Cockatoos using both eyes in turn

I’ve noticed that cockatoo ssp (Sulphur-crested, Galah and Gang-gang) all seem when they are perched and deciding whether to approach something or fly down to it, to examine the situation first with one eye, then with the other. I know they don’t have binocular vision, but in birds who do not are the two eyes different in some respects (light wave-length receptiveness)? are they getting different information from each eye, or are they just being ultra-cautious? — John Leonard Canberra