Mrs Hema Ramachandran, wife of Veteran General PK Ramachandran, posted this image on her Facebook of a Koel (Eudynamys Scolopaceus) who visits her garden. 

I was reminded of our grandfather who narrated to us young children as to how the Koel laid her eggs in a House Crow’s (Corvus Splendens) nest.  His narration was to teach us to be industrious as a crow and not be lazy and cunning as a Koel.

When we were in Grade 10 at Sainik School Amaravathi Nagar, Mr Paul Sathya Kumar (MPSK) taught us Biology.  He explained various tactics in the bird/ animal/ plant kingdom to prove the survival of the fittest theory, and one such case was that of a smart Koel who laid her eggs in a crow’s nest.

The Koel is known as a brood parasite – a species that imposes the cost of rearing its offspring onto another species – the host (House Crow) – by laying its eggs in the hosts’ nests.

Is Koel Lazy?  Is she more industrious than the crow?  Is she crafty and cunning?

In Sanskrit and Telugu language it is called as Kokila, Thamizh, Kannada, Malayalam –കുയിൽ, குயில்  (Kuyil), Hindi-कोयल  (Koel.)  Many good female singers are referred to as Koel or Kuyil.  Does the female Koel sing?  No! It is the mating call of the male bird to woo the female bird. 

For almost nine months of the year, the Koel is seldom seen because it neither sings nor calls except in the breeding season – April to July.  It is difficult to spot a Koel due to its shy nature and secretive behaviour.  They mostly remain hidden inside leafy foliage and go undetected, by and large.

In their breeding period, birds mate, lay eggs, rear their offspring and protect them. In India, birds usually breed in summer because their chicks will have enough food in the following monsoon.

Koel is a case of mimicry in the bird kingdom.  Its eggs resemble those of the crow in pattern and colour.  The ground colour of the crow eggs presents different shades of bluish green while that of the Koel is olive green. Eggs of both host and parasite have similar brown markings in the form of blotches, specks, and streaks, which are more densely distributed towards the broader end. Although eggs of Koel are smaller in size, they exhibit remarkable mimicry with crow eggs.

To ensure a higher chance of clutch formation (clutch is the number of eggs laid,) the Koel cleverly lays an egg in the crow’s nest when the mother/father crow is not around and then throws away one of the crow’s eggs.  

That means the crows can count and the mother crow is unaware of the replacement.

Another reason as to why the Koel leaves its egg in the crow’s nest is that the Koel is a vegetarian. Newborn chicks need a lot of protein to grow, and the crows will feed them non-veg protein.

This is a survival instinct and is basically inherent in the genes of organisms in nature.  It further proves Darwin’s theory of ‘Survival of the Fittest.‘

There are other examples of brood parasites in the bird kingdom. The egg of the common Hawk Cuckoo (Hierococcyx Varius) mimics that of its host species, the Jungle Babbler (Turdoides Striata) in size and colour. Such mimicry is thought to have evolved to prevent the host from rejecting any eggs.

Host birds respond to brood parasites using different defence strategies. They attack the parasite outright at times, and at others issue warning calls, hide the nest, look for and remove the parasite’s eggs and aggressively defend their territories.  I have often spotted female Koels being chased by crows even outside the nest when they spot each other.

A Koel is so crafty that to increase the chance of survival of its eggs, she lays her eggs in different nests.  Remember the adage – ‘Never put all your eggs in the same basket!‘  When the Koel visits a crow’s nest, it also punctures or breaks eggs irrespective of the species so that her offspring isn’t starved of food even during a shortage.  The Koel is too smart to ensure that the clutch size is optimum so that the crow can feed and take care of its chicks. 

If a host happens to see a parasite laying an egg in its nest or recognises an intruding egg, it will abandon the nest or reject the egg.

Incubation period of the Koel’s egg is about 12 to 13 days and the crow’s 16 to 17 days.  Thus, the Koel chicks emerge a few days before the first crow chick hatches.  The poor crow hatches the eggs, feeds the Koel chick, and brings it to adulthood to hear the bird coo differently.

The Koel chick keeps chirping continuously. So, the mother crow feeds it more thinking that the chick is still hungry and not yet fed enough.  The Koel chicks grow rapidly and become healthier than the crow chicks.  They develop feathers and wings earlier than crow chicks and fly out earlier.

Isn’t the Koel industrious, crafty and cunning than the crow??