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Pika (Ochotona princeps) are a type of lagomorph that like to live in rock piles in the mountains. They are very vocal, making a high pitch squeek as an alarm call. Apparently they also sing during breeding season and the fall.
It is possible (just barely) to see a pika in the blog-sized version of this picture. I recommend clicking on the image to enlarge it for a more reasonable challenge though. I think the uncropped version might make a fun jigsaw puzzle.