Really nice game, but as others already said, there should be some kind of indicator on each animal to tell how much space it needs. This was a lot of trial and error and eventully frustration. If you don't want to show the exact numbers, maybe just have some smiley faces next to each animal which would show how close you are for them to be happy. Eg.:
:-( you are more than 2 squares off
:-| you are 1-2 square off
:-) the size is right