I use kangaroo exclusively for the hawks/falcons/owls here at the Black Hills Raptor Center. Even the thinnest stuff is so tuff that the great horned owl doesn't chew thru them. Best of all it is the softest and most supple leather available. It wears very comfortably on their ankles.
Good thing the 'roo rawhide is so strong, otherwise you might feel "jumpy" when you shoot the bow.