One, Two, 3.79 million: How Many Penguins Are There?
A recent study found that Adélie Penguin populations are increasing, but that doesn’t mean the birds aren’t still threatened by climate change.
If Adélie Penguins would just sit still, they’d be easier to count. Scientists had only a rough idea of their overall numbers until last month, when results of the first Antarctica-wide Adélie census were reported in The Auk, the journal of the American Ornithologists’ Union. Apparently, Antarctica has more penguins than we thought: The researchers found 53 percent more Adélies than previously estimated, with the help of satellite imagery able to spy on remote colonies. The finding, which totals Adélies at 3.79 million breeding pairs, is welcome news, though Antarctica’s most charismatic birds still face an uncertain future.
Of Earth’s 17 (or so) penguin species, only two are restricted to Antarctica. The Emperor Penguin (star of Happy Feet and March of the Penguins) is the world’s largest, about four feet tall with a gorgeous swoosh of yellow behind each cheek. Emperors nest on ice, lay one egg in winter, and live up to 50 years. Adélie Penguins overlap with Emperors for much of their range but have very different features and habits: They are half as tall, lack color on their black-and-white tuxedo, nest on land, lay two eggs in summer, and live up to 20 years.
Emperors are regal and deliberate in manner. Adélies are mischievous, energetic, competent, and curious, and they have little fear of humans. I know first-hand, because I spent three months studying a colony of a quarter-million Adélies at Antarctica’s Cape Crozier a few years ago, and each year I visit lots of Adélies during expedition cruises. I find the Adélies utterly captivating, especially when they waddle up to me, wide-eyed, to inspect my shoelaces.
A New Kind of Census
Researchers Heather Lynch and Michelle LaRue, working from Stony Brook University and the University of Minnesota, used Google Earth-type satellite photographs to zoom in on penguin colonies around Antarctica’s coastlines. From space, the colonies show up in poop: Blotchy brown stains of guano stand out against rock and ice. By calculating the density of nesting penguins through on-the-ground counts, Lynch and LaRue were able to infer, with fine accuracy, the number of Adélies each satellite image represented.
This marks the first time anyone has counted the world’s Adélies by satellite, though LaRue worked on a similar 2012 study with Emperor Penguins (which nearly doubled the known Emperor population). The authors found several new Adélie breeding sites and conducted careful censuses of established colonies. The resulting figure of 3.79 million pairs is half again higher than the last worldwide estimate, published in 1993.
What’s in a Number?
Although much of the 53 percent difference reflects improved counting techniques, Lynch and LaRue report that Adélie Penguin populations are generally going up. Nearly a third of the difference, they say, can be attributed to real increases at known colonies.
Population trends are more pronounced on a regional scale. The biggest Adélie Penguin colonies, in the Ross Sea area of Antarctica (where significant sea ice remains), have been growing steadily for several decades, while those on the western Antarctic Peninsula (where sea ice has declined in recent years) are now crashing. So far, the Ross Sea increases have been enough to offset declines elsewhere. But while this is good news, it doesn’t mean that climate change isn’t a problem for the birds.
Peering Into the Future
Adélies spend most of their lives at sea and rely on sea ice as a platform for hunting krill, a small, shrimp-like crustacean (krill also rely on sea ice to feed, as they consume algae that clings to floating ice). Because of this double-pronged dependence on sea ice, Adélie Penguins are indicators of their Antarctic environment—a “canary in the coal mine” for climate change. As far as scientists can tell, krill and sea ice are the two most important factors affecting Adélie Penguin populations—and they’re each seriously affected by climate change as the earth warms and sea ice melts.
Some scientists worry that climate change may shift the balance for penguins in coming decades. In 2012, the IUCN Red List uplisted both Adélie and Emperor penguins from “Least Concern” to “Near Threatened,” citing an expected “moderately rapid population decline over the next three generations owing to the effects of projected climate change.” A 2010 paper by Adélie expert David Ainley and colleagues warned that, if Earth’s temperature reaches two degrees Celsius above pre-industrial levels (projected, in the same paper, to occur between 2025 and 2052), Emperor and Adélie colonies north of 70 degrees south would decline or disappear, affecting 40 percent and 70 percent of their respective breeding populations.
We don’t know exactly how Antarctica’s penguins will react to a shifting climate. At least, with this latest satellite census of Adélie Penguins, we now have a yardstick against which the future can be measured.