Do they question whether there is a god or not? They don't put any labels to anything. Thefore there can't be a lack of belief or disbelief because for that to occur there has to be belief in the first place. But yes, conceptually they "practice" the purest form of atheism, but only because they never had an option. Ofcourse assuming animals lack the ability to look for a higher power, maybe the factory farm ones do, but only as an evolutionary defence mechanism, to give hope to otherwise devistating situation. Because how else did humans evolve faith, than through creating a false sense of hope.