Wildlife on higher ISO

I like going out to nature and I plan some destinations where to go to and take photo of wild animals. As I was not sure how the higher ISO values will affect picture quality in reality I took my APS-C camera, telephoto lens and went to the forest park to shoot. No one except deer were able to stand as models, generally it does not matter. Results are here. Not so bad for ISO 1600. If I buy better lens I can shoot in the near future in the same manner.