The Response of Incubating Laughing Gulls (Larus Atricilla L.) To Calls of Hatching Chicks

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Abstract
Observations on Laughing Gulls suggest that calls emanating from pipping eggs are responsible for several behavioural changes typical for the transition from incubation to parental behaviour. In order to study the role of vocalisations unconfounded by tactile stimuli provided by pipping eggs, calls recorded from a hatching chick were played to incubating birds from underneath the nest-cup and their effects were observed. Incubating gulls responded to such calls by an increase in the frequency of the following behaviour patterns: looking down, rising-resettling, shifting the eggs, quivering while sitting and calling. Qualitatively new, parental behaviour patterns were not quantitatively recorded, but were seldom observed in response to the calls. In contrast to earlier experiments with tactile stimuli, nest-material manipulations and the proportion of incomplete settling movements were not significantly affected by these auditory stimuli. An inverse relationship was found between the strength of responsiveness to chick-calls and the number of nest-building movements performed during the experiment. Tests carried out at different stages of the incubation period revealed that the responsiveness to chick-vocalisations increases as a function of progressing incubation. A preliminary experiment was performed to test for the selectivity of the response. Incubating birds responded more strongly to the calls played to them at normal speed than at half the speed (which changes the calls' pitch, frequency modulation and temporal characteristics).

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