Verheyden C, Jouventin P
Centre d'Etudes Biologiques de Chizé, Centre National de la Recherche Scientifique, F-79360, Beauvoir/Niort, France.
Oecologia. 1991 Mar;86(1):132-139. doi: 10.1007/BF00317400.
The Lesser Sheathbill Chionis minor is an opportunistic predator and scavenger that breeds on sub-Antarctic islands during the summer season, when many other seabirds are present, especially penguins on which it is kleptoparasitic. It is a poor flyer and over-winters on its breeding grounds, where it faces a diminished food supply and low temperatures. Its foraging behaviour was suspected to be plastic enough to respond to such a variable environment, and we show how this species enlarged its niche to survive in winter. Population movements, dietary changes and monthly weight gains were quantified during a 13-month period of observation. Mortality rates, calculated over a 19-year period of banding, appeared to be age dependent: they decrease, due to competition, from juveniles to subadults, adult non-breeders, and breeders. One of the survival strategies described here is, to our knowledge, unique among birds. After the Crested Penguin colonies have been deserted, some adult sheathbills (mainly females) remained territorial, extending their territory size and diet while their partners moved to previously undefended zones in King Penguin colonies (permanent and large in the Crozet archipelago), where they competed for a winter territory and subsequently associated with another mate. After this winter mating, mobile sheathbills returned the following summer to their breeding territory and previous mate.
南极小鸊鹈是一种机会主义的捕食者和食腐动物，夏季在亚南极岛屿繁殖，此时有许多其他海鸟，尤其是企鹅，它会对企鹅进行盗食寄生。它飞行能力较差，在繁殖地越冬，那里食物供应减少且气温较低。人们怀疑其觅食行为具有足够的可塑性以应对如此多变的环境，我们展示了该物种如何扩大其生态位以在冬季生存。在为期13个月的观察期内，对种群移动、饮食变化和每月体重增加情况进行了量化。在为期19年的环志期间计算出的死亡率似乎与年龄有关：由于竞争，从幼鸟到亚成鸟、成年非繁殖鸟和繁殖鸟，死亡率逐渐降低。据我们所知，这里描述的一种生存策略在鸟类中是独一无二的。凤头企鹅群落被遗弃后，一些成年鸊鹈（主要是雌性）仍占据领地，扩大其领地范围和饮食，而它们的配偶则转移到王企鹅群落（克罗泽群岛的永久性大群落）中以前未被占据的区域，在那里它们争夺冬季领地，随后与另一个配偶结成伴侣。经过这个冬季交配期后，活动的鸊鹈在次年夏天回到它们的繁殖领地和原来的配偶身边。
