Scramble competition in newborn domestic rabbits for an unusually restricted milk supply

Rabbit pups, Oryctolagus cuniculus, are nursed only for about 3 min once every 24 h, and we have previously reported indirect evidence of strong competition among littermates for the mother's milk. In the present study, we examined the nature of this competition more closely. In experiment 1, we investigated the temporal pattern of milk intake during nursing and found that pups obtain almost all milk available to them each day during the second minute of a 3-min nursing event. In experiment 2, we investigated the availability of milk across the eight nipples and found a tendency for more milk to be available from the two middle pairs. In experiment 3, we observed the behaviour of pups beneath the mother during nursing and found no evidence of a fixed 'teat order,' of overt aggression, or of pups displacing one another from nipples. However, the results confirmed previous findings of a positive correlation between milk intake and pups' birth weight. In experiment 4, the attempt to increase competition among pups by covering half of the mother's nipples did not lead to the expression of overtly aggressive behaviour or to recognizable displacements from nipples. We conclude that in the rabbit, littermates compete for milk by scramble rather than by contest competition, in which the heaviest pups have a clear advantage. It is a strategy presumably well suited to a situation in which milk is effectively available only for 1 min every 24 h, leaving little time for aggressive tussles.