About Ocyceros birostris (Scopoli, 1786)
Ocyceros birostris, commonly known as the Indian grey hornbill, is a medium-sized hornbill that reaches approximately 61 cm (24 in) in length. Its upperparts are greyish brown, with a faint pale supercilium, and darker ear coverts. Its wing flight feathers are dark brown with whitish tips. Its tail has a white tip and a dark subterminal band. Individuals have red irises, eyelashes on their eyelids, and a short, pointed casque on the bill. Males have a larger casque on a dark bill, with yellowish culmen and lower mandible, and dark bare skin around the eye. Females usually have pale reddish bare skin around the eye, and a more yellowish bill with black coloring on the basal half of the bill and the casque. Juveniles do not have a casque, and have dull orange bare skin around the eye. This species is mainly found on plains up to around 610 m (2,000 ft), ranging south from the Himalayan foothills, bounded to the west by the Indus system and to the east by the Ganges Delta. It may make local movements in the drier western region, and can even be found in cities with old avenue trees. It has been observed, usually in pairs, in Dharamsala town, Himachal Pradesh at approximately 1500 to 1600 meters above sea level during summer and the rainy season from May to September 2017. It does not overlap much in range with the Malabar grey hornbill of the Western Ghats. The Indian grey hornbill's call is a squeal similar to that of a black kite. Its flight is heavy, consisting of bouts of flapping interspersed with glides. It occurs in pairs or small groups. Its nesting season runs from April to June. Clutch size ranges from one to five very symmetrical white eggs. Indian grey hornbills typically nest in tree hollows in tall trees; they may further excavate an existing hollow to suit their needs. The female enters the nest hollow and seals the nest entrance, leaving only a small vertical slit that the male uses to feed her. The female seals the nest entrance using her own excreta and mud pellets supplied by the male. While inside the nest, the female moults her flight feathers and incubates the eggs. The male brings a steady supply of bark pieces to the nest to absorb waste and maintain the cavity's micro-climate. The regrowth of the female's flight feathers aligns with the maturity of the chicks, at which point the nest is opened. A study of a nest near Mumbai found that the key fruiting trees this hornbill feeds on are Streblus asper, Cansjera rheedii, Carissa carandas, Grewia tiliaefolia, Lannea coromandelica, Ficus spp., Sterculia urens and Securinega leucopyrus. Indian grey hornbills also eat molluscs, scorpions, insects, small birds (they have been recorded removing and possibly preying on rose-ringed parakeet chicks), and reptiles. They are known to feed on the fruits of Thevetia peruviana, which are toxic to many vertebrates. They are almost completely arboreal, only very rarely descending to the ground to pick up fallen fruits, take dust baths, or collect mud pellets for sealing the nest cavity during the nesting period. They engage in various social activities, including bill-grappling and aerial jousting.
