When August comes, it is
time for the urban birdwatcher to regale himself with the drama of the
crow and the koel, and witness the humbling of the wily crow by a more
cunning adversary. In most areas that have tall eucalyptus or gulmohar
trees, it is an interesting sight to see a few pairs of common crows (Corvus
splendens) busily feeding raucous young ones of the koel (Eudynamys
scolopacea).
To the discerning eye,
the differences in the parents and the chicks are vividly marked as far
as their appearances and the sounds are concerned, but these do not seem
to matter at all for the crows. To their parenting instinct, it is
enough to know that the squawky little fledglings, consistently
clamouring for food, came out from their nests and hence are nothing but
their own brood. More often than not, such a brood may not contain even
a single crow chick because nature ensures that the larger size and
early hatching ability of the parasitic bird results in the host loosing
its own clutch, and raising only the young of the parasitic bird.
This then, is a classic
example of nest and brood parasitism exhibited in some birds. It is a
remarkable reproductive strategy in which one species - the brood
parasite – does not build its own nest, but chooses to lay its eggs in
the nest prepared by another species. It is this host species that
hatches the eggs and later raises the brood parasite's young to
adulthood.
The hosts of brood
parasites do exhibit some initial defense mechanisms against the
usurping of their nests. They may resort to either camouflage or
concealment of their nests, or else guarding them aggressively by
constantly chasing possible intruders from the vicinity of the nest. But
ironically, it is this aggressive behaviour of nesting crows that is
easily transformed into successful egg-laying by the koel. As the
irritated female crow dashes madly after the male koel that has been
ceaselessly needling her while she sits in her nest, the female koel
quickly slips into the vacated nest and lays her clutch. She may, if she
gets the time, push out some of the crow eggs, but her primary concern
is to lay her own before the female crow returns. This done, she quietly
flits away to leave the nest back in the possession of the rightful
owner, returning triumphantly from the chase.
It is obvious that the
female crow is not able to distinguish either the koel’s eggs from its
own, or notice the change in their numbers after the koel has added her
clutch to the nest. This shows that although the crow is universally
regarded as a cunning bird it certainly is naïve when it comes to
counting chicks before they are hatched. Taking all the eggs in the nest
as being their own, both parents continue to hatch them. Later, when the
chicks emerge, they too are not recognized as imposters but raised by
the crows as their own. Being early hatchers, the koel chicks usually
emerge before the crow chicks, and in the process negate any chance for
the crow eggs in the nest to hatch. Feeding these ravenous chicks is the
only duty that the crows can perform for the next few weeks. Even if a
crow chick does manage to hatch, it is usually bullied to starvation by
its larger foster sibling. That is the reason why one may not come
across a crow pair feeding a joint brood containing both crow and koel
chicks. It is probably when the young koels are grown and ready to fly
away to an absolutely different tune, that the stumped foster parents
realize the goof-up.
One may wonder
ceaselessly at the sequence of events that go into this unique natural
phenomenon But the cycle of life goes on happily for the crow and the
koel, with both species proving to be quite successful breeders, as is
evident by their healthy numbers in our midst.
Which is
unfortunately what we can’t say for too many species anymore....