In a bizarre incident, 64 endangered African penguins (Spheniscus demersus) have been killed in South Africa after being stung in and around their eyes by Cape honeybees (Apis mellifera capensis).

Rangers from the South African National Parks organization (SANParks) discovered 63 of the 64 dead penguins among a colony near Cape Town in Table Mountain National Park on Friday, Sept. 17. African penguins are a protected species in South Africa and are currently listed as endangered on the International Union for Conservation of Nature (IUCN) Red List, with around 42,000 mature individuals globally.

"The deaths occurred suddenly sometime between Thursday afternoon and Friday morning," SANParks said in a Facebook post. "No external physical injuries were observed on any of the birds."

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The dead birds were transported to the Southern African Foundation for the Conservation of Coastal Birds (SANCCOB) for necropsies (animal autopsies) to determine why so many penguins had suddenly died.

"After tests, we found bee stings around the penguins' eyes," David Roberts, a clinical veterinarian at SANCCOB, told French news agency AFP. "There were also dead bees on the scene."

The leading hypothesis is that a swarm of Cape honeybees attacked the penguin colony, although it is unclear why the bees attacked the penguins or why they stung them particularly around their eyes, SANParks said.

"This is a very rare occurrence," Roberts said. "We do not expect it to happen often, it's a fluke."

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Another dead penguin with stings around its eyes was discovered on Saturday morning (Sept. 18) at a nearby beach; that penguin likely died from the initial bee attack and not during a second attack, SANParks said.

"No more dead African penguins were found on site today, and we will continue to monitor the situation," Alison Kock, a marine biologist at SANParks, said in the statement on Saturday.

Originally published on Live Science.