By Will Dunham,
May 1, 2014
(Reuters) - 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.
No comments:
Post a Comment