In conversation with… penguin counter Peter Fretwell

07/08/2025

We catch up with British Antarctic Survey cartographer Peter Fretwell to talk about penguins, penguins, and, err, more penguins.

Dr Peter Fretwell is an award-winning cartographer and leading scientist at the British Antarctic Survey. He pioneered the use of satellite imagery to find and monitor polar wildlife, a project that has led to him discovering almost half of the world's emperor penguin colonies. He is a fellow of the Royal Geographical Society and has completed six field seasons in Antarctica. 

His second book, The Penguin Book of Penguins, follows the 2020 coffee table book Antarctic Atlas, and features illustrations by his wife, Lisa. We caught up with Peter to chat, unsurprisingly, about penguins.   

You’ve worked for the British Antarctic Survey for over 20 years. Is it fair to say you count penguins?

Amongst many other things! For the last seventeen years, I have been using satellite imagery to find, count and study penguins, but I also use satellite imagery to study many other polar animals and use remote sensing more generally in polar regions to look at ice, vegetation and various other environmental conditions.

Peter has worked at BAS since 2002 (Peter Fretwell)

In terms of monitoring penguins from space, please tell us about the process.

If we are looking at emperors, first we have to find them. Surprisingly, many of the colonies move around, so we use freely available imagery like Landsat or Sentinel2 to detect them by looking for those tell-tale stains on the ice. The advantage of these satellites is that they are free to use and are continually taking imagery, but the resolution is too coarse to count or estimate the populations from.

A satellite image of an emperor penguin colony (MAXAR/BAS)

When we have found them, we task the very high-resolution Earth observation satellites to take an image of each colony. These are powerful enough so that we can see individual penguins, but often the emperors huddle together, so we have to estimate the numbers based on their area. We do this using automated machine learning algorithms that isolate penguins from the rest of the image. 

When we know the area of penguins at each colony, we can multiply it by a density estimate, which gives us the number of penguins. We’ve been doing this every year for emperors of over fifteen years now, and have also used similar technology for several other penguin species.

Please tell us about The Penguin Book of Penguins.

It's been a book that has been a joy to write. Penguins are such amazing creatures, with incredible adaptations and abilities. After working on them for so long, I have been able to weave in many anecdotes, tales and personal observations, which hopefully convey some of my love for these charismatic animals. 

Peter's book is due out in September and can be pre-ordered via UKAHT (Penguin Random House)

But what I have also tried to communicate is the checkered history of interaction penguins with had with humans ever since we discovered them and a serious message about the threats that many of the species are now facing with climate change, habitat loss, pollution and industrial fishing. The book is written so that it is accessible to everyone, and my wife has illustrated it with lots of lovely pencil and pen and ink illustrations.

We usually leave this question until last, but what’s your favourite species of penguin?

I am always going to go with emperors. As I say in my book, as scientists we are not really supposed to have favourites, but as many of the highlights of my science career have been with emperors, I have to plump for them. There is also something magical about visiting an emperor colony. So few people get to see those fluffy little chicks and hear the evocative soundscape of their breeding grounds; it is a truly incredible experience.

Emperor penguins (Credit: Vladsilver/Shutterstock)

Where do you stand on the northern/southern rockhopper debate? Two separate species?

Yes. They are clearly morphologically different, and only history has clumped them together. What is trickier is that other species should also be separate. This is also something that I discuss in the book: how many species of gentoo are there, should the white flippered penguin be a separate species, and should there be three, rather than two species of rockhopper. And if you did that, where would you stop? Moreover, should we base taxonomy on genetic or morphological or behavioural differences?  There is no truly correct answer, and it is something that we are going to be debating and arguing about for years to come.

A Southern Rockhopper penguin (Credit: Giedriius/Shutterstock)

And do you have a favourite story about penguins?

There are many. One particular example is the story of penguins turning up at Halley Station. Every year, a few penguins, mostly emperors, but sometimes Adélies, turned up at our  Halley Station, 20km inland from the coast of Antarctica. For many years, the BAS resupply route went close to the emperor colony, and we would lay a line of empty fuel drums from the coast to the station to mark the way for the tractors and snowcats. 

It seemed that penguins, being curious but short-sighted, saw the drums in the distance and mistook them for other penguins. One or two would waddle over to them, only to realise when they got closer that the drums were not penguins, but then they would see another drum and do the same thing. After 20km of repeating the same mistake, they would arrive at the research station rather confused, and we would have to put them in a box and tow them back to the colony in a skidoo.

What is one thing you hope readers will take away from the book?

How incredibly special and unique penguins are, but also how their future is at risk through human activity. Many of the species are under threat, often inadvertently, and it will take effort and engagement to change the population trajectories of those species most affected. 

Peter gets up close to emperors in Antarctica (Peter Fretwell)

Do you still have a dream destination you haven't visited?

There are many. I have discovered many emperor penguin colonies, so going to one of the ones I have discovered would be high on my list of places I would like to visit.

What's next for you?

I have a number of new science projects, mostly on penguins, but there are other polar species that I am working on, too. We are seeing rapid change in the Antarctic, especially the Peninsula and West Antarctica, and it is affecting the ecosystems there. It is something that is happening before our eyes, but many of the areas of the continent are so remote that we don’t understand or even consider what might be happening to the animals there as the temperature and ice conditions change. I think that much of my future work will be using satellite imagery, which is getting more and more powerful, to document and understand these changes.

What luxury item would you take if you were working at Port Lockroy for the season?

Having spent many weeks in tents in Antarctica, I know how important food is when you are isolated. So I would take a pack of tasty treats like Peperami, olives, croutons, and a few other things from the deli that can spice up a meal.

The Penguin Book of Penguins is a joyful and informative book that introduces us to the main species of penguins and the fascinating lives they lead, including their history, evolution, behaviours, and habitats. It is released in September and is available for pre-order now from UKAHT.