Introduction
Reports suggest that climate change is putting some penguin species in peril. Scientists at British Antarctic Survey investigating long-term changes in penguin populations report what’s happening to these iconic birds.
Are penguin populations really declining?
Some species and populations are but others are not – it varies among species and locations. Long-term monitoring of penguin populations in the Scotia Sea region reveals a complex picture. In the last 30 years, populations of Adélie penguins on the South Orkney Islands have fluctuated and are currently in decline, while chinstrap populations have decreased significantly and gentoo numbers have risen. On South Georgia, the population of macaroni penguins has declined from 2.5 million breeding pairs in the 1970s to just about 1 million today. King penguins have increased from a few hundred in the 1920s to over 450,000 today. Further south, emperor penguins, which breed on sea ice surrounding continental Antarctica, have also experienced a decline in numbers during recent decades – by up to 50% in places and one of the most northerly colonies of emperors on a small offshore island close to the Antarctic Peninsula is now thought to have disappeared completely.
Why is there such a difference between species?
This is a key issue that British Antarctic Survey (BAS) scientists are currently working on. Unravelling the reasons behind the changing populations of penguins in the subantarctic and Antarctic is complex and involves a number of factors. Food supply and available nest sites are likely to be responsible for most of the changes observed in penguin populations. BAS and US scientists have discovered that sea ice plays a major role in declining penguin numbers. Krill, the small shrimp-like crustacean that is the main food source for many species of penguins, seals and whales, spend their early life grazing phytoplankton from the underside of winter sea ice. The observed Adélie and chinstrap population changes in the Western Antarctic Peninsula are linked to reductions in sea ice and the associated changes in food supply.
So, is climate change affecting penguin populations?
The rapid climate warming on the western Antarctic Peninsula has reduced sea-ice cover by around 40% in the last 30 years, which impacts the success of the ‘krill nurseries’. Krill abundance across the Scotia Sea has undergone a long-term decline, particularly in the north of its range around South Georgia. This is likely to have contributed to the decline of macaroni, Adelie and chinstrap penguins in the region. The decline in some emperor colonies is likely to be explained by loss of sea ice as this species depends on sea ice as a nesting platform and foraging habitat. Gentoo penguins, however, have increased their numbers and range in the Antarctic Peninsula as reductions in sea ice there have improved habitat quality for this ice-intolerant species. Similarly, Adélie colonies in East Antarctica are mostly increasing with climate change due to greater availability of ice free land as nesting habitat, and reduction in dense sea ice cover increasing access to food supplies.
An additional problem is the prevalence of storms and changes in precipitation with current climate trends (e.g. more positive SAM), particularly in the West Antarctic peninsula. Increasing wind and storms modify/reduce the sea ice environment, and increase precipitation, which combined with increasing temperatures leads to fast snow accumulation followed by snow melt and nest flooding, which sometimes occurs during egg laying and incubation, leading to egg mortality.
What about the impact of krill fishing?
So far, there is limited evidence to suggest that commercial krill fishing is affecting penguin populations, but there is potential for this to occur where large catches are taken from within areas close to colonies where breeding penguins are foraging, Scientists at BAS are working with international bodies to ensure that krill fisheries are managed in a sustainable way that minimises any potential impact on Antarctica’s marine life. This includes limiting the total amount of krill that fisheries are allowed to capture and designing closed areas and seasons from which fishing activities are excluded.
How much do we know about penguins?
The penguin colonies studied by BAS near its Signy and Bird Island research stations are among the best-studied colonies in the world. The long-term research programme provides a valuable insight into how these engaging animals are responding to changes in their habitat.
Because penguins breed on land or ice, scientists have a good understanding of this part of their life-cycle. But because these seabirds can spend three-quarters of their lives in the ocean – more than any other bird – studying them is challenging. As a result, we are only now beginning to discover what penguins do when they are away from land.
How do scientists study penguins?
Scientists at BAS have developed innovative technology to study penguins on land and at sea. To monitor a colony of macaroni penguins at Bird Island Research Station the science team developed and installed a ‘penguin gateway’. As tagged birds pass between the colony and the sea, the ‘gateway’ records the tag number and the time and direction of travel. This allows scientists to deduce how long birds spend foraging at sea and how much prey it caught in that time, while reducing the need to handle the birds repeatedly during the study. A joint project with Japan’s National Institute of Polar Research obtained the first observations of penguins foraging underwater thanks to miniature digital cameras attached to the birds’ backs. BAS scientists are able to track penguins at sea using tiny GPS and geolocators devices, which weigh only a few grams and are attached to penguins’ back feathers or leg rings. All of these techniques help reveal the reasons for success or failure of penguin colonies and help build a better picture of the overall state of the Southern Ocean ecosystem.
Fact file
- There are 17 species of penguin. All live only in the southern hemisphere.
- There are around 20 million breeding pairs of penguins in the Antarctic.
- Although bigger species exist in the fossil record, the world’s largest penguin is the emperor, standing around 115cm tall and weighing in at 40kg.
- Because they breed on sea ice around Antarctica, emperor penguins may be the only species of bird never to set foot on land.
- Somewhat ungainly on land, penguins are superb divers and swimmers. Unlike other birds, whose bones are light and air-filled, penguins’ bones are solid and heavy which reduces their buoyancy and helps them to dive deep.
- Penguins’ closest relatives are petrels, albatrosses and divers.