http://www.eurekalert.org/pub_releases/2007-10/lsu-lps101507.php
Public release date: 15-Oct-2007
LSU professor studies army-ant-following birds
Certain tropical birds entirely dependent on ant swarms to flush out
prey
BATON ROUGE – In the jungles of Central and South America, a group of
birds has evolved a unique way of finding food – by following hordes of
army ants and letting them do all the work.
Robb Brumfield, assistant curator of genetic resources at the LSU
Museum of Natural Science and assistant professor of biological
sciences, first witnessed this peculiarity in 1989 when he accompanied
then-LSU graduate student Ken Rosenberg to Peru as an assistant.
“Rosenberg’s project investigated dead-leaf-foraging, which is a
specialized way that some tropical bird species have devised to find
food. These species find their insect prey by probing dead, curled
leaves suspended in vine tangles,” Brumfield said. But as he walked
endless jungle trails each day in search of these dead-leafing birds,
he became captivated by another novel approach some applied to hunting
for food: army-ant following.
With this type of specialization, flocks of birds track army-ant swarms
through the forest. “When millions of these army ants are on the move,
they consume every insect, spider and lizard they come across,” said
Brumfield. “Naturally, any animal that hears them coming – and they’re
very, very loud – runs the other way. The army-ant-following birds have
learned to take advantage of the swarm by perching above it and preying
on insects and other small animals trying to escape. It’s reminiscent
of the mockingbird that follows me when I’m mowing the grass, picking
off the insects that had been hiding there.”
Now, nearly 20 years after that first trip to Peru, Brumfield has again
teamed up with Rosenberg, who is now at Cornell University’s Laboratory
of Ornithology, along with Jose Tello of the American Museum of Natural
History and three other LSU researchers – Matt Carling, Zac Cheviron
and Nanette Crochet – to study the evolution of army-ant following.
“Over the last 50 years there has been some outstanding work on the
ecology and behavior of army-ant-following birds, but the details of
how the specialization evolved had not yet been examined,” Brumfield
said.
The team published their findings in this month’s issue of “Molecular
Phylogenetics and Evolution.”
“Using a hypothesis of the evolutionary relationships among antbird
species that we reconstructed from DNA gene sequences, what we found is
that army-ant following has been around a long time, possibly as long
as six million years, and that its evolution followed a logical
progression from least specialized to most specialized,” said Brumfield.
There are three main categories of specialization found in
army-ant-following birds. The first, called occasional army-ant
followers, are the most casual of the three, utilizing the insects to
round up food but only as the swarm passes through their territory.
Regular army-ant followers, the next level up in specialization, will
follow the army ants outside of the flock’s territory but are not
completely dependent on the ants to provide food. These birds regularly
hunt for themselves. The final, and perhaps most interesting, category
is that of the professional army-ant followers. These birds are
completely reliant on the army ants for food, presenting a problem
almost as unique as the situation itself.
“These birds depend almost solely on one species of army ant, called
Eciton burchellii,” said Brumfield. “This makes the professional
army-ant followers sensitive to many of the very real threats to this
ecosystem, like deforestation, global warming and other similar issues.
If anything affects the ant population, it could be devastating for
these birds. But what is perhaps most surprising is that, despite the
bird’s dependence on one primary ant species, the specialization has
persisted for millions of years.”
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