Three white-tailed deer stole the show at a Pennsylvania horse race last week, beating the horses to the track and dashing around wildly under the lights (see video above).

"As they race down the track, Bambi has the lead!" veteran race caller Roger Huston exclaimed over the PA system, narrating the animals' frantic romp up and down Meadows Racetrack in Washington, Pa. "Here comes Rudolph from the outside!"

The trio seemed fast enough to challenge any thoroughbred, but as Huston noted, their performance was hindered by frequent directional changes. The show ended when they wandered off the track toward the infield, according to KDKA-TV.

This counts as good publicity for a sport that often makes news by spurring controversies and losing fans. But it's also relevant beyond horse racing, since the sight of deer bumbling into civilization has become all too familiar across North America. The Eastern U.S. is especially overpopulated with white-tailed deer, thanks to generations of ecological mismanagement that removed predators, promoted prey and fragmented forests with things like highways, houses and horse tracks.

Americans increasingly clash with all kinds of wildlife, from grizzly bears in Alaska to alligators in Florida. This is largely due to a mix of conservation success and failure, since people have helped animals rebound while building over their old habitat. It may also stem from "species partisans," a term used by author Jim Sterba in his new book "Nature Wars: The Incredible Story of How Wildlife Comebacks Turned Backyards into Battlegrounds." As Sterba explains, such people arbitrarily favor some species over others, with preferences often driven more by cuteness than ecology.

White-tailed deer epitomize this effect. Rampant hunting made them rare in the Eastern U.S. 100 years ago, but gray wolves were also being shot, trapped and poisoned into oblivion. The latter eventually disappeared from the Lower 48 states, nearly joined by other predators such as cougars, bears, gators and crocodiles. And while this caused little public outcry, the decline of white-tailed deer did. As wildlife ecologist Bill McShea told NPR in 2011, state wildlife agencies rushed to the rescue, banning or limiting deer hunts in hopes of boosting their numbers.

"They went and got deer from Arkansas and brought them here to repopulate that area," said McShea, who works with the Smithsonian Conservation Biology Institute in Virginia. "So growing the deer population was intentional. It's a conservation story and it went just like they planned. And now the flip side has happened."

With no wolves or cougars to keep them in check, white-tailed deer took over. Wiser conservation policies later helped some predators rebound in some areas, but the U.S. white-tailed deer population has nonetheless ballooned to about 30 million, and under ideal conditions it may double every two years. The species can reach densities of 250 per square mile, with each deer eating up to 1,000 pounds of vegetation annually.

white-tailed deer

Photo: U.S. National Park Service

This leads many herds to overgraze their native foods, altering forest growth by eating swaths of saplings and other young plants. With fewer new trees to replace dying elders, entire ecosystems can grind to a halt, robbing native wildlife of shelter and food while creating an opening for invasive species. "The future is not good," McShea says of deer-heavy forests. "There's no teenagers here. There's no young adults."

On top of devouring their own ecosystems, hordes of deer can also be an immediate danger both to humans and themselves. It may be funny when they race on a horse track or crash into a Taco Mac, and a bit more annoying when they eat an entire Christmas tree farm. But it becomes a matter of life and death when they try to cross roads and highways, which they often do at night when visibility is low.

West Virginia has the nation's highest deer-car collision rate, according to data compiled by State Farm, with one in 40 licensed drivers striking a deer every year. The top overall state is Pennsylvania, which had more than 115,000 collisions between July 2011 and June 2012. Such encounters are often fatal to deer, but can also injure and kill people inside the cars, especially when drivers swerve into trees or other vehicles. According to State Farm, the national number of deer strikes has increased 7.7 percent since 2011, while the average cost of repairing damage is now $3,305, up 4.4 percent.

Hunters may put a dent in some deer populations; in West Virginia, they killed 60,000 bucks last year, a 38 percent spike from 2010. But the state is home to 800,000 white-tailed deer, up from a low of about 1,000 in 1910. Many larger states have more than a million, including Michigan (1.7 million), Mississippi (1.7 million) and Texas (4 million). According to a 2011 report on state deer numbers, "the overall national picture for whitetail populations ... is good to very good almost across the board."

Without natural constraints from full-time predators like wolves and cougars, that picture seems unlikely to change anytime soon — making Bambi and Rudolph potential dark-horse picks for anyone feeling lucky at the Meadows Racetrack this Christmas.

Related deer and horse stories on MNN:

MNN tease photos of deer and track: Shutterstock

Russell McLendon ( @russmclendon ) writes about humans and other wildlife.

Deer invade horse track, start racing [Video]
The speedy trio entertained fans and announcers, but they also highlighted the real problem of deer overpopulation in ecosystems across the Eastern U.S.