By counting penguins based on satellite imagery of their guano -- that would be poop -- two researchers, one from Stony Brook University, have determined 53 percent more Adélie penguins are living in Antarctica than previously estimated.
While much focus has been on the seabirds' decline on the Antarctic Peninsula, in other parts of the continent "Adélies are not only increasing, but those increases appear to be offsetting the losses elsewhere," said Heather Lynch, quantitative ecologist and assistant professor at Stony Brook University.
Lynch is lead author of "First Global Census of the Adélie Penguin," an article posted last week on "The Auk: Ornithological Advances," published by the American Ornithologists' Union.
The 10-month study, which scrutinized thousands of high-resolution images of coastal breeding grounds and included some ground counts, found 17 previously unknown colonies and growth or probable growth in 49 known colonies.
The study also confirmed the decline in the species' numbers on the peninsula, which juts out toward the tip of South America. That's where the authors say "drastically decreasing sea ice" has led to fewer krill, the shrimp-like crustaceans that are a favored meal for the Adélie, considered a bellwether creature in monitoring and understanding climate change.
In all, an estimated 3.79 million penguin pairs in 251 breeding populations were identified along the coasts of Antarctica and sub-Antarctic islands, the only place on earth where Adélie are found in the wild, Lynch said.
The census provides a baseline against which to assess future change, data that officials can use in determining fishing limits and protected marine areas, as well as insight into the ability of Adélies, known to return faithfully to the same areas, "to colonize new breeding territories," the article said.
Noted for the small white rings encircling their eyes, Adélies breed on exposed rock along the coast where they have easy access to open water and their food supply, according to Antarctica.gov.au. Discovered in 1840 by a French expedition, they were named for the lead explorer's wife, the site says.
One hypothesis for the higher-than-expected head count, the authors say, involves increased commercial fishing of Antarctic toothfish, a competing predator for silverfish, which is another Adélie meal of choice.
The researchers' approach is "cutting edge," using the same technology to estimate penguin numbers that's used by law enforcement to zoom in on car license plates, said David Ainley, a marine ecologist, consultant and co-author of "The Adélie Penguin: Bellwether of Climate Change."
Scientists can now build on this research, as well as "derive a regional picture of trends" instead of projecting from isolated colonies that a few researchers have tracked and studied, said Ainley, of the San Francisco Bay Area, who was not involved with the project. Ironically, though the Antarctic is one of the most difficult places on earth in which to do in-person research, its desolation and lack of trees, vegetation and structures make it ideal for satellite observation because nothing obstructs the view, said Lynch's collaborator, Michelle LaRue, conservation biologist and research associate at the University of Minnesota.
The two reviewed commercial satellite imagery, mostly from the last three years, from December and January, which is peak incubation time for penguin eggs. From analyzing 5,500 kilometers (3,400 miles) worth of coastline, "meter by meter by meter," they identified areas of "guano staining" that were converted to an estimated number of penguin pairs, the report said, as the seabirds' density at breeding time is fairly fixed and well-known.
Lynch, 35, who has a background in physics, sees her role as that of "a detective" using mathematical models to determine "some larger picture" about the populations.
The best part of her job is not observing close up the sleek swimming, land waddling creatures, she said, but is "sitting in front of my computer and writing computer code."LaRue, 31, who conducted a similar census on Emperor penguins, says she and Lynch make a complementary team. When LaRue sees the seabirds up-close and personal, she says she's "super-fascinated" with their behavior, while Lynch might say something akin to, "Look at all those data points."