Well here are the creatures hidden in the terrain pieces (clockwise from top left) :
1) a tiny frog right in the middle of the crater's puddle.
2) the second crater hides a rat sitting on the edge of the middle between the two puddles.
3) there's a green woodpecker on one of the wire posts.
4) The last crater has some blown up wire and on the largest post is an owl.
Well done to all who spotted them!