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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 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. 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. |
