Background Seven out of ten hornbill species in the Philippines are threatened with extinction. Among these is the endangered Visayan Hornbill (Penelopides panini), found on the islands of Panay and Negros. Threatened by habitat loss and hunting, its population size is thought to have declined from 1800 individuals 20 years ago to less than 1000. However, a recent study on Negros estimated 3564 individuals across three core forest blocks. This study aims to quantify the Visayan Hornbill population size in and around the Northwest Panay Peninsula Natural Park (NWPPNP) on Panay, the largest contiguous low-elevation forest landscape remaining across its range, and its broad habitat associations across a gradient of environmental degradation. Methods Hornbills were surveyed using 10-min distance sampling point counts (n = 367) along transects (average length 1.1 km). Environmental variables were recorded along transects, while habitat was classified into primary forest, secondary forest, plantation, or open habitat. Distance software was used to estimate population densities stratified by habitat, with the overall population estimate taken as a mean of habitat density estimates weighted by habitat area. Using generalized linear mixed models, hornbill occurrence was modelled using combinations of nine environmental variables as main and two-way fixed effects. Results Surveys covered 204.4 km2 of the 374.8 km2 Northwest Panay Peninsula. Hornbills were not recorded in plantations or open habitats. Hornbill density was significantly higher in primary forest (17.8 individuals/km2 ± 26.9% CV) than in secondary forest (3.7 individuals/km2 ± 33.2% CV; z = 15.212, P < 0.001). The overall population estimate for the NWPPNP and environs is 2109 individuals, and 2673 individuals for the entire Northwest Panay Peninsula. Hornbill presence was best explained by a model including distance from the Park boundary alongside five interaction effects and transect as a random effect. Distance, and the interaction between distance and medium-sized trees were significant predictors of hornbill presence. Conclusions Our study evidences the habitat preference of the Visayan Hornbill, highlights the importance of the NWPPNP for the species’ conservation, and provides strong evidence for re-assessing the global population size.

Summary The Philippines is a global biodiversity hotspot, with a large number of threatened bird species, one of which is the ‘Critically Endangered’ Negros Bleeding-heart Gallicolumba keayi. The aim of this study was to investigate the habitat preference of the Negros Bleeding-heart and undertake species distribution modelling to locate areas of conservation importance based on identified suitable habitat. A survey of 94 point-counts was undertaken and eight camera traps were deployed from May to August 2018 in the Northwest Panay Peninsula Natural Park, Panay, Philippines. Habitat variables (canopy cover, understorey cover, ground cover, elevation, presence of rattan Calamus or Daemonorops spp. and pandan Pandanus sp., tree diameter at breast height, and branching architecture were measured in 5 m-radius quadrats. To identify areas of potentially suitable habitat for the Negros Bleeding-heart, species distribution was modelled in MaxEnt using tree cover and elevation data on Panay and Negros. Using a Generalised Linear Model, Negros Bleeding-heart presence was found to be significantly positively associated with dense understorey cover and dense canopy cover. Species distribution modelling showed that the Northwest Panay Peninsula Natural Park is currently the most suitably located protected area for Negros Bleeding-heart conservation, while protected areas in Negros require further law enforcement. It is imperative that protection is continued in the Northwest Panay Peninsula Natural Park, and more survey effort is needed to identify other critical Negros Bleeding-heart populations, around which deforestation and hunting ban enforcement is strongly recommended.

1The Philippines is a global biodiversity hotspot, with a large number of Threatened bird species, 2 one of which is the Critically Endangered Negros Bleeding-heart Gallicolumba keayi. The aim of this 3 study was to investigate the habitat preference of the Negros Bleeding-heart and undertake 4 species distribution modelling to locate areas of conservation importance based on identified 5 suitable habitat. A survey of 94 point counts was undertaken and eight camera traps were 6 deployed from May to August 2018 in the Northwest Panay Peninsula Natural Park, Panay, 7Philippines. Habitat variables (canopy cover, understorey cover, ground cover, altitude, presence of 8 rattan and pandan, tree diameter at breast height and branching architecture) were measured in 9 93 5 m-radius quadrats. To identify areas of potentially suitable habitat for the Negros Bleeding-10 heart, species distribution modelling was undertaken in MaxEnt using tree cover and altitude data 11 on Panay and Negros. Using a Generalised Linear Model, Negros Bleeding-heart presence was 12 found to be significantly positively associated with high understorey cover and dense canopy cover. 13Species distribution modelling showed that the Northwest Panay Peninsula Natural Park is 14 currently the most effectively located protected area for Negros Bleeding-heart conservation, while 15 protected areas in Negros require further protection. It is imperative that protection is continued in 16 the Northwest Panay Peninsula Natural Park, and more survey effort is needed to identify other 17 critical Negros Bleeding-heart populations, around which deforestation and hunting ban 18 enforcement is strongly recommended. 19 20

Seven out of 10 hornbill species in the Philippines are threatened with extinction. Among these is the Endangered Visayan hornbill Penelopides panini, found on Panay and Negros islands. Threatened by habitat loss and hunting, its population size is thought to have declined from 1,800 individuals 20 years ago to less than 1,000. However, a recent study on Negros estimated 3,564 individuals across three core forest blocks. This study aims to quantify the Visayan hornbill population size in and around the Northwest Panay Peninsula Natural Park on Panay, the largest contiguous low-elevation forest landscape remaining across its range, and its broad habitat associations across a gradient of environmental degradation.