Why are ravens suddenly attacking the world’s smallest penguins?

ByKenna Hughes-Castleberry

Published January 29, 2024

Across the shallow beaches of Australia’s Phillip Island, shrieks like broken whistles fill the air. Tiny penguins, just a foot tall and weighing three pounds, fight for their chicks’ lives from their burrows. Their attackers: the island’s ravens.

The ravens will spend several days observing the burrow of a little penguin—also known as a fairy penguin—before attacking. They work in pairs, with the larger one distracting the parent penguin while the smaller one digs a hole into the burrow from above to snatch the eggs or chicks. In one particularly violent attack, researchers saw a pair of ravens throw a parent penguin off a cliff before raiding the burrow. But usually, says BirdLife Australia’s Kasun Ekanayake, the ravens harass the parent penguin for several hours until it abandons hope and gives up.

This hasn’t always been the case. In fact, it was only about 20 years ago that researchers noticed the ravens, which arrived from mainland Australia in the 1970s, were starting to prey on the island’s penguins—about their equal in size. Now, as each species develops new strategies to try to outsmart the other, researchers are racing to find ways to stop the raven attacks before they begin to affect the penguin population.

Little penguins, which are found across the southern coast of Australia and New Zealand, are not endangered, but at more than 40,000 breeding birds, the Phillip Island colony is the largest of all. Island ecosystems exist in a state of delicate equilibrium, and it takes only one small change for that harmony to collapse.

“As far as we know, it seems like other penguin colonies do not suffer from such raven attacks,” says Mike Weston, a professor of wildlife and conservation biology at Melbourne’s Deakin University who has been studying the phenomenon. “That suggests we have a local raven population who has learned to do this, and the risk of this behavior spreading is real.”

Understudied and underappreciated predators

Invasive foxes used to be the greatest menace to the Phillip Island penguin colony, with over 3,000 penguins falling victim, but a concerted eradication effort finally left the island fox-free in 2015. (See the little penguins’ “Penguin Parade” on Phillip Island, which helps fund research and conservation efforts.)

Ravens, on the other hand, pose a much more complex challenge.

The corvids “have been greatly underappreciated as a predator of wildlife,” Weston says. Their ability to thrive in urban areas, eat a range of different animals and plants, and their incredible intelligence makes the threat they pose especially hard to mitigate. These characteristics also explain why their numbers are on the rise. Complicating matters further: No one is quite sure why the ravens began preying on little penguins in the first place—or how it spread.

A 2021 study established that the predatory behavior comes from social learning rather than genetics, but a lot is still unknown. “There was likely some kind of innovation, which spread through the population. Ravens are very intelligent, and some corvids are known to learn just by watching other ravens solve puzzles,” says Weston, the study’s coauthor.

In 2013, researchers found that more than 60 percent of the penguin clutches they were monitoring had been attacked or destroyed. Just two years later, only 30 percent of observed clutches had been attacked, suggesting the penguins had adapted to the raven attacks to make their burrows safer. So far, the island’s penguin population has stayed stable since 2015.

That’s because the rate at which ravens attack penguin burrows fluctuates from year to year, according to research by BirdLife Australia’s Laura Tan, depending in part on the availability of alternative sources of food.

The ‘unkindness’ of ravens

Weston, Tan, and colleagues also experimented to see if penguin DNA could be detected in raven feces, which could give researchers better insight into how widespread penguin predation is among the island’s ravens. While the technique didn’t prove as helpful as the researchers had hoped, it did show that the ravens eat many more bird and mammal species than previously realized.

That means the growing number of ravens is not just a concern for little penguins, Tan says, but for other vulnerable species as well—especially other ground-nesting birds.

“What surprised me is the sheer breath of the raven diet,” Weston says. “Their versatility is amazing.”

The ravens have also been known to blind livestock with their sharp beaks or stab other shorebirds to death before eating the bodies. These behaviors lend credence to their collective characterization: A group of ravens is called an “unkindness.”

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