Stormscape Warder  

Actually, their knees are NOT backwards... most animals including birds have the same leg / foot bone structure, primates (including humans) are the odd ones because we don't walk on just our toes. if you look closely, birds (including these Aviak models) have a hip joint then below that a knee joint that bends backwards then below that an ankle joint that bends forwards. They have a long bone below that that conects to their foot and toe structure which is what they actually contact the ground with.

Another thing to note is that birds have almost the same arm / hand structure as humans, just adapted into wings. Their "fingers" are their wingbones. =)