If you believe honesty is the best policy, you would have a hard time
convincing the forked-tailed drongo. This tricky African bird is the
pathological liar of the animal kingdom.
Scientists described on Thursday how this medium-sized bird brazenly
deceives other animals by mimicking alarm calls made by numerous bird
species - and even meerkats - to warn of an approaching predator in a
ruse to frighten them off and steal food they leave behind.
The researchers tracked 64 forked-tailed drongos over a span of nearly
850 hours in the Kalahari Desert in South Africa close to the Botswana
border to unravel this unique behavior.
"They're rather demonic little black birds with red eyes, a hooked
beak and a forked tail," said evolutionary biologist Tom Flower of the
University of Cape Town in South Africa.
"They're also highly aggressive and are renowned for attacking eagles
and hawks, for which they apparently have no fear," added Flower, whose
study appears in the journal Science.
These birds, common in southern Africa, usually get meals the honest
way, such as capturing insects in mid-air using their superb aerial
skills.
But at other times, like on cold mornings when few insects are flitting around, the drongos turn to a life of crime.
FALSE ALARM
The drongos are able to mimic the sounds made by many different
species that inhabit its desert environment, including birds such as
pied babblers, glossy starlings, sociable weavers and pale chanting
goshawks as well as mammals like meerkats.
The drongos carry out an elaborate con. They give their own genuine
alarm call when they spot a predator approaching - essentially behaving
as sentries - and other animals come to trust that this call signals
real danger.
But they sometimes give this alarm call when no danger exists to fool other animals into fleeing and abandoning their food.
Then the drongos swoop down for a free lunch.
"All the animals in the Kalahari eavesdrop on each other's alarm
calls, which provide invaluable information about potential predators.
It's a bit of an information superhighway where all the animals speak
each other's language," Flower said.
"Because drongos give reliable predator information some of the time,
it maintains host responsiveness (of other animals) since they can
never know if the drongo is lying or telling the truth," added Amanda
Ridley, an evolutionary biologist at the University of Western
Australia, another of the researchers.
The scientists noticed that sometimes the other animals "get wise" to
the con and ignore repeated false alarm calls. But then the wily
drongos simply grab another tool from their toolbox of trickery - they
mimic the alarm calls made by other animals, once again conning them
into fleeing and leaving their chow behind.
Flower observed drongos mimicking more than 50 calls.
When stealing food from other animals, drongos are able to eat larger
prey than they normally would be able to capture on their own like
scorpions, beetle larvae and even geckos.
"Crime pays," Flower said, noting that the stolen stuff accounted for about a quarter of the food eaten by the drongos.
"One could argue that the strategy of the drongo to steal food from
others seems very dishonorable in human standards. But, yes, if it has
found such a crafty way to catch food, which is usually much larger than
the food items it catches itself, then we cannot help but admire this
clever little bird's adaptiveness," Ridley added.
The researchers classify the drongo as "a kleptoparasite."
There are many examples of mimicry and deception in the animal
kingdom. About 20 percent of song birds mimic the calls of other birds,
Flower noted.
"However, drongos are the only
ones to flexibly produce the specific signals that best deceive their
different hosts and to maintain their deception racket by changing
signal when the previous signal failed," Flower added.
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