Plunging seabird populations has researchers turn to new types of analyses for answers
Posted August 1, 2008
Diminishing sea ice. Declining krill populations. Increasing snowfall and rain. Now it appears even ticks are harassing Adélie penguins along the rapidly warming Antarctic Peninsula.
Scientists are well aware that the cold and dry peninsula is turning into a warmer and wet subantarctic ecosystem. In turn, seabirds like Adélies and petrels are struggling to survive. But what is the chain of events? How do all of these pieces of the climate change puzzle fit together?
To blame it all on warming temperatures simplifies the problem, according to Ron Naveen, president of Oceanites Inc., a nonprofit science and educational foundation based in Maryland. Founded in 1987, Oceanites (pronounced “ocean-EYE-tees”) focuses much of its energy on the annual Antarctic Site Inventory.
The site inventory, launched in 1994 with a National Science Foundation (NSF) grant, includes more than 120 locations where Naveen and his team collect data about seabird populations and climatic conditions. Most of the work has been science by opportunity, with researchers hitchhiking aboard tourist ships.
Over the last five years, thanks to additional support from the NSF, Oceanites has also worked during the austral summer out of a field camp at Petermann Island, a 2-kilometer-long island home to one of the world’s southernmost colony of gentoo penguins, as well as a small group of Adélies.
More recently, Oceanites has partnered with William Fagan’s Conservation Biology, Community Ecology and Theoretical Ecology Lab at the University of Maryland. The lab integrates field research with theoretical models to address questions in community ecology and conservation biology.
Or as Naveen describes it: “We’ll take our data and put it into this statistical blender to explain precisely how climate change is causing certain effects in the peninsula. What’s the specific mechanism? It could be that it’s different on the east side than the west [of the peninsula]. It’s much more complicated a picture than we previously discovered.
“The hope here is to understand a little more directly … how change really occurs. What is the mechanism driving it? Is it predator populations, overfishing krill? Is it the weather?”
Heather Lynch, a post-doctoral researcher in the Fagan Lab, is heading up the statistical analysis. One of the tools she is using to model the data — Naveen’s statistical blender — is called hierarchical Bayesian analysis. The statistical model will help make sense of the temporal and spatial changes under way on the peninsula, as well as how variables like increased rainfall and diminishing sea ice relate to the penguin populations.
“The models are simply a way of getting around what is sort of a weak data problem,” Lynch explained. “We have relatively limited information from the Antarctic Site Inventory about a lot of sites. We’re trying to combine those data along with other available biological and physical data into a more comprehensive framework as to what’s going on peninsula-wide.
“We’re trying to collate a lot of information, which is observational in nature, so we don’t have a lot of control over it; but taken as a composite, we can put together a synthetic portrait of what’s going on,” she added.
Over the last 50 years, the peninsula has warmed an average of about 3 degrees Celsius, with winter temperatures about double that. The heat wave has pretty much cleared sea ice away during the summer around some parts of the region. In the winter, sea ice forms later in the season and retreats earlier.
That’s a problem because krill, shrimplike crustaceans central to the Adélie diet, need sea ice for winter grazing. The ice is also a key habitat for the penguins.
Throw into the mix heavier snowfall, which covers the ground and prevents the birds from making nests for laying eggs, and more precipitation falling as rain — something the penguin chicks are poorly adapted to handle.
“Rain kills,” Lynch said, because the fluffy down that allows the chicks to survive a sizeable snowstorm is useless when wet. “If they get three days of heavy rain, it’s all over. Because, if they get wet, they die of cold.”
Ticks from the genus Ixodes are also stressing penguins during their breeding season, according to Naveen. His team noted their presence a couple of years ago, and there are reports of ticks on penguins at Arthur Harbor, about 40 kilometers north of Petermann Island.
“It’s a terrible thing to see,” Naveen said. “The ticks get into the adult penguins’ feathers. The penguins start scratching. They stop paying attention to the eggs … We don’t have an answer to this question yet about the timing of it all.” In addition to being an annoyance, the ticks potentially carry disease.
All of those factors add up to steep declines in Adélie populations. In 1909, when French explorer Jean-Baptiste Charcot wintered on Petermann, the population of Adélies included 925 breeding pairs with only about 50 breeding pairs of gentoos, which belong to the same genus Pygoscelis.
“There’s been a total flip in population size since then over a century,” Naveen said. Adélies are down to fewer than 400 pairs, while gentoos are thriving, with more than 2,700 pairs. “This correlates quite specifically to temperature data in the region.”
Other researchers in the region are coming up with similar results for the different populations. Bill Fraser, president of the Montana-based nonprofit Polar Oceans Research Group, has studied seabirds in the region for more than 30 years.
Fraser said he and his team with the NSF-funded Palmer Long Term Ecological Research project recently confirmed the first extinction of an entire Adélie rookery at Litchfield Island. “By extinction, I mean that there are no more birds breeding on that island,” he told the Sun previously.
The gentoos, on the other hand, are enjoying the new subantarctic conditions that appear to be migrating south down the peninsula. A subantarctic species, gentoos are also able to dive deeper than their Adélie cousins and subsist on a more varied diet. They’re also bigger than Adélies — and apparently willing to bully where necessary.
“At Petermann, I’ve seen gentoos push Adélies off of nesting rocks and just take over,” Naveen said. “Size is a factor.”
The status of the third of the living Pygoscelis, or brush-tailed, penguins, is a “mixed bag,” according to Naveen. Chinstraps are doing well in some areas while declining in others, he said.
Naveen and the Fagan Lab just received another five-year grant award from NSF’s Office of Polar Programs to continue Antarctic Site Inventory data collection aboard the tourist vessels. New York-based Lindblad Expeditions has directly supported the project for nearly a decade.
“It’s quite an amazing cooperative effort,” Naveen said. “I’m not aware of anywhere else in the world where science and ecotourism cooperate so extensively.”
Jennifer Gregoire, a spokesperson for the Lindblad Expeditions, said the company is committed to conservation and environmental stewardship. It collaborates with a number of nonprofit groups, as well as the National Geographic Society, to promote eco-consciousness among the tourists it ferries around Antarctica and the rest of the world.
“The work with Oceanites is really great because our guests have the opportunity to interact with the researchers, learn about the project that they’re doing, and sometimes our guests are even able to participate in tasks like counting penguins,” she said.
The eco cruise company has 18 departures planned to Antarctica next season aboard two ships, the National Geographic Explorer and the National Geographic Endeavor. An estimated 34,000 tourists visited Antarctica during the 2007-08 austral summer. One of the uses of the data from the Antarctic Site Inventory is to study the effects of tourism on the continent.
But tourism is only one dimension to the Antarctic Site Inventory. Lynch is hopeful she’ll have the first iteration of a model completed in the next year or two that will give researchers a better idea of what makes some species like Adélies losers and gentoos winners in the climate change game.
“I think of it as being a process,” she said. “It will be a continuing conversation about what is going on in the peninsula.”
NSF-funded research in this story: Ron Naveen, Oceanites Inc., Award No. 0739430; William Fagan and Heather Lynch, University Of Maryland, Award No. 0739515; Bill Fraser, Polar Oceans Research Group, Award No. 0523261.
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