In 2008 and 2009 a total of 29 Crested Ibises
Nipponia nippon were introduced to Sado Island. In 2010, six pairs attempted to breed for the first time since their release and built eight nests in total. Five of six pairs laid eggs in six nests, although none of them resulted in successful hatching. We observed by telescope five nests attempted by four pairs between March and May in 2010, and recorded nest-building and attending behaviors to reveal sexual differences in parental roles. The ibises built open nests in trees. During the nest-building stage, males collected most of the nest materials (branches, twigs, and leaves), whereas females engaged principally in arranging the materials brought by males. After egg-laying, both males and females brought leaves to the nest for the inner lining. Males and females took turns incubating eggs, but the relative contribution of males varied among the pairs. Two of the four pairs stopped their breeding attempts by abandoning incubation, and one pair took the eggs out of their nest. The remaining pair abandoned their first clutch for an unknown reason, and their second clutch was preyed upon by a Large-billed Crow
Corvus macrorhynchos. In the two pairs that abandoned incubation, the males increased nest attendance as the females decreased incubation time, until they finally deserted the nests. Thus, the abandonment of incubation appeared to have been initiated by females, whereas males tended to stay longer at their nests to continue incubation. To ensure the successful reintroduction of the Crested Ibis, the causes of nesting failure need to be clarified.
View full abstract