On a cold April morning, I was suddenly woken up at 4 a.m. by the call of a koel sitting on the neem tree right outside my window. Koo-Ooo, Koo-Ooo. I resisted the urge to shake the branch and chase away the bird. At that moment, I had no inkling of the fascinating aspects of the koel’s various behaviors. The koel, or Eudynamys scolopaceous,is a member of the cuckoo order of birds (Cuculiformes). Male cuckoos are known for their distinctive calls and female cuckoos for laying their eggs in other birds’ nests. While other birds mate, build nests, lay eggs, incubate them and feed the chicks till they’re old enough, cuckoos don’t exhibit any parental behavior and instead trick other birds into taking care of their eggs. Although considered lazy and vain for abandoning its parental duties, we shall see that the cuckoo doesn’t have an easy life.
Female Asian Koel (Eudynamys scolopacea). (Image source: Doug Janson/WikimediaCommons, CC BY-SA 3.0)
Over a hundred species of birds lay their eggs in some other birds’ nests. Such birds are called ‘brood parasites’, and the birds that are thus parasitized are referred to as the ‘hosts’. This kind of outsourcing of parental duties has its advantages – cuckoos can lay more eggs in a season since they don’t have to invest in rearing their young, and cuckoo chicks don’t have to compete with each other because they’re raised in a host’s nest. Pied Cuckoo, Large Hawk Cuckoo, Indian Cuckoo, and Asian koel (or koel) are the predominant brood parasitic birds distributed across India. In this article, when I use the word ‘cuckoo’, it is a placeholder for any of the brood parasitic songbirds, though in most places, I use the specific example of koels to emphasize my point.
The cuckoo has captured the popular imagination for centuries and several cultures worldwide have portrayed the characteristic calls and behaviors of the cuckoos in stories and songs and myths. In many languages the bird’s name sounds like its call, for instance, it’s called coucou in French and kuckuck in German. The cuckoo’s arrival announces the arrival of spring, and in India, the arrival of cuckoos is also associated with the joy of blooming of mango trees. My grandfather, who is 89 years old and has lived in nine cities over 40 years of service in the Indian Postal Service, tells me that his most notable impression of the cuckoo is that, come spring, it sits on a mango tree and sings in the ‘most beautiful voice among birds’.
When I spoke about my interest in cuckoos and koels to my uncle, who is a scholar of ancient Indian texts, he told me about the 4th-century playwright and poet Kalidasa. In Kalidasa’s renowned play, Shakuntala, the amnesiac king, Dushyanta, who has forgotten his tryst with Shakuntala, refuses to accept her unborn child, suggesting that she is trying to pass off another man’s seed as his own. Dushyanta says-
“The female’s untaught cunning may be seen
In beasts, far more in women selfish-wise;
The cuckoo’s eggs are left to hatch and rear
By foster-parents, and away she flies”.
Cuckoos are migratory birds – the males arrive first, establish their territories and start singing to attract females. It is only the males that sing the tune that is so familiar to everyone. Once the females have mated, the hard part of the breeding season begins for them – sneaking their eggs into host birds’ nests. It is commonly said that cuckoos lay their eggs in the nests of crows. While it is true that the house crow (Corvus splendens) is the primary host of the Asian koel, other species of cuckoos in India and around the world target birds that are quite different from themselves – the incidental similarity of the adult koels or their chicks to crows appears not a necessary condition for successful parasitization. Arne Moksnes, a professor at the Norwegian University of Science and Technology, and his colleagues studied the interactions between Asian koel and its host species on the campus of Jahangirnagar University in Bangladesh. They found that the rates of parasitization were 11% for crows and 31% for the common myna.
B.S. Lamba, of the Zoological Survey of India, studied crows’ nest-building habits and parental behavior over four years in the 1950s. He found that for 14 weeks in the summer, male and female crows form close bonds and build a nest together. In the first week, the pair assiduously construct a nest with dry sticks and twigs and line it with grass, horsehair, feathers, and the like. Once the nest is ready, the female lays 3-6 eggs, one on each consecutive day. After putting in all this effort, imagine that an intruder flies in lays her own egg within a few seconds, and flies away, tricking the crows into bringing up a foreign chick while their own starve to death. Many would find such trickery ‘lazy’ on the cuckoo’s part, however, the cuckoo does a lot of grueling reconnaissance before it can complete its mission, and it does not always succeed.
The cuckoo is more often heard than seen and with good reason! When I asked an old schoolmate if she had ever seen a cuckoo, she said, “No, I’ve never seen one, but I’ve heard its song several times”. The female cuckoo strategically perches behind dense foliage to closely surveil potential host nests in her vicinity. She has to pick the nest very carefully.
The koel must carefully select her intended host nest. For each bird species, the eggs need to be incubated for a particular number of days before they are ready to hatch. Crow eggs hatch after 16-20 days of incubation, compared to koel eggs which hatch after only 13-17 days. Douglas Dewar, a British colonial officer at the turn of the 20thcentury, studied the parasitic habits of koels in Lahore. He reported that koel eggs always hatched before the crow chicks because the koel times her egg-laying perfectly – not before the crow has started laying, lest her egg gets rejected, and not too long after the crow has laid its eggs so that the koel chick doesn’t get outcompeted by crow chicks.
