For Penguins, a Satellite Census
Biologists Count Hard-to-Find Birds With Photos Supplied by
In the first complete census of these well-known birds, the
"You can count individual birds," said Dr. Trathan, a penguin ecologist at the British Antarctic Survey, who is part of an international census team.
Their penguin census, which will be completed later this year, is the latest application of satellite mapping techniques that are transforming perceptions of Antarctica, where millions of square miles of ice blend into a wilderness of white, and only penguins are truly at home. In many ways, this shifting snowscape is as uncharted as the day explorers first sighted its mainland almost 200 years ago.
"Until last year, we had better maps of Mars than of Antarctica," said Paul Morin, director of the
With the newest high-resolution imagery, researchers can detect anything on the continent larger than an end table. At that scale, a four-foot-tall, 90-pound emperor penguin is just large enough to show up in a single pixel. Dressed by nature in darkly formal feather-wear, an emperor penguin stands out in high contrast against the ice, even when viewed by a camera moving at four miles a second in an orbit 423 miles overhead.
Still, the emperor penguins complicate the count by huddling together for warmth. On an especially cold day, as many as 10 of them can cram together on a square meter of ice—a space slightly larger than a single pixel. "If you have so many pixels of penguins," said mapping expert Peter Fretwell at the British Antarctic Survey, "you have to decide how many penguins per pixel." Wildlife biologists estimate the count will turn up between 200,000 and 400,000 breeding pairs.
Living across the continent's 5.4 million square miles of polar ice, the emperor penguins are a bellwether that can help researchers detect subtle changes in climate and ocean conditions affecting all of Antarctica. Other penguin species wax and wane in response to changing regional winds, temperature trends and commercial fishing. But so far, no one knows how emperor penguins have responded to the changes, because there has been no easy way to find them all.
"Emperors are a really tricky species to get a handle on," said Dr. Trathan. "At the moment, nobody really knows how threatened emperor penguins really are."
It's no wonder. The birds make themselves at home in two of Earth's most inaccessible environments. No other bird dives deeper underwater, as far as 1,500 feet. No other creature breeds on the sea ice during Antarctica's winter darkness, when temperatures drop to 80 degrees below zero and winds top 100 mph.
For years, field biologists based here at the U.S. McMurdo Station have tracked meandering emperors, bobbing like off-balance bowling pins, as they slip, slide and belly-flop over ridges of wind-rippled snow.
Penguins Under Pressure
They have stood on stepladders to count the birds in congested formations, and hung cameras from helium-filled balloons to record their numbers more reliably.
They have bugged penguins with radio transmitters and shadowed them by jet with airborne infrared sensors that could detect a birds'
The new census is not the first time penguin watchers have tried satellites. By chance, researchers last year discovered they could detect vast stains of penguin excrement on the ice using older low-resolution satellite images. That revealed the locations of 38 emperor colonies, 10 of them never seen before, Dr. Trathan and his colleagues reported last June in the journal Global Ecology and Biogeography.
Still, they couldn't actually see any penguins until they gained access to the newest images, which the
Scientists hope the newest images will allow them to study emperor penguins without disturbing them—and without leaving their home laboratories.
"If you can do it from space," said Dr. Trathan, "you can do it from your desk."
Write to Robert Lee Hotz at firstname.lastname@example.org