ROCKY MOUNTAIN NATIONAL PARK, Colo. (AP) -- As dusk falls, an eerie, high-pitched squeal pierces the stillness of the alpine meadow.
It is the sound of love for majestic bull elk, which beat their antlers on the ground, wallow in mud and occasionally clash horns in fierce battles to win the affections of cow elk.
Throughout the fall, dozens of tourists shake off the evening's chill and click cameras, enthralled by the spectacle in the meadow in Rocky Mountain National Park.
''You're privileged that they let you into their territory,'' said Gwen Quick of Greeley, as she, her husband, her son and daughter-in-law watched the elk on a recent evening.
Mary Lou Swinburne of Ponce Inlet, Fla., sat in a lawn chair, recording the scene on a video camera so she could share it with her grandchildren. Her husband, Bruce, watched through binoculars as a bull elk slowly began picking off females, or cows, by herding them up and bugling.
The elk mating season draws hundreds of tourists to Rocky Mountain National Park every fall.
The elk also wander into nearby Estes Park, ambling along its main street, nibbling trees and back yard gardens and creating unusual obstacles at the Estes Park Golf Club course.
''I just like seeing them wander around,'' said Bob McFarland, who recently played the course as a herd of elk grazed on the grass and a bull elk watched from under the shade of a tree.
''Between the elk and the tourists, it's pretty hard to run a golf course,'' said course manager Jack McDade.
The elk are descendants of 49 elk transplanted from Yellowstone National Park in 1913 and 1914 after the area's original herd died out because of overhunting.
In 1915, the 358-square-mile park was created, offering vistas of 14,000-foot and higher peaks, alpine tundra and wildlife.
Today, there are about 3,400 elk living in the Estes Valley, with about 1,000 wintering in the park, said park management biologist Therese Johnson. The number of elk outside the park has been growing by 6 percent a year.
The park has about 3.4 million visitors every year, and is increasingly popular in the fall.
To accommodate the crowds, park officials offer educational seminars and an all-volunteer group, called the Bugle Corps, helps direct traffic and keep visitors a safe distance from the animals.
The mating season begins when the weather cools and the days grow shorter in the fall. Mature bulls, from 8 years to 9 years old, attempt to attract groups of cows, called harems, by polishing their antlers, urinating on themselves and wallowing in mud to attract the opposite sex.
Sometimes, they destroy a bush and drape the branches over their antlers to make them appear bigger, said Dave Lensink of Grand Rapids, Mich., a park interpretative intern.
The competition begins with the bugling sound, followed by occasional clashes. The bulls also stay up most of the night to keep an eye on their cows, which leaves them little time to eat. Bulls lose an average of 100 pounds during mating season.
Occasionally, a mature elk will steal a harem while two younger males battle, said Lensink.
On a recent night, a group of about 40 elk gathered in the meadow near one of the park entrances. Parked cars lined both sides of the road and volunteers with batons helped direct the traffic and answer questions.
The volunteers also occasionally stopped cars to allow herds of elk to cross the road.
The Swinburnes have come seven nights in a row, sharing coffee from a thermos until it's too dark to see the elk.
''It's almost impossible to come in to the park without seeing one,'' said Bruce Swinburne.
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