Some behavior patterns of 4 closely related grebes podiceps nigricollis podiceps gallardoi podiceps occipitalis and podiceps taczanowskii with reflections on phylogeny and adaptive aspects of the evolution of displays

Fjeldsa, J.

Dansk Ornitologisk Forenings Tidsskrift 76(1-2): 37-68

1982


Accession: 006439893

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Abstract
Antagonistic and courtship displays on 4 closely related species, the blacknecked grebe and the south american hooded, silver and Taczanowski's grebes are described. The species are gregarious and colonial. This may be associated with the feeding habits and with selection of rather open lake and marsh habitats, where dense clumping on the most protective places may give the best protection of the eggs. The species are opportunistic breeders, and synchronized egg-laying, possibly needed as a protective device, may require that the courtship involves infective group-displays. In connection with the development of social breeding, stationary threat typical of territorial relatives is suppressed. Aggression consists mainly in unritualized, mobile attack-escape sequences. Aggression leads to displays also used in courtship. The pair formation rituals are described in detail, their contexts demonstrated statistically and their significnce and possible evolution discussed. Courtship involves a variety of highly stereotyped and conspicuous displays. The complex discovery ceremony probably plays a central initiating role in the pair formation. Both this and some other rituals appear to have evolved from attack and fight behavior, and curiously the development of colony-breeding has not caused a reduction of aggressive elements in the courtship. Individual recognition and testing of other birds' ability to perform well may, as a supplement to the water-courtship rituals, be tested by infective platform-courtship and promiscuous mating. In silver and Taczanowski's grebes, aggression towards males advertising for a partner do not usually lead to open hostility. Instead males make parallel barge-dive dislays apparently competing in a ritualized way for the attention of females. Silver grebes were studied both with the closely allied Taczanowski's and hooded grebe. The comparisons give no direct evidence that courtship rituals evolve by selection against hybridization in zones of sympatry. Ethological differences between the silver Grebe races raise needs for future studies in possible contact zones to establish whether they are in fact different species. The ethology data substantiate that the 4 species form a monophyletic branch of Podiceps, with horned, red-necked and great crested grebes forming the sister group. The nearest outgroup may be the western grebe, while the great grebe should be omitted from Podiceps.