From what I understand, cats adapt rather well to chickens, whereas not all dogs do. I think a chicken is such a large bird that a cat treats it with respect (especially after a peck on the nose) whereas they'd be happy to chase a sparrow.
If you hatched chicks, you'd have to keep them away from the cats until they were a bit more grown, though.
See the Omlet and Practical Poultry forums for much discussion on chickens v pets.