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Penguins from space - satellite images of penguin poo reveal the location of emperor penguin colonies

In 1911, three explorers defied perilous weather conditions in the darkness of the Austral winter to retrieve an emperor penguin egg. Nearly a century later, scientists find novel ways of using modern technology to continue their research on a species that only breeds in the most inaccessible of locations.

Why are emperor penguin population numbers important?

Emperor penguins (Aptenodytes forsteri) breed in colonies on the sea ice that surrounds much of the coast of Antarctica. These colonies can range in size from a few hundred to many thousands of pairs, however, scientists have been unable to estimate the total number of emperor penguins in Antarctica. The colonies generally only exist in the most inaccessible of locations and access during the harshest weather conditions is extremely difficult. In addition, we don’t know where all the colonies are located.

Estimates of the total number of penguins range between 200,000 and 400,000 pairs, but changes in the sea ice on which they breed can affect their breeding success and the size of the colony. We therefore need a more accurate assessment of their numbers to help us monitor future penguin population changes, and in particular, their response to climate change.

Emperor penguins (Aptenodytes forsterion) on the sea ice at Drescher Inlet, Brunt Ice shelf, Antarctica
Emperor penguins

Emperor penguin breeding cycle.

The unique breeding cycle of the emperor penguin starts in the Antarctic Winter. For a large part of their lives, emperor penguins live at sea, but during March and April they travel up to 150km across the sea ice to their colony sites. In May, after laying a single egg, the female passes it over to the male who incubates it while she returns to the sea to feed.

By the time she returns in late July or August, the male penguins will have endured temperatures as low as −50°C and winds as high as 200km per hour in order to protect their egg. He carefully balances the egg on his feet where it is covered by a thick roll of skin and feathers. The males will have lost around 45% of their body weight by the time the female returns. She will then look after their newly hatched chick while the male penguin takes his turn to feed at sea, trekking up to 100km across the sea ice.

Emperor penguin breeding cycle
  • March – April: Emperor penguins travel inland up to 150km from the edge of the pack ice. The emperor penguins breed the furthest south of any penguin species.
  • May: Female penguins lay a single egg which they pass to the male, then return to the sea to feed.
  • June – August: Male penguins incubate the egg for nine weeks through the harsh winter conditions — temperatures reach as low as −50°C and winds are as high as 200km per hour. The egg can be up to 70°C warmer than the outside temperature — emperors have a special combination of adaptations to achieve this, including a dense double layer of feathers and a large fat reserve.
  • July – August: Female penguins return from feeding to look after the newly hatched chick. Male penguins return to the sea to feed. Afterwards, both adults rear the chick.
  • November – December: Chicks fledge and sea ice starts to break up.

The breeding cycle is timed so that the penguin chicks fledge in December, before the sea ice breaks up in the summer — their soft, downy feathers are replaced by new, waterproof feathers that allow them to swim and fish for food — and the colony will then begin to disperse in late December and January. The colony will disperse earlier if the sea ice breaks up sooner than expected; but if the sea ice breaks up too early, penguin chicks can become stranded on ice floes and separated from their parents. The younger chicks that have not yet fledged and still depend on their parents for food will starve.

Past emperor penguin populations.

Although emperor penguins were first seen over 120 years ago, it wasn’t until 1911 that a team from Scott’s Antarctic expedition succeeded in collecting an emperor penguin egg in the middle of the Austral winter. Knowledge of the number and distribution of emperor penguins has increased gradually over the last 100 years, but is still poor due to the isolated location of their breeding colonies.

Emperor penguin colony at Halley Research Station
Emperor penguin colony at Halley Research Station

The sheer number of penguins in some colonies makes an accurate count of the total population a near-impossible task — each colony may number tens of thousands. Manual counts must take place in late winter or early spring, but access during this time is difficult and so few colonies are monitored on an annual basis. As the colonies become more accessible in the summer, sea ice melt means that many colonies will already have scattered.

Smaller bands of penguins will gather in sheltered locations for their annual moult in January and February, but these are temporary moulting groups that should not be confused with breeding colonies.

Estimates of the total number of emperor penguins are based on an assumption that 34 colonies exist, a number obtained from both recent research and records that are decades old. It is inevitable that some of these records are out of date, or the recorded location of the colony may be inaccurate, so before a more accurate count can be made we need to confirm that those 34 colonies still exist. Between May and September, the sea ice on which emperor penguins breed surrounds the entire continent, making it difficult to narrow down the search and locate both new and existing colonies.

Viewing penguins from space.

Satellite image showing guano stains of an emperor penguin colony in Halley Bay, Antarctica
Satellite image showing guano stains of an emperor penguin colony in Halley Bay, Antarctica

Emperor penguins are the only penguin species that breed on sea ice; and while ice formed on land may be discoloured by impurities such as moraine, sea ice is formed only from sea water and contains no such impurities. The black and white colouring of the emperor penguins makes them blend into the shadows on white sea ice, so they can be practically invisible in low resolution satellite images. However, these satellite images can detect the guano (faeces) of large groups of penguins, which stains the sea ice light brown.

BAS mapping expert Peter Fretwell and penguin ecologist Dr Phil Trathan surveyed between 85-95% of the sea ice surrounding the Antarctic coast for evidence of guano stains. They used satellite image scenes from the Landsat Image Mosaic of Antarctica (LIMA), a seamless, cloud free mosaic of satellite images of Antarctica acquired between 1999 and 2004. As the breeding colonies disperse in January and February, it was important that the images were from the right time of year. Where the LIMA images were at the wrong time of year, they used satellite images taken from other sources.

The satellite pictures revealed 38 colonies, 4 more than were thought to exist. Of the 38 colonies found: 

  • Ten are new;
  • Six that were previously thought to exist were not found or have disappeared; and
  • Six have been re-positioned by over 10km.

To verify these findings, staff at the UK Halley Research Station identified one colony, and a tourist operator working in the region was able to confirm the existence of another. This confirmed to Fretwell and Trathan that the method they developed was valid. However, they noted that the satellite pictures could not pick up smaller colonies of fewer than 500 pairs of emperor penguins.

Fretwell and Trathan also noted that although Adélie penguins are known to haul out on to sea ice, their breeding colonies are located on rock, and so cannot be picked up using the LIMA satellite pictures. This means that the emperor penguin colonies cannot be confused with those of Adélie penguins.

Further investigation.

Further reading

Penguins from space: Faecal stains reveal the location of emperor penguin colonies by Peter T. Fretwell and Philip N. Trathan is published in the June 2009 issue of the journal Global Ecology and Biogeography.

The guano stains found in the satellite pictures point to the locations where the colonies exist, however the size of the stain cannot be used to measure the colony size. The pictures used are taken at different times of the year — in winter the colony will huddle together for warmth, but in spring after the chicks have hatched, they will begin to spread out and the stains seen in the satellite images will become larger.

Finding the colonies is just the first step towards an accurate count of emperor penguins. Next, scientists will use other techniques, including high resolution satellite data, to count the number of penguins in each of the 38 colonies. The data gathered will be used to monitor and predict future population changes, and assess how vulnerable the colonies are to the effects of environmental changes.

Photo
Map showing the location of emperor penguin colonies found in this study.