Love the shot of the squirrel, but as mentioned the background is quite noisy. Do you set your ISO manually or allow the camera to do it? I'm not too familiar with the D5100, but it ISO 2500 meant to be usable?
Again, the shot is still great!
Jonathan
My eye isn't as tuned as most on this site, so I can only really comment on what I like - and I really like #3 - I think the interaction of nature and man-made objects is really interesting and grabs my attention.
Good job