How to count penguins

Tracking the size and whereabouts of bird populations is essential for protecting species under threat. For long-lived seabirds, like penguins, early detection of population changes helps guide conservation planning, prioritise actions, and assess management effectiveness.

The UK Overseas Territories are home to nine species of penguin: Northern Rockhopper, Southern Rockhopper, Macaroni, Magellanic, King, Gentoo, Adelie, Emperor,  and Chinstrap. After albatrosses, penguins are the second most threatened family of seabirds, with ten species being of global conservation concern.

I have been studying (and counting) penguins for over two decades and have seen 16 of the world’s 19 species in the wild. Yet, when people ask how many penguins there are in total or of a certain species, I still start to sweat. Despite what you might think about a bird that can’t fly, counting penguins is no easy task.

For starters, penguin colonies are often bustling hives of activity, with mates needing to be found, partners courted, nests built, and chicks raised, all within a tight seasonal window. However, once the eggs are laid, one partner returns to sea to forage for food, while the other takes the first shift incubating the eggs. This is when life in a penguin colony becomes surprisingly calm, with birds staying put for days, or even weeks, on end, making it the ideal window for population surveys.

Some penguins are wonderfully cooperative: they breed in predictable, accessible places, with tidy, well-defined colonies, and faithfully return year after year. Others are decidedly less helpful, nesting in burrows, hidden in thick vegetation, or, if that is not challenging enough, on far-flung islands rarely visited by humans.

Emperor and King Penguins are a different story altogether. These species do not even build nests but instead incubate a single egg on their feet while standing in large, ever-shifting clusters on the ice or shorelines. These mega-colonies are a spectacular sight to behold, but a field biologist’s nightmare to count. It may sound surprising, but new penguin colonies are still being discovered, sometimes thanks to novel technology such as satellite imagery or drones and sometimes thanks to sheer luck.

For over a decade, I have been studying the endangered Northern Rockhopper Penguin (Eudyptes moseleyi), or Pinnamins, as the locals endearingly call their penguins, on Tristan da Cunha.

Tucked away in the central South Atlantic, midway between South Africa and South America, the islands of Tristan da Cunha (Inaccessible, Nightingale,Tristan da Cunha and Gough) are part of the UK Overseas Territories, and home to over 90% of the global Northern Rockhopper Penguin population (the remaining 10% are found in the French Southern Territories on St Paul and Amsterdam Islands in the southern Indian Ocean).

Gough Island, 380 km south-southeast of the Tristan archipelago (Inaccessible, Nightingale and Tristan da Cunha), is a UNESCO World Heritage Site (together with Inaccessible Island) and the only breeding site for this penguin south of the Subtropical Front (where warmer subtropical waters meet colder subantarctic waters).

In the Tristan archipelago, the Northern Rockhoppers lay eggs in September with chicks fledging from the end of December. On Gough Island, breeding begins about three to four weeks later, with eggs laid in October and chicks fledging January to February.

So, with austral spring in the air and penguin breeding season in full swing, it's time to count the penguins. Led by the Tristan da Cunha Conservation Department, regular counts have been carried out since 2006 on Gough and since 2009 on the remaining islands. This long-term dataset is invaluable for estimating population size, detecting trends, and guiding sustainable management decisions.

Unfortunately penguins neither raise their flippers or flock out to greet us to be counted, so survey methods at each site needs to be chosen according to habitat, colony extent and topography.

On Tristan da Cunha and Gough, penguins breed along rocky shores. Here, the accessible terrain allows for direct counting of breeding pairs, by carefully walking along (or through) colonies. Personally, I swear by the trusty hand tally counter, a small clicker with a four-digit display. One click per penguin. Moving slowly through the colony brings you close to the birds: some curious, and some angry, about the intrusion. If you stand still long enough, they will wander over, and the boldest will tug on your trousers or peck your boots.

In contrast, on Nightingale, Alex and Inaccessible islands, penguins breed inside dense, 2m high (tussock) grass. From a penguin’s perspective, being nestled into the depths of the tussock provides wonderful protection not only against the elements but also against predatory birds such as skuas. But it does present a logistical challenge for fieldworkers. Ground counts are impossible, so breeding pair numbers are instead estimated from colony area and average nest density.

For colonies inaccessible from land or sea, such as Rockhopper Point on Gough, scan counts are done from a vantage point, with two observers independently tallying incubating birds using binoculars and clickers. Since 2014, the colony has been photographed annually from the same location, producing high-resolution images. Incubating birds are then counted using a bespoke software (iTag).

Given the species’ stronghold in these islands, any change in the Tristan da Cunha population would have a substantial impact on the global conservation status of Northern Rockhoppers. Monitoring population size and distribution here remains critical for safeguarding the future of this charismatic yet endangered species.

Although early results do not hint at substantial changes in breeding pair numbers, our methods have improved since the last count which makes comparisons difficult.

My work with penguins has taken me across several continents, but working on Project Pinnamin alongside the local Tristan community and learning from their wealth of island knowledge has been a special privilege. I have visited the islands nine times so far and hope to again, helping to protect not only this penguin species but also the islands’ unique biodiversity.

Science alone cannot save threatened species, but it provides a powerful tool for local communities to turn data into practical and (hopefully) long-lasting conservation successes.