Penguin heaven: multi-decade science reveals secret lives of Adélies
Long-term Australian research shows that the breeding population of Adélie penguins in the Windmill Islands region of East Antarctica has increased sixfold over the past 60 years.
Seabird conservation ecologist with the Australian Antarctic Division, Dr Colin Southwell, said that the AAD’s research draws from generations of field biologists building one of the longest time-series of data available from Antarctica. Results are published in the ecological research journal Oecologia.
“We’ve used historical data that people collected back in the 1960s and 1980s and joined it with our current data,” Dr Southwell said.
“Over that time, the regional population has increased by a factor of six. It used to be about 30,000 breeding pairs, and now it’s almost 200,000 breeding pairs. That’s nearly half a million seabirds. It’s a very large population in the Windmill Islands, the third largest in East Antarctica.”
Dr Southwell describes many of the Windmill Islands near Casey research station as “penguin heaven”. One of them - Shirley Island - supports one of the largest breeding populations in the island group.
“Shirley Island is less than a square kilometre in area, but at the peak of the breeding season, there are currently nearly 40,000 breeding penguins,” he said.
“That’s a massive density. The density of penguins on that island at that time is higher than the human density of Manila, the most densely populated city of the world.”
To breed successfully, Adélie penguins need good nesting habitat on land, and good foraging habitat at sea, as parents must go out to sea to get food for their chicks.
“Good breeding habitat on land is free of ice and snow and not too steep. Not flat, because flat gets too wet. And with lots of pebbles, so they can build their nests,” said Dr Southwell.
“Good habitat in the ocean for foraging is an area with an intermediate amount of pack ice and not too much fast ice. Pack ice is a habitat for krill, which is their prey, and also provides a platform to rest on while feeding.”
An additional feature that makes Shirley Island particularly suitable is the lack of fast ice connected to land that enables the Adélie penguins to swim directly to their feeding grounds and not have to walk long distances over unbroken sheets of fast ice.
Population numbers are determined by arduous field work, with biologists directly counting penguins on land or with aerial photographic surveys from helicopters.
Seabird spy cameras
Over the last decade, Dr Southwell and his AAD colleagues have also established a network of remotely operating time-lapse cameras in the Windmill Island region and other parts of East Antarctica.
Throughout the year, no matter the weather, and at times when people can’t access the area, the cameras monitor the cycles of life in Adélie penguin colonies.
Honours student Madison McLatchie from the Institute for Marine and Antarctic Studies (IMAS) used photos from the automatic cameras for her thesis on ‘Environmental and Behavioural Drivers of Adélie Penguin Breeding Success in the Windmill Islands, East Antarctica.’
“I looked at how many chicks they were successfully raising from each nest. And I found that breeding success depended on how the male and the female maintained the nest throughout the season,” she said.
“If there was a high-quality nest of lots of rocks 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 rocks.”
Ten years of happy snaps
To gather 10 years of data on nest height and structure, Madison confesses to examining an “absurd amount” of photos that took five months to process.
“I looked at approximately 45,000! Because I looked at 10 photos per day for every season, over 10 seasons, from five different cameras at four sites,” 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 really helpful.”
“Basically the bigger the nest, the better. The higher the nest off the ground, the more likely the eggs and chicks are to be away from the snow cover and the moisture on the ground.”
Finding that nest structure has a major impact on chick survival is a relatively new discovery.
“We weren’t expecting that that was going to be the main driver of their breeding success. We were expecting maybe an environmental variable, like snow cover or even ground moisture, to have more of an influence on breeding success,” Ms McLatchie said.
Dr Southwell said that the regional population growth in the Windmill Islands is one of the highest recorded for Adélie penguins, and while some penguin populations had gone “gangbusters”, the overall rate of growth has slowed in recent decades.
“We’d like to know why, and that’s some of the investigations we’re doing now. To understand that, we need to compare the habitat in the Windmill Islands, with habitats in other regions that might be increasing more slowly.”
“What we’ve found is that the populations that are stable, don’t have much breeding habitat left. So, they’ve been able expand their population in previous years, and virtually filled that habitat so they can’t grow any more. We found that the populations that have been increasing quickly have a lot of habitat left. So, breeding habitat isn’t constraining their growth,” he said.
“We’ve done the same for their foraging habitat – the penguins leave their breeding habitat and forage out at sea, out to a couple of hundred kilometres. The populations that are stable are generally competing with many more other penguins from neighbouring colonies, than the populations that are increasing.”
While Madison is yet to meet an Adélie penguin ‘in person’, she feels an intimate connection with the Windmill Island colonies.
“The results of my thesis are really important for the conservation of Adélie penguins, especially with global issues like climate change and over-fishing, because we’re able to see what might happen to their populations into the future,” she said.
“If temperatures in Antarctica get warmer in the future, there’s going to be more snow melt, and this could negatively influence breeding success. Even with a higher nest, if there’s heaps of water, breeding success could be negatively impacted.”
For Dr Southwell and his team, the long-term focus on Adélie penguins reveals a bigger picture of how competition between species in the Antarctic food chain shapes the broader ecosystem.
“By studying Adélie penguins which are quite accessible on land when they breed, we can gain insights into what’s happening in the ecosystem in the ocean, how physical factors like sea ice influence species at sea, and understand how different species interact with each other.”
Information on Adélie 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 the protection of marine areas.