Ardea
Official journal of the Netherlands Ornithologists' Union

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Burger A.E. (1979) Breeding biology, moult and survival of Lesser Sheathbills Chionis minor at Marion Island. ARDEA 67 (1-2): 1-14
Lesser Sheathbills Chionis minor were studied at Marion Island in the sub-Antarctic. All breeding adults held territories in penguin colonies; virtually all food eaten by these adults and their chicks was obtained from penguins, mostly by kleptoparasitisme; and, the sheathbills bred when food from penguins was most freely available. The minimum age of first breeding was three years and there was a surplus of potential breeding adults. Clutches were one (3%), two (47%), three (47%) or four eggs (3%) and the average laying interval between successive eggs was four days. Eggs within a clutch were similar in size and in hatching success. Growth and survival of chicks, however, differed within broods (first-hatched chicks fared better) and this was related to hatching asynchrony. The adaptive significance of brood reduction is discussed. The mean reproductive output was 1.07 fledglings per pair per year. The advantages of nidicolous chicks and cavity nests are discussed in relation to the sheathbills' close association with penguins, the inclement weather and the presence of predators. Breeding adults moulted immediately after the breeding season and other, non-breeding birds moulted earlier. Breeding adults had a mean annual survival of 88%; non-breeding adults and subadults (combined) 49% and juveniles 37%. Apparent causes of mortality were starvation, inclement weather and predation by Sub-Antarctic Skuas Catharacta antarctica and feral cats Felis catus. The population on the island appears to be close to its carrying capacity and limited by the number of territories which can be established in penguin colonies.


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