Internal security problems from the 1960s up until 1998 prevented any fieldwork in Cambodia. Since then, the situation has improved greatly and the Royal Government of Cambodia, in collaboration with international conservation NGOs, has been conducting general biological surveys across the country. Survey reports were used to investigate current occurrence of hornbills. Historically, three hornbill species — Great Hornbill Buceros bicornis, Wreathed Hornbill Aceros undulatus and Oriental Pied Hornbill Anthracoceros albirostris — were known from Cambodia. Recent surveys show that populations of Great and Wreathed Hornbills have declined significantly since the 1960s, while Oriental Pied is still common. A fourth hornbill species, Brown Hornbill Anorrhinus tickelli, was reported in 1998 in Kirirom National Park spanning the border of Koh Kong and Kompong Speu provinces in south-west Cambodia. Conservation priorities and priorities for future surveys are being developed.

We surveyed birds in two remnant patches of montane evergreen forest landscapes differing in intensity of habitat fragmentation, land use patterns and development. Present landscape configurations in Mae Tuen and Om Koi show that both became heavily fragmented (Table 1, see also Figure 1) between 1954 and 1996. The low abundance at Om Koi of large frugivores, such as Brown Hornbills Ptilolaemus tickelli and Great Hornbills Buceros bicornis, and their lack at Mae Tuen, are probably effects of prolonged fragmentation.

We examined the influence of forest fragmentation and resource availability on the abundance and distribution of Sumba Hornbill Aceros everetti, a large, canopy-dwelling bird endemic to Sumba Island, Indonesia. Hornbill numbers were estimated monthly from August 1998 to September 1999. Estimates were made in three large (≥1,000 ha) and three small (<1,000 ha) forest fragments, using a standard line transect method. Phenological patterns of canopy trees were assessed in 10 × 50 m plots. Our data indicated that forest patch size may be a better predictor of Sumba Hornbill abundance and distribution than overall resource availability. Hornbills occurred at higher densities in large forests (6/km2) than small forests (2.4/km2). Small forests produced more fruit/ha per month but lacked a number of important hornbill food species. Monthly fruit availability in large and small forest fragments had no significant effect on fluctuations in hornbill density. However, hornbill densities were significantly higher in forests with high densities of strangling figs, after controlling for patch size, and in larger forests hornbill densities correlated with the abundance of ripe figs. We hypothesize that small patches still have conservation value if they are within hornbill ranging distance, and speculate that Sumba's forests are in a dynamic phase before the full impact of fragmentation has been expressed.

Nest-site selection by the sympatric Great Hornbill Buceros bicornis, Wreathed Hornbill Aceros undulatus and Oriental Pied Hornbill Anthracoceros albirostris was investigated in a lowland tropical forest in Arunachal Pradesh, north-east India during 1997–2000. Information on two nests of Rufous-necked Hornbill Aceros nipalensis in higher-elevation forests is also presented. All species nested in live trees of three tree genera, 83% (n = 36) in Tetrameles nudiflora, an emergent deciduous softwood, relatively common in lowland foothill forests. No difference was recorded in nest-tree species or nesting habitats of sympatric hornbills, but there were a few differences in structural characteristics of nest-trees. Cavity size was the main variable separating the three species. Great Hornbills used larger cavities while Oriental Pied Hornbills used smaller cavities closer to riverine areas. Nesting was attempted at 64% of known sites and successful fledging of chicks was 80% overall (n = 72 nests, pooled over 4 years). Nest-trees in disturbed habitats near human habitation were used but were often abandoned or unsuccessful and 50% of all nest-trees were inactive by the end of the study. Potential large nest-trees had a density of 5.9/ha, that of the two most used species was 1.3/ha, and minimum nest densities of all three species was about 1 pair/km2. Interference competition for nest-sites was not observed, despite similarity in nest-tree characteristics, low nest density and high loss of nest-trees. Nest-site availability may naturally limit hornbill populations in the area, and additional loss of nesting habitat to human activities may exacerbate limited availability of breeding sites.

