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 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.
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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.
(Reporting by Will Dunham; editing by G. Crosse)
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