Counting penguins from space

Scientists have a new tool in their kit for counting populations of penguins in Antarctica. An international team has published a paper about using very high-resolution satellite imagery for the job. Their study has revealed that there are twice as many emperor penguins (Aptenodytes fosteri) in Antarctica than was previously thought.

Pan-sharpening technique

When looking down at things on Earth from space, even with the best satellite images, it can be hard to tell the difference between a penguin, a dark ice shadow or even a pile of penguin poo. To get around the problem, the scientists used a technique called pan-sharpening to further increase the resolution of the satellite imagery – and where they were able to, they calibrated the analysis using ground counts and aerial photography.

Estimating penguin numbers has always been tricky. They often breed in remote and inaccessible areas with temperatures as low as -50 °C. They also like to huddle together to stay warm.

Estimates of emperor penguin numbers doubled

However, in this first comprehensive census taken from space, scientists were able to count over half a million emperor penguins. “We are delighted to be able to locate and identify such a large number of emperor penguins. We counted 595,000 birds, which is almost double the previous estimates of 270,000–350,000 birds,” says lead author and geographer Peter Fretwell at British Antarctic Survey (BAS).

This team analysed 46 emperor penguin colonies around the coast of Antarctica – seven of these colonies were either completely unknown (four) or had been suspected but not confirmed (three).

Efficient research with little environmental impact

Co-author of the research Dr Michelle LaRue from the University of Minnesota Polar Geospatial Centre says using remote sensing (satellite imagery) is an enormous step forward in Antarctic ecology,

because we can conduct research safely and efficiently with little environmental impact and determine estimates of an entire penguin population

Dr Michelle LaRue

The method is also cost effective and can be applied to other poorly understood Antarctic species to strengthen on-going field research and to provide accurate information for international conservation efforts.

In their paper, published in the 13 April 2012 issue of PLoS ONE, the researchers write that getting an accurate tally of emperor penguin numbers now is crucial as it provides a baseline with which to measure any impact of climate change on the population. “…recent research indicates that numbers may decrease significantly in coming decades. These studies have highlighted the susceptibility of emperor penguins to changes in sea ice distribution. Recent recorded changes in sea ice are substantial and predictions suggest sea ice variation will increase with predicted climate change. The subsequent change in marine food webs and other possible developments linked to climate change such as increased predation, increased competition and an increasing frequency of storm events is likely to impact on their breeding success and colony viability…”

Comparison with ground counts

In a 2012 press release from the Australian Antarctic Division (AAD), the Division reports that AAD biologist Dr Barbara Wienecke undertook ground counts of penguin colonies at three sites in east Antarctica to compare them with the numbers derived from the satellite imagery.

Dr Wienecke reports that, despite the unexpectedly large number of penguins counted, she notes that some of the known colonies have been impacted on in recent years.

“The populations of two large colonies have already significantly decreased in size, and one small one has all but disappeared and others are beginning to show signs of change. We think that earlier spring warming is leading to loss of sea ice habitat for emperor penguins, making the northerly colonies more vulnerable to further climate change.”

The research is a collaboration between British Antarctic Survey, University of Minnesota/National Science Foundation, Scripps Institution of Oceanography and the Australian Antarctic Division.