Hughes, B. O., Dun, P. 1984. Production and behaviour of laying domestic fowls in outside pens. Applied Animal Ethology (Applied Animal Behaviour Science) 11, 201 (Abstract).

The birds outside produced on average as many eggs (337 in 560 days) as those inside (378), and of greater mean weight. ... Feather condition was better in birds in [outside] pens and their body weight was greater than that of controls in groups of four in battery cages. The main activities observed outside were grazing, ground pecking, ground scratching and dust-bathing.