Lone Rook

I live next to a small plantation and for about 3 years I’ve been feeding a very small group of rooks, they actually nested in a tall tree beside my house ( 3 nests) so it has been fab watching them nest and rear their young. Apart from this group there is a rook that comes down to feed but he is always alone. He is very scruffy and has a bad leg (it faces the wrong way around). He lets me get much closer than the other rooks so I’ve become rather fond of him or her! My question is why is he always alone? Is it because of his leg? He is definitely a rook and not a crow! 

Any thoughts?