It's a threat to wildlife that isn't seen, so much as heard. Let's imagine you're on a mountain hike as elk bugle in the background until a vehicle passes by. It turns out, noise pollution does more than ruin an escape to the Great Outdoors. Research suggests if it goes unchecked, it puts wildlife at risk. Rachel Buxton is a conservation biologist who researched this with Colorado State University. Audio of elk bugling courtesy of Dr. Jacob Job, Sound and Light Ecology Team, Colorado State University.