ORGANISATION, CONTROL AND DEVELOPMENT OF PARENTAL FEEDING IN OYSTERCATCHER (HAEMATOPUS OSTRALEGUS)

I. The transport and presentation of food to the young Oystercatcher is described. The parents will present food to the young either on their own initiative or in response to the approach of the young. 2. The auditory and tactile interactions between the hatching eggs and the incubating parents are described. As hatching proceeds both the parents and young become more responsive to each other, and both show marked selective responsiveness. These pre-hatch interactions lead to the transition from incubation behaviour to brooding behaviour and to the onset of parental feeding. It is suggested that the young may learn to respond to the call of the parent before hatching. 3. Both non-breeding and breeding birds show the same cyclical pattern of total feeding activities and it is suggested that self-feeding and parental feeding are part of the same motivational system. Once the food has been presented to the young, the subsequent behaviour of the parent is dependent upon the speed with which the young seizes and eats the food. If the young reacts within a certain time (the Waiting-Time Threshold) then the parent will present more food, and will continue to do so for as long as the young reacts within the threshold time. In this way feeding trains are initiated and maintained. The feeding train is broken off once the young fails to react within the threshold time. As the young grows older the parent plays an increasingly minor part in the initiation of feeding trains, the role of the young becoming more important. This leads to the eventual breakdown of parental feeding which is closely correlated in time with how long it takes the young to learn to feed itself. A model of the motivation and control of parental feeding is described. 4. It is suggested that parental feeding evolved in the Oystercatcher subsequent to the evolution of a specialised feeding behaviour which very small young were unable to