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A comparative study of some of the social communication patterns of cormorants and related birds in the Pelecaniformes. Van Tets, Gerard F.


A comparative study was made of the social communication patterns of Pelecanus erythrorhynchos, P.onocrotalus, P.crispus, P.occidentalis, Morus bassanus, Sula sula, Anhinga anhinga, Phalacrocorax carbo, Ph.auritus, Ph.olivaceust Ph.aristotelis, Ph.urile, Ph.pelagicus, Ph.penicillatus, and Fregata magnificens. It was found that the signal patterns are combinations of a limited number of discrete postures, movements, and sounds, and that they are mainly derivatives from four main sources, locomotion, fighting, nest-building, and begging. The take-off was found to consist of three phases, look, crouch, and leap. From the look and crouch phases the Suloidea have evolved their pre-take off displays, while from the recovery after landing they have evolved their post-landing displays. The pre-take off and post-landing displays are combined into a hop display in this super-family. The sky-pointing, a male-advertising display of Sula, is a derivative of the pre-take off display of Morus and is the origin of the wing-waving as a male-advertising display in Anhinga and Phalacrocorax. The throw-back which is the second part of the male-advertising display of Phalacrocorax arlstotelis is a derivative of the wing-waving display of the other cormorants. Threat displays have evolved into recognition displays in the bill-raising of the Pelecanidae, the head-throwing of Sula sula, the gaping of the Phalacrocoracidae, and into the first part of a male-advertising display, the darting, of Phalacrocorax aristotelis. Nest-indicating displays have evolved from the reaching for nest-material into the reach-bowing of Pelecanus erythrorhynchos, and from nest-worrying movements into the wave-bowing of P.erythrorhynchos, the wing-bowing of Moras, the front-bowing of Sula sula, the quiver-bowing of S.leucogaster and S.dactylatra, the snap-bowing of Anhinga anhinga, the front-bowing of Ph.aristotelis and the gape-bowing of Ph.melanoleucus. The food-begging displays of the chicks have evolved into the pre-landing displays of the Pelecaniformes which in some species also serve as recognition and male-advertising displays on the nest site and in the Sulidae, Anhingidae, Phalacrocoracidae, and Fregatidae accompany the transfer of nest-material between members of a pair at the nest site. The food-begging derived displays also include the aerial displays of Pelecanus erythrorhynchos, the head-wagging of the Sulidae, the kink-throating of the Anhingidae and Phalacrocoracidae, the rattling of the Fregatidae, and the aerial displays of the Phaethontidae. From a comparison of the taxonomic distribution of the form, function and derivation of the social communication patterns in the Pelecaniformes, it was concluded that they reflect the phylogenetic implications of the current systematic classifications of the order.

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