While other birds generally take about 30 minutes to lay an egg, the cuckoo can do it in seconds. How does she manage this? In his book, Cuckoo: Cheating by Nature (2015), Nicholas Davies, a professor of behavioral ecology at Cambridge University, U.K. describes this unusual egg-laying mechanism. While the female cuckoo is picking out the nest, she sits still and lets the egg descend the oviduct. She can hold it there and has immense control over the timing of the final release of the egg. She then waits for an opportune moment when the host from a suitable nest is away and quickly swoops in to deposit her egg and flies away, all within seconds! Sometimes, even if the host nest is occupied, she braves their attacks while laying her egg, risking significant injury or even death.
On an evolutionary timescale, one of the problems the cuckoos have had to overcome is host defense in the form of egg discrimination. The host birds are not passive to the cuckoo’s intrusion– if they detect a foreign egg in their nest, they instantly eject it. If they can’t distinguish the egg but know that their nest has been tampered with, they abandon it and build a new nest elsewhere. In response to such defenses, the cuckoos have evolved egg mimicry – the cuckoo eggs closely resemble that of the host species, down to the background color, the color, and distribution of their spots. Moksnes and his group found that, despite the koel’s efforts, the proportion of parasitized nests that produced at least one koel fledgling was 25% for crows, 33% for common myna, and 46% for long-tailed shrikes.
Finally, if the koel’s forgery goes unnoticed, the crows accept the koel egg and wind up becoming its foster parents. Now, the koel chick’s struggle begins. The koel egg hatches 3-4 days before the crow chicks hatch, taking advantage of being the lone mouth, and continuously begs for food. It soon gains weight and grows rapidly in the first few days before the new crow hatchlings begin to compete.
Asian Koel being fed by a Black-collared Starling. (Image source: Yifei He/WikimediaCommons, CC BY 4.0)
Dewar showed that unlike chicks of other cuckoo species which push the host eggs and chicks out of the nest even while the foster parents watch, the koel chick tolerates the crow chicks. When the foster parents arrive with a beak full of food, they are confronted by a number of gaping mouths as the nestlings raise their necks to beg for food. The koel chick, usually the largest, competes successfully for food by begging incessantly. When the weakest chicks don’t get enough food, they starve and die and are thrown out of the nest by their own parents. Lamba found that if a koel chick is present in the nest, two out of five crow chicks will die of starvation.
Davies also describes other strategies that cuckoo chicks use. In some species of cuckoos, the chick rolls the host eggs out of the nest and even evicts the host chicks. In the case of Horsfield’s hawk-cuckoo, the chick has yellow patches under its wings which is the same shade as its open gape. When the chick is quite hungry, it spreads its wings and calls loudly, which seems like three chicks are begging for food. Since the cuckoo chicks call loudly for food, they attract predators in many instances. So, the parasite chicks also exhibit some defensive behavior to stave off threats – they erect their head feathers, open their orange gape and suddenly snap it close, and they also release their foul-smelling brown liquid feces, if touched.
Once the chick is fledged and capable of finding its own food, the juvenile cuckoo leaves the host nest, only to return next summer as an adult to parasitize another host nest and never build its own. Many people only know of the cuckoo’s melodious voice and its habit of laying eggs in another’s nest. This incomplete picture of the cuckoo’s life often creates a misconception in people’s minds that it leads a carefree, lazy life, singing its days away. But in fact, the cuckoo leads a tough life – from the time it’s born, it has to compete for food in the nest, beg incessantly to be fed enough food, and ward off possible predators. Once it’s an adult, it spends its days surveilling potential host nests and risks its life to lay eggs. Life is hard for the cuckoo too!
Acknowledgements
This article is one of the essay assignments I have completed as part of my online internship under the mentorship of Prof. Raghavendra Gadagkar, Centre for Ecological Sciences, Indian Institute of Science, Bangalore. I spoke to several family members, neighbors, and friends to get an idea of how the cuckoo is popularly perceived. I’m grateful to them for their patience and indulgence.
Author:
Vasudha Kulkarni is an undergrad majoring in biology at the Indian Institute of Science Education and Research, Pune. She is broadly interested in animal behaviour, ecology, and evolution, intending to explore their intersection with conservation, climate change, and urbanisation. She’s an avid reader and besotted with written words, be it in books, articles, or letters. She is stepping into science communication and looks forward to writing more about her readings for a broader audience. Follow her on Twitter.
Editor:
Sumbul Jawed Khan is a Ph. D. in Biological Sciences and Bioengineering from the Indian Institute of Technology Kanpur, where she studied the role of microenvironment in cancer progression and tumor formation. During her post-doctoral research at the University of Illinois at Urbana-Champaign, she investigated the gene regulatory networks that are important for tissue regeneration after damage or wounding. She is committed to science outreach and communication and believes it is essential to inspire young people to apply scientific methods to tackle the challenges faced by humanity. As an editor, her aim is to simplify, translate, and excite people about current advances in science.
Illustrator:
Atharva Deshpande is a 4th-year student at IISER Mohali pursuing a Biology major and minor in Science Education who eventually wants to become a full-time science illustrator. He believes blending science, art, and storytelling makes for an interesting recipe. You can follow him on Instagram and Twitter or connect with him on LinkedIn.
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