Dozens of critically endangered South African penguins have been killed after a swarm of bees attacked a beach outside Cape Town.

Locals found 63 dead African penguins on Sunday in the town of Simon, near Cape Town, which is a nature reserve for rare penguins.

“After the tests, we found bee stings around the eyes of the penguins,” veterinarian David Roberts told AFP.

He continued, “There were also dead bees in the place. This is a rare occurrence and we do not expect much. It is just a coincidence.”

“Penguins should not die in this way. They are already in danger of extinction. They are a protected species,” the doctor added.

An autopsy showed that all of the penguins suffered from bee stings, in separate parts of their bodies.

The South African National Parks Department said samples from birds were also sent to be tested for diseases and toxins, explaining in a statement that “no external physical injuries were found in any of the penguins.”

African penguins, which live on the coast and islands of South Africa, are on the International Union for Conservation of Nature’s Red List, which means they are at high risk of extinction.