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Comportement et structure sociale chez le manchot empereur

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Title: Comportement et structure sociale chez le manchot empereur
Author: Jouventin, Pierre
Abstract: A study of the ecology, behavioural repertoire and social struc ture of the Emperor Penguin (Aptenodytes forste ri) was under taken during the 1969 breeding cycle at Pointe Geologie, Adélie Land (Artarctica). During the study period, the sea ice was unusually solid and durable : this influenced both the chronology of the breeding cycle and chick mortality. Some 440 ringed birds were observed, almost daily. There was a majority of female birds possibly due to greater predation on males. The « fidelity rate » (duration of pair bonding) between mates from one year to the next was low, though some 3- and 4- year pair bondings have been observed. Of the 216 breeding birds observed in 1967 and 1969, only 2 % were not present in 1968. Thus the Emperor Penguin appears to breed annually, in contrast to the King Penguin, Aptenodytes patagonica. It is thought that males become sexually mature at about 6 years, females slightly earlier (one female ringed as a chick bred in its fourth year). During the study, 54 pairs were ringed and separated ; 92.60 % of these pairs were subsequently reformed. A group of breeding penguins, which lost its way to the colony and did not break up until the chicks were hatched, was used as a natural experiment for elucidation of problems of « homing » and direction finding, and for evaluation of minimum colony size in the species. A study was made of the origin and significance of the species’ behaviour patterns, some of which were so ill-defined that they appeared to be displacement activities. The frequency of occur rence of these activities, especially away from the colony, was studied by presenting groups of penguins with quasi-natural problems. The ontogenesis of behaviour was studied and acoustic signals of the species recorded and analysed. Differences in « song » between the sexes was noted, and a brief study of the circadian rhythm was made. Examination was made of specific releasers in the species, which appears to have practically no mechanisms for sexual iso lation. One releaser of sexual behaviour appeared to be the posi tioning of the body in a copulatory pose. The egg has a more complex function ; it both removes the inhibition of « singing » between paired birds during the preposital period and prevents feet movement of adults during the egg stage. The function of different signals was studied throughout the breeding cycle. Acoustic signals proved to be the most significant. The « mating song » has at least two functions : identification of sex and identification of the individual. A preposital silence of 1 i months possibly precludes any confusion between these two functions. There nevertheless appears to be critical aspects in the social system of the species. The presence of « trios », birds « keeping company » and un-mated individuals apparently result from ambiguities in the principal acoustic signal, from the excess of females and, most importantly, from the absence of territorial barriers. The behavioural repertoire of this highly gregarious species presents certain contradictory aspects. Though there is no nesting site to defend, there still remains a form of territorial behaviour. Chicks are fed individually, though elements of communal feeding behaviour can be recognized. The hypotheses of Stonehouse on the species’ colonisation of the Antarctic are discussed, supported and developed, from an ethological viewpoint. A general interpretation of the social structure of the species is presented ; this tries to give meaning to seemingly enigmatic behaviour patterns and social pheno mena. It is argued that reproduction at low temperatures has led to a series of behavioural characteristics not dissimilar to those observed in A. patagonica. It is suggested that these adap tations comprise : — loss of behaviour patterns that no longer have any func tion (sexual isolation mechanisms during courtship, « swinging walk » to attract the female to the territory) ; — suppression of potentially detrimental attitudes (« territo rial » defense, individual distance) ; — development of such adaptive behaviour patterns as social thermoregulation and preposital silence ; — persistence of patterns with little apparent significance (« sideways head sweeping ») ; — persistence of patterns that are necessary for successful breeding (mutual display bowing, mating song, trumpeting, flipper clapping). The social system of the Emperor Penguin, which apparently includes no real territory or hierarchy, seems to be closely adapted to the needs for social thermo-regulation. The absence of rigid structures may explain the sexual promiscuity that can be obser ved, particularly at the end of the breeding season.
Publisher: Société nationale de protection de la nature et d'acclimatation de France, Paris (FRA)
Date: 1971

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