マダガスカル島における鳥類の群集構造と適応放散

抄録

This paper reviews studies on the community structure and adaptive radiation of Madagascar birds. Fission from Gondwana and formation of the Mozambique Channel before the evolutionary expansion of birds have caused a paucity of species number, a high level endemism and ecological release in Madagascar birds. Most forest bird species behave as mixed-species flocks. The guild structure of the community of Madagascar birds shows a unique configuration, with high proportions of 1) forest living species, 2) foliage gleaning species and frugivorous species, and 3) ground foraging species. Adaptive radiation is remarkable in the Couinae and Vangidae. In Couinae there are no large variations in morphology, and sympatric species have segregated micro-habitats. There are great variations in body size, bill shape and size, and foraging ecology (i. e. foraging location and technique) among the Vangidae. Species with similar bill morphology do not belong to the same foraging guild, with one exception. Members of the Vangidae forage primarily on boughs and trunks, filling the niche of woodpeckers. In the non-breeding season, the degree of aggregation varies from solitary pairs to large flocks, while territorial spacing out prevails in all Vangidae species in the breeding season. All of them are socially monogamous. Helping behaviour has been found in two species, Leptopterus chabert and Schetba rufa. Narrow ranges of variations in diet and habitat selection may have caused a lower level of variation in the mating system.