Breeding Biology of the Luzon Hornbill Penelopides manillae manillae (Aves: Bucerotidae) on Luzon Island, Philippines

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The Luzon Hornbill Penelopides manillae manillae, one of the smallest hornbills in the Philippines, is endemic to the lowland forests of Greater Luzon. Due to the intensifying threats of deforestation and wildlife poaching, this species has been uplisted to Vulnerable in the Philippine Red List. However, despite this concerning situation, ecological data on the species remains limited. In this paper, we present information on tree and cavity characteristics, nesting diet, some aspects of breeding biology, and the first description of the nesting behavior of the Luzon Hornbill. We examined seven nests in the Subic Watershed Forest Reserve by using single rope climbing techniques. One nest was monitored for 75 hours from March to June 2022 to acquire data on nesting diet and behavior. Luzon Hornbill nests in natural cavities in live, large-girthed trees particularly White Lauan Shorea contorta (Dipterocarpaceae). Cavity opening dimensions (W×L) ranged from 6.5–16 cm×8.5–34 cm with vertical depths (floor to ceiling) of 34–300 cm and a mean depth of 3.86±4.91 cm, suggesting a preference for shallow cavities with high ceilings and small entrances. The male hornbill delivered food (mainly the fruits of 32 species of plants) through the cavity slit 11–27 times a day. Investigation of the nests post-fledging revealed elytra of jewel beetles (Buprestidae) and intact shells of land snails. The female hornbill was estimated to have remained within the cavity for approximately 90 days. Cooperative breeding, as has previously been reported for the genus Penelopides, was not observed in this study. Our findings provide vital information that may guide the development of conservation tools and forest management policies that aim to increase foraging and nesting opportunities for breeding hornbills.