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Reproductive behaviour of the Eared Grebe, Podiceps caspicus nigricollis McAllister, Nancy Mahoney

Abstract

The present study describes and analyses the elements involved in the reproductive behaviour of the Eared Grebe and the relationships between these elements. Two summers of observation and comparison with the published work on the Great Crested Grebe give some insight into these elements, their evolution, and their stimuli. Threat and escape behaviour have been seen in the courtship of many birds, and the threat-escape theory of courtship in general has been derived from these cases. In the two grebes described threat plays a much less important role than the theory prescribes, and may not even be important at all. In the two patterns where the evolutionary relationships are clear, the elements are those of comfort preening. In the three patterns in which there is still some doubt, all the elements can be related to general non-reproductive behaviour or to nesting patterns. When courtship tapers off, nesting behaviour takes its place. The timing of this change and of the nesting behaviour patterns is caused by a general climatic stimulus followed by a more particular behavioural one. Nest-building and egg-laying are the results of the gradual building up of the sexual condition during courtship. Egg laying, however, takes place only in warm, dry weather. If the weather changes for the worse during laying, the birds stop and wait. The effect of this double stimulus is to put the birds on the borderline between determinate and indeterminate layers.

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