Posted February 18, 2011
They’ve observed the large-scale changes over the summer seasons that have seen some colonies balloon to historic numbers, while at least one has plummeted to a near-record low. [See previous article: After the icebergs.] Now the scientists are focusing on why some individuals within the colonies are more successful than others in terms of foraging and breeding success.
Understanding the factors that determine which birds are better suited for the Darwinian dance of life can help the researchers predict how the penguins may fare in the future as climate change re-writes the script for survival.
“We’re getting a much better feeling with how individuals can cope with different scenarios,” said Grant Ballard , his face burnished nearly scarlet from the sun and wind of an Antarctic summer at Cape Crozier on Ross Island, home to one of the largest Adélie penguin colonies in the world.
Ballard and his co-principal investigators, David Ainley , an ecologist with H.T. Harvey and Associates in California, and Katie Dugger at Oregon State University , are at the start of a new five-year grant from the National Science Foundation that takes a bottom-up approach, focusing on individual capability, to learn how large populations will evolve and adapt over time.
Ainley said only about 20 percent of a given colony sustains the population consistently. More birds will breed successfully in “easy” years — when the journey across the sea ice from the rocky islands where the penguins nest to the open ocean where they forage is short.
But in tougher years, when the sea ice extends so far that the energy required to forage and feed their young causes many to fail, a special “breed” of penguin somehow manages to fledge their chicks to adulthood.
“We found these super-breeders are much better foragers. They dive deeper; they have a shorter recovery period at the surface between dives. They bring back more food,” said Ainley, who first worked with the Ross Sea penguins in the 1970s as a PhD student.
Is it just a matter of genetics — a matter of being faster and stronger? Or does age and experience have anything to do with success?
It’s probably both, according to Ballard. The pattern the researchers have detected so far suggests that age and experience count, but older doesn’t necessarily equate to breeding success.
“There does seem to be variability at the individual level,” said Ballard, a staff scientist at PRBO Conservation Science in California.
For each of the last 15 summers at Cape Crozier, the penguin team has banded 1,000 new adults, so the researchers have a large pool of known-age birds that they track. Most nest at a site called Area M, home to about 20,000 of the estimated 230,000 breeding pairs spread across about 5 kilometers of the moraines on the lower slopes of Mount Terror.
Still, not all the birds cooperate, so Ballard and his colleagues hike the length and breadth of the colony at least once a week to locate the stragglers. They randomly select “super-breeders” and their ordinary cohorts for putting on time-depth recorders.
The compact instruments, painlessly taped on the lower back of the animal, provide data on how deep and how long a penguin dives on a foraging trip. A simple V-shape dive means the critter likely came up with an empty stomach. A distinctive wiggle at the bottom of the dive signals success.
“There are some individuals that always have the biggest chicks, and they’re always in the colony,” Ballard said. In other words, the super-breeders get in, get out and get back to the colony more efficiently. That means not only more food, more often for its chicks, but more protection against predatorial skuas because super-breeders spend less time away from the nest.
Eventually, the team wants to determine to what extent the abilities of super-breeders are passed on to succeeding generations. Is it hereditary? Or are there enough “easy” years when the gene pool becomes flooded, diluted by the genes of the other 80 percent?
“There’s still a huge amount of mystery when it comes down to it,” Ballard said.
Dugger noted that one can’t be into instant gratification in this business of demographic research. “We get one data point each year with a huge amount of effort,” she said.
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 .