View with a difference

Hope you aren't getting too fed up of my Bald Eagle shots, LOL! The close photos are always taken at the Zoo (probably a good thing that I don't get THAT close to one in the wild, anyway : )). The angles, colours (especially of the background) always seem to come out differently - which leads to the temptation to upload, LOL. This particular bird was all fluffed up and seemed to be shivering. I've seen this happen before on another occasion. I wonder if this is "normal" behaviour and, if so, what is the reason?