Cosmos
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By Cosmos
Australian scientists are monitoring massive populations of Adélie penguins along the East Antarctic coastline in an attempt to understand the cause of recent declines in some breeding areas and whether there’s regional variation amongst other colonies.
The most recent estimates say there are 14-16 million Adélie penguins — including the breeder and younger non-breeding populations — living along almost the entire coastline of Antarctica. Adélies are the sea birds which gave us the phrase: “Penguin suit.”
They are about 70cm tall when grown and weight about 6kg.
Long-term monitoring of a significant Adélie population near Mawson Station has shown a 43% decline in the breeding colony over the past decade.
Australian Antarctic Division seabird ecologists, Dr Louise Emmerson and Dr Colin Southwell, have been monitoring Adélies for more than 20 years, and recently reported a loss of some 154,000 breeding birds, across 52 islands along the 100 km of coastline.
The research is published in Global Change Biology.
This contrasts with other populations in East Antarctica, which have had long-term stable or increasing population trends.
The researchers say the rate of decline is similar to that in Adélie penguin populations on the Antarctic Peninsula, which are subject to pressures from fisheries, climate change and human activity.
However, the decline in the Mawson population is thought to have been triggered by changed environmental conditions, exacerbated by internal feedback processes within the population, rather than direct human-related pressures.
“We think this population decline was initially triggered by five years of extensive summer sea ice adjacent to the colony in the mid-2000s, which hampered access to the adults’ foraging areas and saw virtually no chicks survive,” Emmerson said.
According to Emmerson, the theory is that the smaller a population becomes, the harder it may be for individuals to survive, due to an increased risk from predators, or because smaller groups are not as good at navigating, foraging and locating prey.
Emmerson says this is especially important for young fledglings with limited life experience.
Adélie penguin fledglings are totally clueless
“Adélie penguin fledglings are literally thrown in the deep end at about two months of age, when they leave the colony and enter the Southern Ocean for the first time, without parental supervision,” she says.
“I remember watching fledglings enter the water for the first time and they did this strange kind of breaststroke, as though they were trying to use their flippers to stand up. It was a completely new experience for them,” Emmerson said.
“When they first enter the water they don’t know how to swim, they have no predator avoidance behaviour, so they are vulnerable to being eaten by leopard seals, and they’re not efficient at catching prey. They’re totally clueless about their marine environment, and because there are no adults to help them, they have to learn quickly or they don’t survive.
“So while we don’t know exactly what’s driving the decline in fledgling survival in the Mawson area, the fact that there are less of them may compromise their chances of survival.”
Emmerson says one of her concerns with this particular population decline is that it’s driven by failed breeding success and a reduction in survival of the fledglings, and the interaction between the two as the population declines: “…so those younger cohorts that would normally come through to be part of that breeding population – they’re not there, they’re absent, and obviously that will mean that flow on effect in the breeding population which then begins to decline.”
Read more: How do you track a penguin?
Emmerson says a total population survey might need to be done again given the recent population decline.
Southwell said the finding of variation in population rates across the region is focussing their minds on the complexity of population processes and how difficult it is to predict ahead in time.
The scientists are not connecting global warming for the population declines, although they say it might be having an impact that’s not been measured yet, and could be responsible for the change in sea-ice conditions in this area.
“It’s difficult in such a remote place to understand what’s even going on now, and to predict the future is even more difficult, and that’s the challenge for us, to try and forecast the future as best as possible with the information we have and improve that information over time.”
Southwell says the research they are undertaking tries to look at the entire Adélie picture across East Antarctica. “This population on Mac.Robertson Land near Mawson station is one of several very large populations across East Antarctica and we’ve been trying to understand what’s going on with all of them.
“The Windmill Island population increased six fold in six decades and is still increasing, but we are seeing signs now that population growth is starting to slow; they’re still increasing but at a slowing rate.
“What we think is going on there is they’re starting to hit the limit of certain resources that they need, for example, the amount of space they have on ice free land for breeding, the amount of food they have which can become limited through competition with their own. So you’ve got all of these penguins breeding on particular islands and their foraging zones are overlapping, so they are actually competing with each other for food.
“That would be expected. No population can keep on growing forever.”
Emmerson says the research shows how rapidly a population can go from doing ok, to really not doing ok. “I think that is a problem. Can these birds adapt to a changing environment?”
Southwell says one of the great challenges is to “tease apart all those potential influences.”
“It’s not just climate change. It’s not just human activity; there are fisheries happening as well. When all these activities are happening in the same area it makes it very difficult as a scientist to put your hand on your heart and say we know exactly which impact is going on here.
“And it takes a lot of planning and thinking to establish the science and design of the monitoring programs to give you the best chance of attributing cause.”
“We do have to make sure we’ve got the right monitoring, so that we can detect early warning signals that anything’s going wrong, and even though it is a large population we want it to stay healthy.
“We are concerned about the population decline that has occurred in this area.”