The ontogeny of the pecking response of laughing gull chicks

Hailman reported that wild-reared laughing gull, Larus atricilla, chicks peck preferentially at models of laughing gulls over models of herring gulls, L. argentatus, but newly hatched chicks have no species preference, and respond equally well to an isolated red bill. The experiments reported here confirm these observations. They also suggest that the pecking of newly hatched chicks is guided by heterogeneous summation. A new working definition of heterogeneous summation is presented. Furthermore, the results suggest that species preference does not develop spontaneously with maturation or on the basis of imprinting, but rather from reinforcement and conditioned inhibition or habituation. It appears that learning can take place only to a model with high releasing value for pecking, and that the crooning call of adult laughing gulls has no major effect on pecking in newly hatched chicks.