Under cover of darkness, beavers are swimming through tranquil pools in the San Pedro River. They're gnawing on tree trunks. They're building dams.
We know this because of the work of volunteers who have recently walked miles along the river searching for signs of beavers.
Next to the piled branches of one beaver dam, a volunteer strapped a wildlife camera to a tree several months ago. And in the middle of the night, two beavers repeatedly turned up in the infrared images, their eyes glowing in the darkness.