Americans' love of hiking has driven elk to the brink, scientists say

Trail use near Vail, Colorado, has more than doubled since 2009. It's had a devastating impact on a herd of elk

Biologists used to count over 1,000 head of elk from the air near Vail, Colorado. The majestic brown animals, a symbol of the American west, dotted hundreds of square miles of slopes and valleys.

But when researchers flew the same area in February for an annual elk count, they saw only 53.