Nesting cycle and nest tree characteristics of the Helmeted Hornbill <em>Rhinoplax vigil</em>, compared to the Wreathed Hornbill <em>Rhyticeros undulatus</em>, in Sumatran lowland rainforest

Abstract

Hornbills provide a seed dispersal service for rainforest trees, but the persistence of hornbill populations depends on the availability of old trees that provide cavities for their nests. The Helmeted Hornbill Rhinoplax vigil is Critically Endangered, due to both forest destruction and an inhumane illegal trade in their bill casques, yet little is known about its nests and breeding biology. Here we describe the nest tree and external nest characteristics of a pair of Helmeted Hornbills in Bukit Barisan Selatan National Park, Lampung, Sumatra, and compare them with observations of two nests of the Wreathed Hornbill Rhyticeros undulatus less than 1 km away. As in a previous study, the Helmeted Hornbill (HH) nest was in a large dipterocarp, and possessed a stump next to the entrance that the male used as a perch when feeding the female or chick. The nest entrance dimensions and bole diameter of the nest tree were much larger than those of the two Wreathed Hornbill (W1 and W2) nests. Egg laying in HH took place in February, while in W1 and W2, eggs were laid much later, between late May and July. The maximum nesting cycle of the Helmeted Hornbill was an astonishing 137 days (4.5 months), close to the minimum period (range, 138-151) for a nest of the species in Peninsular Malaysia. This may be longer than the nesting cycle of the Wreathed Hornbill, but additional data are needed.