(WHOI / 28-09-09) Biologists used mathematical models to predict the effect on penguins of climate change and the resulting loss of sea ice. The research indicates that if climate change continues to melt sea ice at predicted rates, the median population size of a large emperor penguin colony in Terre Adelie, Antarctica, likely will shrink from its present size of 3,000 to only 400 breeding pairs by the end of the century.

Emperor penguins, which delighted audiences of the Academy Award-winning documentary March of the Penguins, could be sliding on the path toward extinction —the victims of climate change.

The key threat to the penguins is diminishing sea ice, an essential platform on which the tall, tuxedoed birds breed, feed, and molt. The ice also serves as a grazing ground for krill, tiny crustaceans that thrive on algae growing on the underside of the ice. Krill, in turn, provide food for fish, seals, whales, and penguins.

Stephanie Jenouvrier and Hal Caswell, biologists at Woods Hole Oceanographic Institution (WHOI), developed mathematical models that project the penguins’ population growth and decline based on observations of the birds’ mating, breeding, and feeding behaviors and birth and mortality rates. The models used data collected over 43 years by French scientists studying the large emperor penguin colony in Terre Adelie, Antarctica.

Jenouvrier and Caswell coupled their population dynamics models with projections of Antarctic climate change and resulting loss of sea ice, working with scientists from the National Center for Atmospheric Research and the National Snow and Ice Data Center and from Expeditions Polaires Francaises and Institut Paul Emile Victor in France. Their results predicted what would happen to the Emperor penguin population under different climate scenarios.

The study, published this year, in Proceedings of the National Academy of Sciences, showed that if climate change continues to melt sea ice at the rates published in the latest Intergovernmental Panel on Climate Change reports, the median population size of the Terre Adelie penguin colony likely would shrink from its present size of 3,000 to only 400 breeding pairs by the end of the century.

What’s more, the researchers calculated a 40 to 80 percent probability that the population would drastically decline (by 95 percent or more) and threaten it with extinction.

In the 1970s, reduced sea ice conditions led to a 50-percent population decline in the Terre Adelie population. But how sea ice changes affect the penguins is complex and still not fully understood. Nor is it known how climate changes would affect other emperor penguin populations throughout Antarctica.

“Unlike some other Antarctic bird species that have altered their life cycles to changing conditions, penguins are long-lived, so they adapt slowly,” Jenouvrier said. “This is a problem because the climate is changing very fast.”