Photo Credit: Mike Lucibella

Adelie penguin populations, like this one at Cape Crozier, are the focus of ornithologist David Ainley and his team’s research.

Tag! You’re it!

New Tracking Devices Let Researchers Know What Penguins are Up To in the Winter

A number of Adelie penguins around the Ross Sea are sporting sophisticated new leg bands this year.

Photo Credit: Jean Pennycook

David Ainley and Jean Pennycook attach a new location tracking band to a penguin's leg.

A number of Adelie penguins around the Ross Sea are sporting sophisticated new leg bands this year.

Ornithologist David Ainley and his team attached new electronic tags to about 150 penguins to record where each penguin goes and how deeply it dives under water. The tagging project ties in with a broader effort that he’s been spearheading for 20 years, monitoring Adelie penguin populations and demographics around Ross Island.

Already the tagging has yielded a rather surprising scientific result: though there have been annual variations, overall the average annual extent of the sea ice around the Ross Sea has been increasing for the last 30 years. However, the number of penguins in the region haven’t been doing what Ainley predicted.

Photo Credit: Jean Pennycook

The new bands can tell researchers where a penguin travels using only the sun, and pressure sensors to see how deep they dive.

“We were expecting the population size to be decreasing because the sea ice is expanding, but it’s not,” Ainley said. “The population isn’t decreasing, in fact it’s increasing rather dramatically.”

He added that the penguins are thriving likely because too much commercial fishing has dramatically reduced the population of their biggest competitors, the Antarctic toothfish. Both Adelie penguins and the toothfish feast on the sardine-sized silverfish, but as the numbers of toothfish have declined, it’s made for easier pickings for the Adelies.

“Chicks raised with a high prevalence of fish in their diets become much more robust than those just raised on krill,” Ainley said.

Photo Credit: Mike Lucibella

Researcher Katie Dugger observes Adelie penguins at Cape Royds.

Ainley is the senior ecologist at a San Francisco Bay Area ecological consulting firm, H.T. Harvey and Associates. Every summer, he and his team set up camp near the Cape Crozier and Cape Royds penguin colonies on Ross Island to track how many there are and their nesting behavior.

With these new tracking leg bands, they hope to better understand what the penguins do and where they go over the long dark austral winter, when the team is back home and the penguins migrate out to sea. The project is supported by the National Science Foundation, which manages the U.S. Antarctic Program.

Previous research has shown that during the darkness of the months-long Antarctic winter, Adelie penguins leave their nests on dry land and swim north, past the Antarctic Circle, and spend the season on ice floes in the Ross Sea Gyre, a spiraling ocean current off the coast of West Antarctica.

“Like a big merry-go-round, they go around this big gyre in the winter time,” Ainley said. “Essentially they sit on ice floes most of the time, jump off every few hours, for a few hours a day they eat, then jump back on the ice.”

Photo Credit: Mike Lucibella

Analog penguin tags help researchers keep track of the overall penguin population and their behavior.

About the size of a high school graduation ring, the tags loop around the lower leg of the penguins so they don’t affect their mobility in the water. They’re similar to tags he and his team have used in the past to track their locations, but they also record information about how deep they dive.

Like their precursors, these new tags contain precise clocks and tiny light sensors. Using a modern version of age-old maritime techniques, it measures the position of the sun in the sky to calculate the bird’s location to within about 50 kilometers without needing a GPS.

“Just like in the old days of sailing ships with your sextant and all that kind of stuff, you can determine position based on day length and time of local noon relative to local Greenwich Time, and that gives you latitude and longitude,” Ainley said.

These new ones also have pressure sensors built into them so they can record how long and how deep a penguin dives under water. Next season, Ainley and his team will recover as many of the 155 deployed devices as they can, download the data and attach new devices to the same animals.

Photo Credit: Mike Lucibella

Researcher Emily Burke writes down a note after observing penguin chicks at Cape Crozier.

“The idea is to do it three years in a row and get a longitudinal study of having them on the same individual for three years, to see how it responds to differences in sea ice extent in the winter,” Ainley said.

Over the frigid winter months, the temperature around Antarctica drops to the point where the ocean itself starts to freeze. The ice builds up along the coastline and by the end of winter, extends out to sea for miles. How far out it reaches has a major impact on the penguin populations.

“We found in years where there’s really extensive sea ice in the Ross Sea region that four to five years later there would be a decrease in the colony size,” Ainley said. “What that’s saying is that survival of young birds is reduced in those years of very extensive sea ice.”

The new tags will be able to tell Ainley and his team more about how often the penguins are feeding on the silverfish. Krill live higher up in the water column than the silverfish, so when the penguins swim deeper to catch the fish, it’ll be recorded on their leg bands.

“This is an aspect of learning more about possible factors that affect population change,” Ainley said.

NSF-funded research in this story: David Ainley, H.T. Harvey & Associates, Award No. 1543541.