Darts offer non-lethal population control

 

While no one has invented a birth-control pill for does, and fitting a buck with a condom would be a hazardous activity, some say contraception is a viable means for controlling a population of urban deer.

Critics of the method believe birth-control vaccines — delivered with a dart gun — are costly, inefficient and perhaps dangerous to human health, but in a recent interview a wildlife contraception expert said those arguments don’t stand up to hard evidence.

“It matters not to me whether people use this or not ... the only thing that gets my back up is when somebody says this doesn’t work,” said Science and Conservation Center Director Jay Kirkpatrick, a life-long hunter. “It does work, and it works well.”

The center, a nonprofit organization located at Zoo Montana in Billings, makes the porcine zona pellucida vaccine, or PZP, used worldwide to control populations of deer, horses, elephants and other mammals.

The vaccine, derived from pig eggs, distorts the membrane surrounding mammalian eggs, closing the gate on fertilizing sperm.

The method has been used to control deer herds at the Fire Island National Seashore, a 32-mile barrier isle off the coast of Long Island, N.Y., and at the National Institute of Standards and Technology in Gaithersburg, Md.

Kirkpatrick’s staff helped set up a lab in South Africa, now making enough PZP to dart 1,000 elephants a year. The situation there is similar to the urban deer management discussions taking place in this country, he said.

“Half the public says, ‘Hell, shoot them,’ ... and the other half says ‘No, they’re a national treasure,’” he said. “It’s pretty much the same.”

Darted animals need to be inoculated every year to prevent pregnancy.

Populations are reduced through natural mortality, once reproduction has been halted.

The method isn’t intended for large geographic areas and works best in “small, discreet urban populations,” Kirkpatrick said.

The National Institute of Standards and Technology is located on a sprawling 578-acre campus in Maryland, surrounded by a 10-foot fence.

In the mid-1990s, the agency’s land was home to more than 300 whitetail deer, spokesman Michael Newman said, resulting in deer-vehicle collisions — and the occasional rutting buck crashing through a window after seeing his reflection.

“We looked at a lot of different (management) options,” Newman said.

Safety concerns at the 24-hour facility, along with public opinion in surrounding neighborhoods, prompted officials to rule out hunting.

The Humane Society of the United States, which coordinates projects using the PZP vaccine, offered to work with the facility and officials jumped at the chance, Newman said.

The herd now numbers about 175 deer, he said.

“For us, it works particularly well,” he said. “It does allow us to successfully manage the deer population. It doesn’t affect the behavior of the deer.”

Newman said he’s unsure whether the vaccine would be as successful elsewhere.

Security concerns limit the campus to one controlled-access gate, and areas where hills enable the deer to jump the fence are scarce.

Most of the deer inside the fence stay in, and it’s likely few make it in from the outside.

A migratory barrier — in this case, water — also limits the coming and going of deer on Fire Island, said Michael Bilecki, resources management chief at the national park.

“The fact that it’s an island ... is significant for us,” he said. “I can’t speak to how something like this would work on the mainland.”

But Kirkpatrick said the surrounding waters are a moot point.

Whitetail deer remain in the same half-square-mile range their entire lives, he said, ruling out migration as a factor.

He said mule deer venture farther, but all of his projects have involved whitetails.

On the 32-mile-long island, located east of New York City, the vaccine has been a success over the past decade, Bilecki said.

PZP has been used to manage deer populations in the 15 or so communities that dot the island’s west end.

“We’ve seen populations decrease and then, in some areas, populations have leveled out,” he said.

“In some areas — and we can’t figure out why — we’ve seen little bumps in the population going up,” he added.

On the Web:

www.pzpinfo.org

Larry Kline can be reached at 447-4075 or [email protected].

From pigs to deer

In all mammals, a membrane known as the zona pellucida surrounds each of the female’s eggs.

The barrier includes molecular keyholes, which allow sperm from the same species in to fertilize the egg.

The porcine zona pellucida vaccine, or PZP, is derived from pig eggs. When it’s injected, it stimulates the female’s body to produce antibodies, which distort her eggs’ openings.

“Now a sperm comes along, and its little molecular keys won’t fit the little molecular keyholes,” researcher Jay Kirkpatrick said. “It’s kind of like changing the tumblers in a lock.”