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Shortly before dawn I reach the river
that I must cross to enter my rain-forest study site in
Sulawesi’s Bogani Wartabone National Park. Foiled again! For
the gazillionth time, I spy my bamboo raft peacefully floating
off the opposite bank. It’s a lot less peaceful on my side as
I yank off my boots and leech-proof socks, roll up my
trousers, and start wading, muttering a curse on the brazen
borrower of my raft.
Once I’m in the forest, though, my soggy
spirits soar at the sight of an enormous fig tree towering 150
feet in the air and bearing thousands of ripe fruits. Hmmm, it
seems as if the park’s fruit-eaters have yet to discover this
valuable resource.
I start to walk on, but I catch a slight
movement out of the corner of my eye . . . then another . . .
and another . . . . Within seconds, the entire canopy comes
alive. In this one tree, there must be at least 200 fruit
pigeons of eight species—all at first hidden to me by their
excellent camouflage, but now frantically feeding on figs.
Their whirring wingbeats fill the air, and bungled and
rejected fruits rain on the ground. These fallen figs will
become a feast for yet more pigeons—elegant emerald doves and
handsome ground doves.
Then, as if someone flipped a switch, the
commotion ceases. Some of the pigeons leave the tree, but most
perch motionless, once more lost to sight. Their crops full,
they’ve settled down to digest their meals.
I record my data and resume my walk. For
the next two years, I will continue to examine the feeding
ecology and conservation of fruit pigeons and other
fruit-eating birds in Bogani Wartabone, one of the most
important protected areas in North Sulawesi.
But despite its protected status, park
land is still being cleared for agriculture and degraded by
gold mining, logging, and the harvesting of rattan. Hunting
for bushmeat poses a serious problem as well. My research is
part of WCS’s efforts to conserve Sulawesi’s rich biodiversity
through on-the-ground ecological research, training local
conservation professionals, and raising conservation awareness
through education. WCS has also spearheaded a collaborative
conservation management program, the Bogani Management
Council, and a Wildlife Crimes Unit to curb illegal bushmeat
hunting.
“Pigeon” and “conservation” are two words
that most people don’t expect to read in the same sentence. I
know this from the many bewildered faces and “Are you mad?”
looks I receive when I mention that I’ve studied pigeons for
so long. That’s because most people’s familiarity with the
pigeon family, Columbidae, comes through the rock dove,
Columba livia, which flourishes in cities. And there is little
love lost for this prolific “winged rat” whose droppings often
are considered both a nuisance and a health hazard.
Outside cities, however, there is an
incredible diversity of pigeons—science recognizes 309
species. Anatomical and behavioral adaptations have enabled
these birds to thrive in a wide range of habitats, from
tropical forests to deserts to tiny oceanic islands to
altitudes over 16,000 feet in the Himalayas. Only the Arctic
Circle and Antarctica have no pigeons.
Despite their success, many species have
suffered population declines and need protection. The pigeon
family is one of the most threatened in the world. Eleven
species have gone extinct, and one, the Socorro dove, native
solely to Socorro Island in the Mexican Pacific Ocean,
survives only in captivity. Fifty-eight pigeon species are
threatened with extinction, and conservationists consider 35
others vulnerable.
One of the most famous recent extinctions
is that of the passenger pigeon, which once ranged across
North America in the billions. Hunting of this pigeon as an
agricultural pest and the loss of its oak and chestnut food
trees with the settlement of the West sealed the fate of what
was probably the most abundant bird ever to live on Earth.
Fruit pigeons account for 22 of the
world’s threatened pigeon species. Among the fruit pigeons
that I recorded devouring figs were green pigeons, fruit
doves, and imperial pigeons, all of which flaunt gorgeous
plumage: typically greens above, with undersides and heads
decorated with stripes and spots. The rich hues of their
markings make these birds among the most colorful of all avian
life in the tropical forest. On Sulawesi, of the nine fruit
pigeons that live in the lowland forests, four are endemic
species and the rest endemic sub-species. Currently, none of
these pigeons are threatened with extinction, but because the
protected forest areas in which they survive are not secure,
their futures are far from assured.
I became aware of the fruit pigeons’
predicament from the very start of my project when I showed a
photograph of the endemic white-bellied imperial pigeon to
Bogani Wartabone’s head park ranger. Measuring 20 inches long,
this is the largest pigeon on Sulawesi, and its wu-wuu call is
so deep and booming, that I froze in alarm the first time I
heard it. I questioned the head ranger, “Ada burung ini
disini?”—Is this bird here? His reply: “Enak!”—Delicious!
His response worried me because fruit
pigeons play a critical role in dispersing the seeds of trees
and vines in the rain forest. By carrying seeds from intact
forest areas and depositing them in disturbed areas, they help
regenerate forest growth. The aim of my research was to
determine the abundance of each pigeon species and its
relative importance among other seed-dispersing birds in the
park, namely hornbills, parrots, and mynahs. This might sound
easy, but as fruit pigeons have mastered the art of
concealment, I had to base nearly all of my contacts with them
on bird calls. And most fruit pigeons have a number of
calls—all essentially variations and combinations of coo and
wu. This caused a number of headaches (quite literally), and
even more evenings spent trying to differentiate a wu coo from
a coo wu than I care to remember.
My research revealed that, in the lowland
rain forests of Sulawesi, fruit pigeons account for about 40
percent of all frugivorous birds, and they disperse the seeds
of at least 54 species of plants (further research will add
species to this list). This suggests that without fruit
pigeons, an awful lot of seeds would not be spread throughout
the forest.
Imperial pigeons and fruit doves are
particularly important seed-dispersers. They disseminate some
of the largest seeds, ones that few other bird species can
handle. Some of the seeds they manage to swallow are so big
that I found myself wincing in sympathy while I watched them
struggle to regurgitate. It must be like humans coughing up a
grapefruit!
It is thought that seasonal variability
in fruit production in lowland rain forest is a major reason
why frugivorous birds are especially at risk of extinction, in
addition to the threats posed by logging and fragmentation of
habitats. One main aim of my research was to compare the
feeding habits of rare fruit pigeons to those of more common
species. By identifying the distinctions, I hoped to pinpoint
which dietary traits correlate with rarity—and proneness to
extinction. Do rare species have greater specialization either
in the habitat they use, or the fruits they consume, or do
they suffer greater competition for their food resources?
Quite simply, I discovered that the
rarest frugivorous bird species include a higher proportion of
rare fruits in their diets. That means they may rely on larger
areas of forest to procure sufficient food, especially during
lean times. This ecological trait is clearly in conflict with
the widespread loss of forests throughout the tropics.
Additional research will be necessary to shed more light on
this relationship. Meanwhile, we need to monitor pigeons and
other fruit-eating birds that are at risk, lest any more go
the way of the passenger pigeon.
So, the next time a city pigeon harangues
you to share your sandwich, or worse still, poops on your
shoulder, try not to condemn all pigeon kind. Spare a thought
for its tropical cousins, the invaluable role they play in
maintaining the rain forest, and the threats that hang over
them.
Jonathan Walker was recently awarded a
doctorate of philosophy based on his two years of research in
Sulawesi. To read more about WCS’s work in Indonesia, log on
to www.wcs.org.
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