Fascinating life of the Indian grey hornbill
Baljit Singh

A female poised to enter a natural cavity to begin nesting.
A female poised to enter a natural cavity to begin nesting. ó Photo by writer

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. This is one of the most fascinating marvels of evolution, which provides the Indian Grey hornbill a fair chance both against predation and for successful annual procreation of its species. The architecture of its bill is another amazing attribute of the evolutionary processes; the three-inch long crescent-shaped beak, with a protuberance on top resembling a horn, imparts to the bird on overall formidable look. In fact, it is hollow and spongy from inside, is compressed flat on the outer sides and more importantly, can securely hold four to seven ficcus berries at any one time without so much as a single dent on them.

The nesting and house-keeping ways of hornbills are a unique features of their lives. They always nest in a natural cavity, mostly on tree trunks. The cavity is eight to 13 inches deep and about eight inches wide with an opening, the like of a front-door entry or at times closer to the roof level like a sky-light entry. 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 masonís 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. Evolution at its best yet again.

The female is now completely a prisoner and is solely dependent on the male for her daily intake of food. The male rises to the occasion with uncommon devotion as he 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 in each sally is at times as much as 18 berries from a ficcus tree. The total period of this activity may scale up to 75 days. Without a break, or else the female and or the chicks will surely perish. Through this entire period, the male enters into a mute phase, lest he may give away the location of the nest to predators. Once your ears have been attuned to the shrill hornbill calls, the months of April or May appear strange and eerie.

The slit opening, besides keeping predators away, has two other vital functions. As is evident, it allows space for the female to open her beak to receive the food from her partner. The male comes and clings to the tree trunk just below the slit with his claws and regurgitating the berries, he drops them one at a time into the open beak of the female. The other most vital function is to keep the cavity clean of all excreta. Through a genetic impulse, the female aligns her vent opposite the slit and ejects her excreta down to the ground. The chicks too are born with this instinct.

As the chicks grow and the space in the cavity gets over-crowded, the female begins to enlarge the slit from top and bottom till it resembles the hour-glass. 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.

There are two nest-cavities in Chandigarh, both on Silver-oak trees about 1 km apart, which I have watched every February to June, from 2002 to 2004. If you want to see for yourself, use powerful binoculars and a tele-zoom lens on your camera. Comply with the code of keeping away from the nesting birds and their nestlings.