Return to boom times?
Cape Royds penguin colony shows signs of bouncing back
Posted May 24, 2013
The Adélie penguin boomtown known as Cape Royds went bust in the 2000s. Now there are signs that a recovery is under way.
The volcanic rocky headland on Ross Island has always been a sleepy place compared to the other Adélie penguin colonies in the region. It represents the farthest south Adélies have dared to set up breeding grounds.
By the turn of the century, about 4,200 breeding pairs made nests at Cape Royds. Then came the march of the icebergs, big tabular slabs of ice that blocked McMurdo Sound from the rest of the Ross Sea . Sea ice increased dramatically in the region. Royds became even more isolated, and life untenable except for the most hardy of the flightless seabirds.
Ainley is the principal investigator for a long-term project trying to understand factors behind the population dynamics and trends at Royds and other colonies in the Ross Sea region.
Every day or two he leaves his field camp — a semi-permanent structure that serves as kitchen, lounge and office, along with a few expedition tents — and walks among the squawking birds. Binoculars and yellow-covered notebook in hand, he records his observations, looking for birds that he, and others of his team have banded over the years.
Ainley’s research into penguin ecology and population dynamics goes back to the 1970s. Yet Antarctica’s iconic bird still surprises him.
“They’re kind of perplexing,” he said, a wisp of a grin under his white mustache.
Take the penguin diaspora and recent homecoming of the young adults that had been out to sea in recent years.
Ainley had expected it would take time before the colony could recover its numbers, which had dropped to about 1,400 breeding pairs by the summer of 2010-11. Even then, young birds around age 4 were starting to trickle back. [See previous article — Population pressures: Changes in Ross Sea environment, fishery cause demographic shift in species.]
This season, the number of known-age birds banded by the scientists doubled, from 35 to 72 nests. In the worst years, barely 20 nests could be found amongst the crowd. Still, many didn’t breed, though they showed up at their usual guano-stained spots, going through the motion of playing house.
Photo Credit: Peter Rejcek
Adult Adélie penguins care for a chick, while a second begins to break free of an egg.
“As they get older, they spend more and more time at the colony,” Ainley said.
One significant change that appears to be at play: The average breeding age of the Ross Island penguins has crept up from between ages 4 and 5 to ages 6 and 7.
Ainley and co-principal investigators Katie Dugger and Grant Ballard believe that may be due to the increasing sea ice in the region. While the icebergs may be long gone, change in climate is increasing the extent and duration of sea ice in the Ross Sea sector of the Southern Ocean.
That takes the penguins farther and farther away in winter as they ride a huge sea ice merry-go-round. The researchers learned this by attaching geo-locator tags to birds that had just fledged chicks in several seasons. Being farther away in spring means later arrival — especially for young birds that act like tardy teenagers anyway — to the extent that many don’t arrive in time to lay eggs.
However, the populations at most of the other Ross Sea colonies under study are increasing — a puzzle that Ainley blames on a commercial fishery that is removing a primary competitor from the ocean: the Antarctic toothfish.
Photo Credit: Peter Rejcek
Adelie penguins on their nests at Cape Royds. Mount Erebus, an active volcano, is in the background.
A long-lived species that can weigh in excess of 100 kilograms, the Antarctic toothfish is sold as Chilean sea bass at restaurants and supermarkets. One of its primary prey is Antarctic silverfish, Pleuragramma antarcticum. The penguins also favor this herring-sized fish, which may be more plentiful with fewer top predators around thanks to the dozen fishing vessels that ply the Ross Sea every summer.
“That’s why we think the penguin population is increasing. …Things are changing, and it doesn’t appear to be because of climate,” said Ainley, who has advocated creating a marine protected area for the Ross Sea. Previous analyses showed that colony sizes drop when there is very extensive winter sea ice.
Proposals among the international community have fallen short of what Ainley would like to see happen. A New Zealand-based documentary called The Last Ocean follows his and others’ efforts to conserve the Ross Sea ecosystem.
“It’s not too late if they stop or seriously slow the fishing right now,” he said. “It would still be less impacted than anywhere else. It would take 20 years to recover, if it did recover, given that the environment is changing.”
NSF-funded research in this story: David Ainley, H.T. Harvey and Associates, Award No. 0944411 ; Grant Ballard, PRBO, Award No. 0944141 ; and Katie Dugger, Oregon State University, Award No. 0944358 .