Dawkins, M. 1977. Do hens suffer in battery cages? Environmental preferences and welfare. Animal Behaviour 25, 1034-1046.

The really rather surprising result of this experiment was the lack of demonstrated preference for either the [barren] pen or the [barren] battery cages. ... Once reason why a preference was not demonstrated may have been that the chickens did not regard the pen as sufficiently different from the battery cages to exhibit a preference between them (both pen and battery cage were inside, and the main differences were that the pen was larger and had the floor covered with wood shavings). ... These results show that battery-kept hens prefer an outside run to a battery cage, once initial unfamiliarity with the run has been overcome. ... Birds which have been living outside consistently prefer the run over the battery cage to a very marked extend.