While elk hunting in Colorado over the last 2 weeks I came across some bolder fields and an animal call I had heard on the internet but never live.  This was from a tiny mammal that I have been trying to photograph in Yellowstone for a number of years but they had just alluded me.  With a 65# backpack on, with about 4 miles down and 2 miles to go, I heard the call.  It kind of sounds like a dog's squeaky toy.  With the priority in the trip being archery elk hunting, and my backpack already pretty heavy, I did not take a big lens with me.  Later in the week, I got go back to this boulder field with my 50mm lens to take some shots.  These are extremely cropped down.

Pika are considered an indicator species for global warming as they cannot tolerate hot temperatures.  With warming trends, their habitat continues to decline.  Pikas can die in 6 hrs if exposed to temps above 78 degrees.  

http://en.wikipedia.org/wiki/American_pika - Additional info on the Pika.

Uncropped photo to show what I was working with.