Very early one morning in the Andamans, we were woken up by the persistent yowling of two tomcats fighting. Bleary-eyed, I walked out onto the balcony and looked down the forested slope. A few moments later, to my amazement, I realised that it was a greater racket-tailed drongo mimicking both sides of the catty argument. Shaking my head in disbelief, I listened to the bird's full repertoire which then moved on to the piercing call of a white-bellied sea eagle before going on to the sweet chirps of a tailor bird interspersed with a discordant truck horn! What was the point of this extraordinary mimicry?
Greater racket-tailed drongos hunt in feeding parties made of several species of birds. Sri Lankan ornithologists theorised that drongos may mimic different species to invite them to form such a group. But we don't know for sure if this is coincidence or deliberate use of mimicry.
While other birds are engrossed in foraging, drongos may act as sentinels, watching for predators. Should one sneak in, they sometimes mimic the alarm calls of various birds presumably to incite a mob attack. But they appear to mix up alarm and non-alarm calls.
A while ago, we witnessed a black drongo making loud shikra calls even as the predatory bird was within earshot feeding on a golden oriole chick. The neat trick certainly didn't drive the shikra away. It's not clear if drongos intentionally try to incite a mob attack. It is also possible that birds learn to repeat the sound when they are in a similar frame of mind (especially when they are stressed) as when they first learnt it.
Famously, some species such as parrots and hill mynas have learnt to talk. This aptitude may be reinforced as their human trainers reward them when they say the right thing. But parrots can imitate a vacuum cleaner, a ringing telephone, and even a barking dog without the benefit of such treats. Einstein, a famous African grey parrot at the Knoxville zoo, imitates wolves, chimpanzees, roosters, tigers, and a range of other animal neighbours. Of what use could such remarkable mimicry be in the forest where the parrots live?
Laura Kelley at Deakin University in Australia says parrots in the wild live in flocks and mimic each other to strengthen their social bonding. In captivity, they imitate the next best thing to a flock, their human companions.
The most spectacular bird mimic, the lyrebird, is a hit on YouTube. It can imitate a car reversing, camera shutter, chain saw, the sound of falling trees, rifle shots, musical instruments, fire alarms, crying babies, trains, humans, just about anything it hears. Since male birds go to great lengths mimicking human sounds during the breeding season, it has been suggested that females may be selecting males with the most diverse range of calls. But European biologists found no evidence that male songbirds with better imitating skills have their way with the ladies. Another, somewhat nihilistic theory suggests that mimicry may just be a learning error which serves no ultimate purpose.
Earlier this month, scientists reported that the drongos of the Kalahari make fake alarm calls to steal someone else's lunch! When the birds noticed a meerkat or babbler with a tidbit of food, they cried wolf. When the scared animal or bird high-tailed it to cover, dropping the prey in its haste, the drongos were quick to take advantage. So far this deception is the only proven function for vocal mimicry.
Could the miaowing racket-tailed drongo in the Andamans have been trying to wrest a tidbit? Only time and lots of observation will tell. Kelley cautions that the art of mimicry is widespread around the world and there may be no single explanation.
In the meantime, I marvel at the birds' ability to include dishwashers and ambulances into their repertoire, to use the environment as a living, vibrant musical alphabet. John Cage would have approved!
(The author can be reached at janaki@gmail.com)
