Breeding season of the Endangered White (Umbrella) Cockatoo, and possible competition for nest holes with Blyth’s (Papuan) Hornbill in North Maluku, Indonesia

Abstract

The White Cockatoo Cacatua alba is endemic to the North Molucca islands and is considered Endangered mostly due to unsustainable levels of trapping for the pet trade. Little is known about its breeding biology in the wild, except that it nests in tall trees during the early part of the year. We made brief observations of two active nests of White Cockatoos on Halmahera and another on Ternate in February and March 2014, and estimate the egg laying dates of two of these nests as mid-October and mid-November. Combined with other data, the breeding season appears to extend from October to May or June. All three nests were visited by Blyth’s Hornbills Rhyticeros plicatus, a species which occurs throughout North Maluku, as well as New Guinea. One nest was subsequently abandoned. In September and November 2014, we observed two active nest cavities of hornbills, one of which was inspected by a cockatoo, and the other, approached closely by cockatoos. Both hornbill nests were reported to have been used previously by White Cockatoos, suggesting that the two species may either share or compete for the same nest cavities. Sharing of cavities may be facilitated by partly non-overlapping breeding seasons, as Blyth’s Hornbill reportedly lays eggs from August to October in the region. However, as the nest cycle of both species is c.4 months, it is possible that early nesting pairs of one species may attempt to usurp nest cavities occupied by the other species. The potential for nest competition may be exacerbated on small islands where deforestation has reduced the number of nest cavities available for hole-nesting species.