Monitoring of nests of the Visayan Tarictic Hornbill Penelopides panini panini on the Philippine island of Panay revealed thus far undescribed information on the breeding biology of this species. Females occupied nest holes in March–April, after which two or three eggs are laid. Although cooperative breeding is suspected for the genus, at two nests no helpers were recorded. Nest-concealment behaviour was observed in the adult male. After a nestling period of 55–58 days, the adult female and one juvenile left the nest simultaneously. Immature birds resemble their respective sex. Nest site characteristics of 24 nests of the Tarictic Hornbill and two of the Writhed-billed Hornbill Aceros waldeni, respectively, were recorded on Mt Balabag, Panay Mountain Range. Tarictic Hornbill nests were situated in living as well as dead trees, at an average height of 11 m. Cavity compass direction was uniformly distributed around the circle. Nests are aggregated within the habitat, with a mean nearest-neighbour distance of 190 m. Writhed-billed Hornbills may require larger trees for nesting than Tarictic Hornbills. Nest density was calculated to be around three Tarictic Hornbill nests and 0.2–0.3 Writhed-billed Hornbill nests per square kilometre. Given a total amount of suitable hornbill habitat on Panay of 225–450 km2, about 750–1,000 Tarictic Hornbill breeding pairs and 60-100 Writhed-billed Hornbill breeding pairs may remain on Panay.
Breeding biology, nest site characteristics and nest spacing of the Visayan Tarictic Hornbill Penelopides panini panini on Panay, Philippines
