Penguins died en masse from a simple and painful cause: lack of food.
In two important colonies off the coast of South Africa, the vast majority of breeding birds likely starved to death over an eight-year period because their food sources collapsed, according to a study published Thursday.
The findings by a team of researchers from the South African government, the University of Exeter and other universities add to a growing body of evidence about a central threat to the survival of African penguins, which have seen their numbers decline and are now considered “critically endangered.”
Scientists focused on Dassen and Robben Islands, where the small bird, with its bray-like calls and distinctive black-and-white tuxedo markings, was decimated from 2004 to 2011, when the sardine stock it relies on declined sharply — leading to an estimated loss of 62,000 birds during that period.
Efforts to restore and maintain a reliable food supply for birds in foraging areas “appear to be essential for their long-term survival,” Richard Shirley, co-author and conservation biologist at the University of Exeter, said in a statement.
Today there are fewer than 10,000 pairs of African penguins, down from an estimated 141,000 pairs in 1956 and perhaps millions in the late 19th century. These birds, which are only about 2 feet long, are the only penguin species native to South Africa and mainly inhabit small islands off the coast of that country and neighboring Namibia.
Several factors have led to their sharp decline, including the harvest of guano, which penguins have historically used to develop suitable nests. But few risks are as great as shortages in sardines and the anchovies they feed on – supplies facing the impacts of climate change and commercial fishing.
Every year, African penguins undergo a molting process, which involves losing and replacing worn-out feathers to maintain warmth and waterproof. But during the several weeks this process takes, the birds must remain on the ground and unable to hunt.
Normally, they would have a feast to prepare for such a difficult period.
“They have evolved to accumulate fat and then rapidly as the body metabolizes these stores,” Shirley said. “They then need to be able to quickly restore body condition afterwards… So, if it is very difficult to find food before or right after molting, they will not have enough reserves to survive the fast.”
The researchers found that this is the situation that most likely led to the mass die-offs documented in the years after 2004, when the birds’ main food source fell consistently to less than a quarter of peak levels.
The study’s authors compared an index of food availability in the area over time with the proportion of breeding penguins that did not return to their colonies to molt. A clear picture emerged.
“Adult survival, especially during the crucial annual molt period, was strongly linked to prey availability,” Shirley said.
The sites the researchers studied represent “two of the most important breeding colonies historically,” according to co-author Azwiani Makhado of the South African Department of Forestry, Fisheries and Environment.
But the researchers added that the losses are not limited to these islands. “These declines are mirrored elsewhere,” Shirley said, noting that the species has suffered a roughly 80% population decline over the past three decades.
Thursday’s paper comes on the heels of another study conducted last month, which found that during years of fish shortages, African penguins tend to congregate in the same areas as commercial fishing boats, creating intense competition for a dwindling supply of prey.
These findings, published in the Journal of Applied Ecology, also used tracking information from Dassen and Robben Islands to document this “overlap density.”
In 2016, a year when sardine and anchovy stocks declined, about 20% of penguins were feeding in the same areas as active fishing vessels, according to the scientists’ analysis. In years when fish stocks were stronger, this number dropped to about 4%.
Increasingly in-depth research into food availability for African penguins is helping to shape management and conservation efforts around an issue that has been a focus for decades.
In recent years, the South African government has imposed “temporary” fishing restrictions, declaring some areas around major penguin colonies closed to commercial fishing for anchovies and sardines.
This year, an agreement between conservation groups and the fishing industry led to the South African High Court banning commercial fishing over the next decade near six important sites of African penguin breeding colonies.
The exclusion zones, designed to prevent the presence of vessels using “seine nets” to create a wall of nets surrounding the fish, include spawning areas on Dassen Island, Robben Island, Stony Point, Dyer Island, St. Croix Island and Bird Island.
The authors of Thursday’s paper said they hope the new restrictions will help slow the loss of African penguins. “However,” they write, “given the continuing impact of climate change on the abundance and distribution of their key prey, other interventions are likely to be necessary.”
In its most recent assessment of the species last year, the International Union for Conservation of Nature found that African penguins are “experiencing a very rapid decline in their numbers” and that the current population is “showing an alarming acceleration in the rate of decline.”
“This trend currently shows no signs of abating, and immediate action is needed to conserve the environment,” the organization wrote.
Shirley, the University of Exeter researcher, hopes the latest findings on prey availability will help highlight the urgent need to protect penguins — in part, he told Mongabay last year, because their loss offers a glimpse of a much broader potential loss.
“Despite being well-known and well-studied, these penguins still face the threat of extinction, which shows how serious the damage to our ecosystems is,” Shirley said.
“If an iconic species like the African penguin is struggling to survive, it raises the question of how many other species are disappearing without us noticing,” he said.