The changing natural world at our doorsteps | Illustration and text by Patterson Clark
April 9, 2013
Deer problems, contentious solutions
Until mountain lions and timber wolves return to the District, Rock Creek Park’s swollen deer herd
will have to depend on humans to control its numbers.
Too many deer lead to a decline in biological diversity, an increase in invasive vegetation and a loss of the seedlings that would naturally replace old trees when they fall. Controlled hunting of deer is the quickest and least expensive way to regenerate a forest, but some advocate managing the deer population with birth-control injections.
In the late ’90s, the National Park Service began a deer-reduction program at Gettysburg to restore the battlefield's historic woodlot and improve forest regeneration. After 11 years, the park reached the desired deer density of 25 per square mile. Seedlings and saplings are now surviving to become trees.
Having weathered a legal challenge, a similar program for Rock Creek Park is underway. The park's deer density was about 73 per square mile at last count. Target density: 15-20 per square mile.
Although deer culling in the park is currently done only with lethal methods, the Park Service continues to examine birth-control options. A birth-contol agent, however, must meet several criteria. It must . . .
♦ be federally approved,
♦ prove successful for 3 to 5 years,
♦ be administered by dart,
♦ leave no residue in the meat,
♦ have little or no behavioral impact on the deer.
"No agent exists at present that fully meets all criteria," said Nick Bartolomeo, the park's chief of resources management.
The Humane Society of the United States, which strongly opposes what it calls Rock Creek Park's "wasteful killing program," has offered to pay half the cost of a pilot project that would use PZP, a fertility-control vaccine. Recently developed time-release pellets might provide birth control for at least a couple of years. Injected into a captured deer or carried by a dart, PZP causes antibodies to bind to a deer's eggs, blocking fertilization.
"Similar immunocontraception programs have been successfully used in multiple trials to reduce deer and wild horse populations, including in public-private partnerships between the National Park Service and the HSUS on Fire Island, N.Y., and Assateague Island, Md.," Stephanie Boyles Griffin, a wildlife scientist with the HSUS, said in an e-mail.
The Park Service reviewed the HSUS proposal and the 15-year research project on Fire Island. "We determined that HSUS's immunocontraceptive
- Forest in balance
- Too many deer
- Gap dynamics
A mix of predators and deer leads to a high level of biodiversity.
Enough seedlings develop into saplings to regenerate the forest.
Deer prefer eating native vegetation, giving invasive plants an advantage.
Many tree seedlings vanish. Birds nesting in understory trees disappear.
When a large tree falls, a gap in the forest canopy allows sunlight to flood
onto the forest floor. Invasive plants quickly overwhelm saplings.
Without population control, the deer herd suffers from malnutrition. Oak, hickory
and beech trees eventually disappear, replaced by the few species that deer avoid.
agent would not act quickly enough to reduce the deer population and therefore would not protect Rock Creek Park's forest and other resources," Bartolomeo said.
Another problem with PZP is that it extends a deer's breeding season, which could add extra energy demands and even yield births late in the season, "leading to higher fawn mortality as winter ensues," says the park's plan.
Bartolomeo said that such artificial and potentially deleterious effects would fundamentally conflict with Park Service policies, which require management strategies that work within the scope of natural processes. Although they roamed the park many years ago, "large predators wouldn't be tolerated if they were here," Bartolomeo said, "so we have to take this action."