On the homeward leg of my round-the-US trip, I stopped at Prairie Homestead State Park, near Badlands National Park in South Dakota. Several Prairie Dogs were frolicking in the field, or - like this one - standing watch at the entrance to their home, warning others of the strange two-legged creatures in their midst.
(May 21, 2011. Nikon D5000, 1/500s @ f/8, 230mm, ISO 200.)