior director of innovative wildlife management and services at HSUS. The group offered to pay 50 percent of the cost of sterilizing the park’s deer. “We asked park officials to give fertility control a chance, to show they had explored and exhausted all methods before resorting to lethal control,” she says. “The problem wasn’t created overnight, so why does it have to be solved overnight?”
An approach that combines sharpshooting with reproductive control from the start would work best, argues Boyles Griffin. “Sadly, more often than not, the government goes for lethal methods,” she says. “With fertility control—although expensive at first—the costs get less and less. If you’re just killing deer year after year, the does you don’t kill have fawns and you have to increase the death toll the next year to get to your numbers.”
National parks including Rock Creek and Valley Forge have the option of using reproductive control in their deer management plans, providing fertility methods meet certain criteria. Ferebee says he’d like to have a cost-effective “magic bullet”—actually a magic dart—that delivers an infertility drug to does that lasts up to five years.
Recent breakthroughs after decades of research include a contraceptive called PZP. Its most recent formulation, still in the experimental stage, works for two to three years. PZP first proved effective in the field with wild horses at Assateague Island National Seashore in Maryland and later, with deer at Fire Island National Seashore in New York.
But contraception has its challenges. Once darted, deer grow warier, and they get harder to hit in subsequent years. Dart guns also fire at lower velocities, and the much-heavier darts travel slower than bullets, requiring a person to get within 20 to 30 yards.
Fertility control might work in the future, Ferebee says, but with 77 deer per square mile, a number that is static but too high, the park needs to control over-browsing immediately.
Biologists involved in Rock Creek’s federally required Environmental Impact Statement, designed to assess options and their environmental effects, concluded that 15 to 20 deer per square mile is a more suitable number if the goal is to keep the forest healthy and regenerating. “It’s not that we’re against reproductive control,” Ferebee says. “First we have to get it down to the target number. It doesn’t matter if we have 10 deer or a thousand deer,” he says. “What matters is getting the plants back.”
It’s not uncommon for deer to live eight to 10 years in parks with no hunting. Without the stress of pregnancy, birth, and nursing, they might live even longer. “We could give birth control to every female, but it might take five or six years for the population to change,” he says. “This tactic is really not practical to reduce the population in a short time.”
That’s the reason Valley Forge National Park in Pennsylvania began culling in 2009. The park is now down to 50 deer per square mile from a whopping 240 deer per square mile five years ago. In those years, long-missing ash, black gum, cherry, hickory, maple, oak, and sassafras seedlings returned, along with wildflowers not seen for 20 years.
“There was no doubt something needed to be done,” says Deirdre Gibson, chief of planning and resource management at Valley Forge. “The environment was being lost. We had such severe over-browsing there was nothing left but old trees and exotic plants that deer don’t prefer.”
And so, on six winter nights this year in Rock Creek, two professional sharpshooters from Wildlife Services, a federal agency within the Department of Agriculture, used bait stations, night-vision equipment, noise-suppression devices, and small-caliber rifles to spot and kill 69 females and 37 males in closed areas of the park. The park donated thousands of pounds of venison to a local food bank for the homeless.
Ferebee compares this to a recent undertaking by Fairfax City, Virginia, where officials hired a private company to use nonlethal control. They captured only 16 does for sterilization over six nights. “We, on the other hand, shot 98 deer in six nights, and those deer are gone,” he says. “They are not going to be here munching away.”
I get a window into what a more sustainable Rock Creek would look like when Ferebee and I arrive at one of the 16 vegetation plots spread throughout the park. The patches were fenced in 2000 to serve as controls to see what grows where deer can’t graze.
Inside the 3-foot by 12-foot plot, it’s green, lush, and blooming. Ferebee points out spicebush and maple leaf viburnum—native shrubs—along with May apples and beech, black cherry, and red maple seedlings. Outside the fenced area, in one of 27 open control plots, hardly anything is growing anywhere. The groundcover is mostly just last season’s fallen leaves from the mature trees overhead.
Ferebee does manage to find some Virginia creeper, two little maples, and some sprouts from the roots of a black gum tree. “I don’t want to imply there is nothing,” he says, “but those won’t last to summer.”
When groundcover disappears, not just deer but all the park’s wildlife—which includes foxes, opossums, beavers, flying squirrels, box turtles, and salamanders, along with 181 bird species—feels the effects. Ground-nesters like oven birds and wood thrushes lose out, and predators get an unfair advantage. Mice, voles, and shrews become easy pickings for owls and other birds of prey.
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Allowing deer to destroy the habitat for all the other animals in the parks is unacceptable, say national park managers. Over-browsing also leads to severe erosion, particularly now that climate change is causing more intense storms. “Given all the damage done over the decades, it’s hard to know when things will come back,” says Valley Forge’s Gibson. “We can’t step back to how things were before deer made the land so bare. Today, the climate is much hotter, rain is more acidified, and rainstorms are more hurricane-like, which intensifies erosion. We’re in a brave new world as far as forest regeneration.”
To see a much bigger example of healthy vegetation, Ferebee takes me over to Carter Barron Amphitheatre, Rock Creek’s summer stage for Shakespeare in the Park, the National Symphony Orchestra, and other events. The gate is kept closed on about five wooded acres—fenced since the 1950s—except on event nights. Deer don’t often enter. When Ferebee slides the iron bars closed behind us, I can’t help but think of Dorothy entering the Technicolor world of Oz. The landscape goes from sparse to jungle-like in an instant. It’s hard to argue that deer, in excessive numbers, don’t have a destructive effect.
As we walk through the multilayered understory, Ferebee points out plants—including garlic mustard, an invasive he plucks as he identifies it—and tells me how deer weren’t an issue anywhere in the park until about 2000. The park’s visitor observation cards from the 1960s record only four deer that entire decade. In fact, Rock Creek staff set up the vegetation plots in 1991 when deer numbers were low partly to see how a park with low deer density looked against a park with high density.
Now, these plots will determine the course of deer management. “If we find we don’t need to take many animals next year, we will adjust our plan,” Ferebee says. “The green in the plots will tell us. It’s really black and white there.”
About the author
HEIDI RIDGLEY writes about history, travel, and wildlife conservation from Washington, D.C.