African Penguin Refugees: Tenfold Decrease in Optimal Nesting Habitat Recorded Over the Past 22,000 Years

At least 15 sizable islands, the largest of which is 300 square kilometers in size, would be visible in the distance from the western coast of southern Africa during the Last Glacial Maximum (LGM), more than 20,000 years ago, and they would be buzzing with hundreds of millions of marine birds and penguin colonies.

Climate refugees from a distant past?

(Photo : ULISES RUIZ/AFP via Getty Images)

Imagine that between 15,000 and 7,000 years ago, sea levels rose by up to 100 meters, gradually engulfing these vast islands, leaving only little hilltops and outcrops above the water, as per Phys.org.

This has caused a tenfold reduction in acceptable nesting habitat for African penguins over the previous 22,000 years, leading to a sharp decline in the species' population.

The evolutionary genomics research group in the Department of Botany and Zoology and the School for Climate Studies at Stellenbosch University (SU) developed this pale historical map showing the geographic range of African penguins.

They want to shed new light on the current vulnerability of the last remaining penguin species in Africa with this research.

According to Dr. Heath Beckett, the primary author of the paper and a postdoctoral scholar at SU's School for Climate Studies, this paleohistorical vision of numerous millions contrasts sharply with the actual reality of an African penguin population collapse that occurred after 1900.

A three square kilometer island off the West Coast known as Dassen Island was home to an estimated 1.45 million penguins in 1910.

But by 2011, only 21,000 breeding pairs of African penguins remained in South Africa, and by 2019, that number had further decreased to just 13,600.

Only seven breeding colonies in South Africa currently house 97% of the country's penguins.

Estimates Of The Magnitude Of The Penguin Population From Antiquity

So how did southern Africa's southern and western coastlines seem during the previous Ice Age? And what does it reveal about the size of the penguin population?

The researchers analyzed topographic maps of the ocean floor off the coast of southern Africa to locate potential historical islands lying at 10 to 130 meters below present sea levels because penguins prefer to breed on islands to avoid predators on the mainland.

Islands have to provide shelter from land-based predators and have appropriate foraging grounds for sardine and anchovies within a 20-kilometer radius in order to be considered suitable for penguins.

The researchers discovered 15 sizable islands off the West Coast, the largest of which was a 300 km2 island that was 130 meters below the sea's surface, indicating that sea levels were significantly lower during the last Ice Age.

Then, taking into account the recent 15,000-7,000-year rise in sea levels, scientists discovered 220 islands that might have offered favorable nesting conditions for penguins.

216 of the islands have a surface area of less than one square kilometer, with some being little bigger than 30 m2, or about the size of a pebble.

Presently, Seal Island and Penguin Island, both less than 1 km2, Robben Island (about 5 km2), Dassen Island (about 3 km2), Possession Island (about 1.8 km2), and Possession Island are the five largest islands off the West Coast of Southern Africa.

The researchers then computed penguin population estimates based on available island area using the earliest population density estimations, considering that penguins typically nest at most 500 meters from the shore.

They calculate that 6.4 million to 18.8 million people could have lived in the southern Cape seas during the Last Glacial Maximum using this method.

But between 15,000 and 7,000 years ago, as sea levels rose, the habitat used by African penguins to nest drastically shrank.

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Implications For Managing Conservation

Although this discovery poses serious issues, the researchers contend that it also reveals the possibility of an African penguin reserve of resilience that may be used to support its management and conservation in the face of a bleak future, as per ScienceDaily.

According to Dr. Beckett, when island habitat shrunk significantly, changing sea levels would have required several relocations of breeding colonies of African penguins across time periods of millennia, if not even shorter time scales, as well as fierce competition for breeding space.

Given the historical adaptability of response, conservation managers have some latitude to offer acceptable breeding space, even in mainland areas, as long as proper nesting places are provided.

Prof. Guy Midgley, co-author and acting director of the School for Climate Studies at Syracuse University, claimed that this millennial-scale set of selection forces would have favored the species' great colonizing capabilities.

Given the slightest chance, they will survive completely.

He highlighted that they know how to do this and that island hopping has before rescued it.

But even if relocation is an option, how much longer will it take to survive given the increasing constraints of modern society?

Penguins and other marine creatures may not have a chance when vying for the same food source with the commercial fishing sector and humanity in general.

Related article: Three Endangered African Penguin at Arizona Aquarium Give Hope for Conservation Efforts Against Species Population Decline