BARRO COLORADO ISLAND,
Panama—Here in the dour understory
of the Panamanian rain forest,
the best way to find the elusive
and evolutionarily revealing
spotted antbird is to stare at your
boots because sooner or later you
will finally step into a swarm of
army ants boiling out across the
forest floor.
At that point you should step
right back out of the swarm and
start looking for the characteristic
flitting and hopping of the thrushsize
antbird, listening for its vibrato
“peee-ti peee-it” call. Because
wherever there are army ants out
on a hunting raid, peckish antbirds
are almost sure to follow.
The birds are not foolish
enough to try to eat them: Army
ants are fiercely mandibled and
militantly cohesive. Instead, they
hope to skim off a percentage of
the ants’ labour, by snatching up
any grasshoppers, beetles, spiders
or small lizards that may jump to
the side in a frantic attempt to
elude the oncoming avalanche of
predatory ants.
It’s a gleeful reversal of the
conventional notion of parasites
as little, ticky things that plague
large, poorly dressed hosts. Here
the big vertebrates are the parasites,
freeloading off insects a
fraction of their size.
And the parasitic strategy is
so irresistible that according to
recent research in the journal
Ecology, the spotted antbirds on
Barro Colorado Island just may
be taking it professional. Janeene
M. Touchton a researcher
associated with the Smithsonian
Tropical Research Institute and
Princeton, and the principal author
of the report, is now trying
to identify the personality traits
that may facilitate a spotted
antbird’s leap from amateur to
polished parasite.
The antbird story also demonstrates
the vividly baklavaian nature
of parasitism in a tropical
rain forest. Researchers have
identified three species of butterfly
that specialise in following
antbirds. The butterflies feed on
bird droppings, and these butterflies
know where their suppliers
are likely to be found.
“I always end my talks by
showing a slide of this complex,
quadruple-tiered relationship,”
said Joseph Tobias of the University
of Oxford, who studies
antbird song and has worked
with Touchton. “You have the
ants themselves, followed by a
gaggle of antbirds, and behind
the antbirds are the butterflies,
and behind them are a couple of
bird watchers.”
Antbirds belong to an old and
almost purely tropical avian family
of some 200 species, only a
fraction of which have anything
to do with ants. The new research
looked at three swarmstalking
species that live in the
same region of Panama: the spotted
antbird, the slightly larger bicoloured
antbird and the even
larger ocellated antbird.
In the new work, the researchers
compared the standard
three-part scrimmaging of
antbirds seen on the Panamanian
mainland with the situation on
Barro Colorado Island, where the
ocellated antbird recently went
extinct. They expected that the
bicoloured antbirds on the island
would be the biggest beneficiaries
of the loss of competition.
Instead, it seems that the
spotted antbirds are the ones
making the most of the newly
opened niche. For one thing,
while the island’s population of
bicoloureds has stagnated, the
number of spotted antbirds is on
the rise. In tricky field experiments
just now under way,
Touchton is using checkered flags
to determine whether antbirds
that score low in neophobia—
fear of the new—are the ones
most likely to roam. As she explained,
if ants are always on the
move, their true moochers must
follow. Home, for them, must be
where the swarm is.
Panama—Here in the dour understory
of the Panamanian rain forest,
the best way to find the elusive
and evolutionarily revealing
spotted antbird is to stare at your
boots because sooner or later you
will finally step into a swarm of
army ants boiling out across the
forest floor.
At that point you should step
right back out of the swarm and
start looking for the characteristic
flitting and hopping of the thrushsize
antbird, listening for its vibrato
“peee-ti peee-it” call. Because
wherever there are army ants out
on a hunting raid, peckish antbirds
are almost sure to follow.
The birds are not foolish
enough to try to eat them: Army
ants are fiercely mandibled and
militantly cohesive. Instead, they
hope to skim off a percentage of
the ants’ labour, by snatching up
any grasshoppers, beetles, spiders
or small lizards that may jump to
the side in a frantic attempt to
elude the oncoming avalanche of
predatory ants.
It’s a gleeful reversal of the
conventional notion of parasites
as little, ticky things that plague
large, poorly dressed hosts. Here
the big vertebrates are the parasites,
freeloading off insects a
fraction of their size.
And the parasitic strategy is
so irresistible that according to
recent research in the journal
Ecology, the spotted antbirds on
Barro Colorado Island just may
be taking it professional. Janeene
M. Touchton a researcher
associated with the Smithsonian
Tropical Research Institute and
Princeton, and the principal author
of the report, is now trying
to identify the personality traits
that may facilitate a spotted
antbird’s leap from amateur to
polished parasite.
The antbird story also demonstrates
the vividly baklavaian nature
of parasitism in a tropical
rain forest. Researchers have
identified three species of butterfly
that specialise in following
antbirds. The butterflies feed on
bird droppings, and these butterflies
know where their suppliers
are likely to be found.
“I always end my talks by
showing a slide of this complex,
quadruple-tiered relationship,”
said Joseph Tobias of the University
of Oxford, who studies
antbird song and has worked
with Touchton. “You have the
ants themselves, followed by a
gaggle of antbirds, and behind
the antbirds are the butterflies,
and behind them are a couple of
bird watchers.”
Antbirds belong to an old and
almost purely tropical avian family
of some 200 species, only a
fraction of which have anything
to do with ants. The new research
looked at three swarmstalking
species that live in the
same region of Panama: the spotted
antbird, the slightly larger bicoloured
antbird and the even
larger ocellated antbird.
In the new work, the researchers
compared the standard
three-part scrimmaging of
antbirds seen on the Panamanian
mainland with the situation on
Barro Colorado Island, where the
ocellated antbird recently went
extinct. They expected that the
bicoloured antbirds on the island
would be the biggest beneficiaries
of the loss of competition.
Instead, it seems that the
spotted antbirds are the ones
making the most of the newly
opened niche. For one thing,
while the island’s population of
bicoloureds has stagnated, the
number of spotted antbirds is on
the rise. In tricky field experiments
just now under way,
Touchton is using checkered flags
to determine whether antbirds
that score low in neophobia—
fear of the new—are the ones
most likely to roam. As she explained,
if ants are always on the
move, their true moochers must
follow. Home, for them, must be
where the swarm is.
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