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THE EGG‐ROLLING OF BLACK‐HEADED GULLS LARUS RIDIBUNDUS

1962; Wiley; Volume: 104; Issue: 3 Linguagem: Inglês

10.1111/j.1474-919x.1962.tb08665.x

1474-919X

Colin Beer,

Animal Vocal Communication and Behavior

SUMMARY Model eggs were placed at the edges of the nests of gulls, and the number of models that were rolled into the nests within a certain time was recorded, for all stages of the reproductive period. The results indicate that the readiness to perform egg‐rolling increases steadily as the date of laying draws closer, remains maximally high during the laying and incubation periods, and declines steadily after hatching. This pattern is similar to the distribution found for other responses with an incubation function. A model egg was fixed at the edges of a number of nests of gulls in the incubation period. A gull could attempt to roll but the model would not move. Gulls with eggs in the nest and gulls with their eggs removed from the nest were tested in this way! The presence of the fixed model disrupted incubation behaviour to a certain extent, and the presence of the eggs resulted in the birds performing fewer rolling attempts, and a greater proportion of intention rolling movements, than when the nest was empty. Thus when the tendency to settle and sit and the tendency to roll an egg from outside the nest are both highly activated, they can interfere with each other. There was no evidence that nest‐building movements appear as displacement activities when the egg‐rolling action is prevented from being carried through to completion, or when the tendency to stay sitting in the nest and the tendency to rise and roll an egg are in balanced conflict.