Sunday, April 7, 2013


Hornbills are a group of birds whose bill is shaped like a cow's horn, but without a twist, sometimes with a casque on the upper mandible. Frequently, the bill is brightly coloured.

There are 57 species worldwide and 1 species which occurs in Pakistan is Indian Gray Hornbill (Ocyceros birostris) Hornsbill belongs to family Bucerotidae and Order is Coraciiformes.

Indian Grey Hornbill has grey feathers all over the body with a light grey or dull white belly. The flight feathers of the wing are dark brown and whitish tipped.

The horn is black or dark grey with a casque extending up to the point of curvature in the horn.  The upperparts are greyish brown and there is a slight trace of a pale supercilium.

The ear coverts are darker.  The tail has a white tip and a dark sub terminal band. They have a red iris and the eyelids have eyelashes. The casque is short and pointed.

It is a medium-sized hornbill, measuring around 61 cm (24 in) in length.  The male has a larger casque on a dark bill while the culmen and lower mandible are yellowish.

The bare skin around the eye is dark in the male while it is sometimes pale reddish in females. The female has a more yellowish bill with black on the basal half and on the casque. The juveniles lack the casque and the bare skin around the eye is dull orange.

They are found in pairs or small groups.

They are almost completely arboreal and very rarely descend to the ground where they may pick up fallen fruits or dust bathe.

They descend to the ground also to pick up mud pellets for sealing the nest cavity during the nesting period. They indulge in various social activities which include bill-grappling and aerial jousting.

The flight is heavy and involves flapping interspersed with glides. The call is a squealing call.  

The nesting season is April to June and the clutch varies from one to five very symmetrical white eggs.  Males display by fluffing up their feathers and spiral in the air appearing like a green, black, yellow and white ball.

When it is time to lay the first egg, the female hornbill enters the chosen nest-cavity and does not step out into daylight again, for as much as 75 days later. The male carries food to the nest at an average once every hour from dawn to dusk When chicks arrive, the frequency of visits doubles and the volume of food.

Indian Grey Hornbills usually nest in tree hollows on tall trees. The  nest is hollow and spongy from inside and  compressed flat on the outer sides. The female enters the nest hollow and seals the nest hole and leaves only a small vertical slit that the male uses to feed her. 

The cavity is eight to 13 inches deep and about eight inches wide with an opening. The nest entrance is sealed by the female using its excreta and mud-pellets supplied by the male. While inside the nest, the female moults her flight feathers and incubates the eggs. The re-growth of the feathers in the female coincides with the maturity of the chicks at which point the nest is broken open.

Having entered, the female lays a clutch of three to five eggs over the next five to seven days. She uses this pre-incubation period to also wall up the entrance to the nest cavity. The materials she uses for the wall are her own ordure (excreta), mud supplied in small lumps by the male from the outside and chips of wood picked out by the female from the inside of the cavity. The chemistry of the ordure is such that when mixed with the other two ingredients, the paste adheres rapidly like a mass of baked clay. Picking the mixture bit by bit she piles it painstakingly and using the flat sides of her bill as a mason’s trowel, she smoothens the surface and perseveres till the opening is sealed, leaving just one vertical, narrow slit of some two cms width and five cm height. The presence of wood chips in the plaster lends the finished wall the same texture and colour as the bark of the host tree trunk.

As the chicks grow and the space in the cavity gets over-crowded, the female begins to enlarge the slit from top and bottom . The day it is ripe for her to exit, the middle portion is demolished at one go and at long last she emerges in the open, free once again. Now at this stage, the genetic instinct for survival takes over the chicks who with combined efforts, wall up the opening all over again..


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