This study examines the diets of four hornbill species (Bushy-crested Hornbill Anorrhinus galeritus, Wreathed Hornbill Aceros undulatus, Rhinoceros Hornbill Buceros rhinoceros and Helmeted Hornbill Buceros vigil) common within our 9 km2 study area in the Bukit Barisan Selatan National Park, Sumatra, Indonesia. Line transects and opportunistic sampling were used over one year to collect feeding data, including the tree species and strata in which birds fed, diet items, fruit characteristics and tree crop size. Hornbills fed on 64 species. Figs, non-fig fruits and animals comprised 23.4% (n = 15 species) 51.6% (n = 33 species) and 25% (n = 16 species) of the diet, respectively. Although there was overlap among the diets of the four species, only B. rhinoceros and B. vigil had a statistically significant overlap, primarily due to high fig consumption by both species. B. vigil fed almost exclusively on figs (98.6% of the diet) and a small proportion of animals (1.4%) while 23.1% of the B. rhinoceros diet comprised non-fig fruits and animals (23.1%), with 76.9% figs. A. galeritus and A. undulatus had distinct diets with drupaceous, oily fruits comprising 66.7% and 64.4% of the diets, respectively. We found no significant relationship between the numbers of hornbills visiting fruiting trees and the characteristics of the fruit (weight, length and width). However, maximum crop sizes of diet species significantly influenced the number of feeding hornbills. Hornbill species also differed in the strata in which they fed. A. galeritus and B. rhinoceros were seen in the middle of the canopy 56% and 50.8% of the time, respectively while A. undulatus and B. vigil were observed more frequently in the upper canopy (50% and 74.3% of the time, respectively). The lower part of the canopy was used infrequently by all species. This study suggests that the four hornbill species in our study partition food resources by food type and/or feeding location.

This paper summarizes current knowledge and outlines future work on the breeding biology of Southern Ground Hornbill Bucorvus leadbeateri in Zimbabwe. All available records since 1900 were analysed, including casual reports by members of BirdLife Zimbabwe and published records. Estimates were made for the start and end of the breeding season, group sizes, clutch size and productivity levels, together with an assessment of preferred habitats and nest-tree species. There is a need for intensive fieldwork to determine aspects of breeding biology such as incubation and nestling periods. Particularly important for sound management and conservation strategies is relative breeding success in different land-tenure systems. The author has started work in a communal area 40 km south of Bulawayo city; land-use systems such as new resettlement areas, commercial farms and protected areas remain to be studied.

Food habits of Malabar Pied Hornbill Anthracoceros coronatus were studied from December 2000 to December 2001, in the Athikadavu valley, Western Ghats, India. A total of 147 individuals belonging to 18 fleshy-fruited tree species were monitored fortnightly. Thirteen fruit species, including five figs and eight non-figs, were recorded in the birds' diet. The overall number of tree species in fruit and fruiting individuals increased with the onset of summer, the Malabar Pied Hornbill's breeding season. The peak in fruiting is attributed to the peak in fruiting by figs. Figs formed the top three preferred food species throughout the year. During the non-breeding period (May to February), 60% of the diet was figs. During the peak breeding period (March and April), two nests were monitored for 150 hours. Ninety-eight per cent of food deliveries to nest inmates were fruits belonging to six species. Most fruits delivered at the nests constituted figs (75.6%). In addition, figs sustained hornbills during the lean season and should be considered “keystone species” in the riverine forest ecosystem. Two non-fig species are also important. Habitat features and local threats at Athikadavu valley were assessed. The distribution and conservation status of Malabar Pied Hornbill in the Western Ghats was reviewed. Conservation of hornbill habitats, particularly the lowland riparian vegetation, is imperative.

Asian hornbills are primarily frugivorous. We studied the characteristics of fruits consumed by four sympatric hornbill species in Thailand: Great Hornbill (Buceros bicornis), Wreathed Hornbill (Aceros undulatus), Austin's Brown Hornbill (Anorrhinus austeni) and Oriental Pied Hornbill (Anthracoceros albirostris). We compared the frequency of distribution of 11 variables for all fruit species collected in the study area (n = 259) and fruit species consumed by hornbills (n = 73). Our analysis revealed that fruits consumed by hornbills are: (1) large, (2) easily accessible within the canopy, (3) red, purple or black and (4) dehiscent or indehiscent with a thin husk. The range of fruit sizes eaten by hornbills in our study is comparable to that reported from other sites in Southeast Asia and Africa. The large gape width of hornbills enables them to consume large fruits that small frugivores would find difficult to consume.