characteristic casques that distinguish them from other avian taxa. Hornbill casques contain foamy air-filled cavities surrounded by multiple layers of keratin tiles that act as an external shell. The extra weight of the casque is supported by the fusion of the first two vertebrae. The bill has distinctive serrated casques near the base of the upper mandible, which are particularly unique because of its ridges. As the birds mature, forward growth causes the foremost ridge to break off. It is hypothesized that specialized casque characteristics evolved due to multiple selection pressures, including its use for vocalization enhancement, physical pounding, mating displays, and as visual cues for age and social status. Distribution and habitat The wreathed hornbill inhabits tropical evergreen forests in the region from southern Bhutan, Northeast India, Bangladesh and through mainland Southeast Asia to Indonesia, where it is restricted to Sumatra, Java, Borneo and a few smaller islands. It has been recorded up to an elevation of . In Bhutan, two individuals were sighted in Sarpang district in spring 1986. In Northeast India, it inhabits unlogged primary forests and selectively logged forests in the foothills of the Eastern Himalayas from Nameri National Park in Assam to Namdapha National Park in Arunachal Pradesh. During the breeding season, it lives in lowland areas, but migrates to higher elevations in the non-breeding season. In Myanmar, 62 wreathed hornbills were sighted in the Mali River valley at elevations of in winter 1999. A flock of about 50 individuals was sighted in Hponkanrazi Wildlife Sanctuary in September 2004. Behaviour and ecology The wreathed hornbill is a social bird and most active in the early mornings when foraging for fruits; 21 individuals studied in Pakke Tiger Reserve during the non-breeding season rested at midday and resumed activity in the early afternoons. It lives in larger flocks than other hornbill species and remains in groups during both breeding and non-breeding seasons. Flock size observed in Namdapha National Park ranged from a mean of 4.7 to 6.6 individuals with a density of in March and April to in December. In Arunachal Pradesh, the wreathed hornbill density is much lower in habitats where local people hunt, ranging from . It travels long distances to forage for fruit, sometimes flying between islands, but it does not migrate. A male wreathed hornbill was fitted with a GPS tracking unit in Pakke Tiger Reserve during the breeding season; it moved a