i. To playback of calls of one of their chicks and calls of a foreign chick, parent Laughing Gulls responded by orientation towards the sound, approach, and calling in reply. They showed no discrimination between calls of their own chick and calls of the foreign chick. Response to the playback waned during testing when all the parent's chicks were absent, but not when one was present. 2. When gulls were tested by having one of their own chicks and a foreign chick placed in covered boxes near the nest, they responded more to their own chick than to the foreigner. This appeared to be because their own chick called more than did the foreigner. The results were consistent with the possibility that individual recognition of the parent's voice by a chick causes the chick to behave in ways that tell the parent whether the chick belongs to it or not. 3. The parents' behaviour in response to chick calls in these two sets of tests differed between families of different ages in ways that exemplified the natural progression in patterns of parent-chick interactions, and suggested some speculation about the course of social development in this species.