Observations on the breeding biology of the Writhed-billed Hornbill (Aceros waldeni) in the Philippines

Summary We report on some aspects of the breeding biology of the critically endangered Writhed-billed Hornbill (Aceros waldeni) on the island of Panay, Philippines. Observations were made at three nests during 1995–1997. Walling-in of the females commenced in the first week of March. One female remained incarcerated for 77 days, two of three broods completed fledging around May 20 (1995, 1997). Details on fledging of the female and her brood and postfledging care by both parents are reported.The food of the males at two nests was ca. 98% fruits and 2% invertebrates. The plants exploited comprised at least 14 species. Over a third of the fruits delivered were figs of a small number of species.Two males had average feeding rates of 0.56 and 0.88 times per hour respectively, and fed 1 to 66 (median 8) items per feeding visit at the nest. The hourly feeding rate increased after hatching, but the composition of the diet did not change noticeably. As a rule, food items were delivered singly and, during one visit, in runs of one, or rarely up to 3, species.In the three weeks following vacation of the nest, the male appeared to be the sole food provider while the female stayed continually with the 3 young (as sentinel?) in the vicinity of the nest.The nest environs were defended by the male against Tarictic Hornbills (Penelopides panini panini). Six vocalisations of the parents are mentioned. One was used in territorial skirmishes with Tarictic Hornbills.With perhaps less than 30 pairs of the Writhed-bill surviving, the future for the species looks bleak. Only drastic conservation measures can prevent the species' demise. Some have been started by the PESCP.This paper is publication No. 11 of the Philippine Endemic Species Conservation Project (PESCP) of the Frankfurt Zoological Society.