Long-term Australian research shows that the breeding population of Adelie penguins in the Windmill Islands region of East Antarctica has increased sixfold over the past 60 years.
Dr. Colin Southwell, seabird conservation ecologist with the Australian Antarctic Division, said the Australian Antarctic Division’s research draws on generations of field biologists who have produced one of the longest time series of data available from Antarctica. The results were published in the ecological research journal Oecologia .
“We used historical data that researchers collected in the 1960s and 1980s and linked it to our current data,” Dr. Southwell said.
“During this time, the regional population has increased by a factor of six. There used to be about 30,000 breeding pairs, and now there are almost 200,000 breeding pairs. That’s almost half a million seabirds. The population in the Windmill Islands is very large, it’s the third largest in East Antarctica.”
Dr. Southwell describes many of the Windmill Islands near the Casey Research Station as “penguin heaven.” In the process, Shirley Island hosts one of the largest breeding populations in the archipelago.
“Shirley Island has an area of less than one square kilometer, but at the peak of the breeding season, nearly 40,000 penguins are currently breeding,” he said.
“That’s a tremendous density. The penguin density on this island at this time is higher than the human density of Manila, the most densely populated city in the world.”
To breed successfully, Adelie penguins need a good nesting site on land and a good food supply in the ocean to provide food for their chicks.
“Good breeding habitats on land are free of ice and snow and not too steep. To keep the nests from getting wet, the substrate must not be flat and must be covered with lots of pebbles so they can build their nests,” Dr. Southwell said.
“A good ocean foraging habitat is an area with a moderate amount of pack ice and not too much fast ice. Pack ice is a habitat for krill, which is their prey. Pack ice also provides a platform for them to rest on while feeding.”
Another feature that makes Shirley Island particularly suitable is the absence of fast ice connected to the land, which allows Adelie penguins to swim directly to their feeding grounds rather than having to walk long distances over unbroken sheets of fast ice.
Population numbers are determined through painstaking fieldwork, with biologists counting penguins directly on land or with aerial photographic surveys from helicopters.
Seabird spy cameras
Over the past decade, Dr. Southwell and his AAD colleagues have also established a network of remote time-lapse cameras in the Windmill Island region and other parts of East Antarctica.
Throughout the year, in all weather conditions and during times when humans cannot enter the area, the cameras monitor the life cycles in the Adelie penguin colony.
Madison McLatchie of the Institute for Marine and Antarctic Studies (IMAS) used photos from the automated cameras for her senior thesis on “Environmental and Behavioral Drivers of Adélie Penguin Breeding Success in the Windmill Islands, East Antarctica.”
“I looked at how many chicks they successfully raised from each nest. And I found that breeding success depended on how the male and female maintained the nest throughout the season,” she said.
“If there was a high quality nest with lots of stones built high off the ground, they were more likely to have one or two chicks compared to a nest where the chick was directly on the ground with minimal stones.”
Ten years of monitoring
To process those of more than 10 years of observations about the height of nests and their structure, Madison admits to examining an “absurd amount” of photos that took five months to process.
“I looked at about 45,000! Because I looked at 10 photos a day for each season over 10 seasons from five different cameras in four locations,” she said.
“The cameras take a photo of the colony as a whole, but we were able to zoom in on individual nests, which was very helpful.”
“Basically, the bigger the nest, the better. The higher the nest is above the ground, the more likely the eggs and chicks will be away from the snowpack and moisture on the ground.”
The discovery that nest structure has a major impact on chick survival is a relatively recent discovery.
“We didn’t expect that to be the main reason for their breeding success. We expected that maybe an environmental variable like snowpack or even soil moisture would have a bigger impact on breeding success,” Madison McLatchie said.
Dr. Southwell explained that regional population growth in the Windmill Islands is one of the highest for Adelie penguins, yet the overall growth rate has slowed in recent decades.
“We’d like to know why that is. To understand, we need to compare the habitat on the Windmill Islands with habitats in other regions.”
“What we’ve found is that the populations that are stable don’t have much breeding habitat left. So they’ve been able to increase their population over the past few years and they’ve basically filled up that habitat, so they can’t grow any more. We found that the populations that have increased rapidly still had a lot of habitat left,” he said.
“We did the same for their feeding grounds. The penguins leave their breeding grounds and forage out to sea as far as a few hundred kilometers. The stable populations generally compete with many more other penguins from neighboring colonies than the populations that are growing.”
While Madison has yet to meet an Adelie penguin “in person,” she feels a close connection to the Windmill Island colonies.
“The results of my doctoral research are really important for the conservation of Adelie penguins, especially with global issues like climate change and overfishing, because we can see what might happen to their populations in the future,” she said.
“If Antarctic temperatures get warmer in the future, there will be more snowmelt, which could negatively affect breeding success. Even with a taller nest, breeding success could be negatively impacted if water pools.”
For Dr. Southwell and his team, the long-term focus on Adelie penguins reveals a bigger picture of how competition between species in the Antarctic food chain shapes the broader ecosystem.
“By studying Adelie penguins, which are readily accessible while breeding on land, we can gain insight into the ocean ecosystem, how physical factors like sea ice affect species in the ocean, and understand how different species interact with each other.”
Information on Adelie penguins from the Australian monitoring program is used by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) in managing krill fisheries and considering marine conservation.
Report from: Australian Antarctic Division
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