Roosters may be able to recognise themselves in a mirror

A Maline rooster in front of a mirror

Sonja Hillemacher

Roosters act differently when faced with another chicken versus just their own reflection. This may mean that the birds can recognise themselves in a mirror, a key test of self-awareness in animals. The way researchers tailored this mirror test to roosters may open up new methods of determining self-recognition in a diversity of animal species.

In the traditional mirror self-recognition test, developed in 1970, researchers place a mark on an animal’s body in a spot that it could only see reflected in a mirror. They note if the animal inspects or touches the mark while examining its reflection, suggesting it understands the reflection represents its own body. Precious few non-human species have passed this test, but those that have include some great apes, dolphins, elephants and magpies. In recent years, a few researchers have claimed other species – such as penguins, horses, cleaner wrasse fish and manta rays – have passed the test, but not without controversy.

Results from this test are often highly variable. Sonja Hillemacher at the University of Bonn in Germany and her colleagues wondered if this has less to do with the animals not recognising themselves, and more to do with the fact that there is little natural motivation for many animals to investigate the marks. Looking at behaviours relevant to a species’ day-to-day life may give more reliable insights, she says.

So the team turned to roosters, which loudly alert other chickens to the presence of nearby predators, but generally stay quiet when alone. In the lab, the researchers tested 68 roosters one by one in an arena divided down the middle by a wire mesh. They placed a bird on one side, and either left the other side empty or put another rooster in it. Then they added a mirror to the divider for some tests. To mimic a threat, they projected the silhouette of a hawk on the ceiling above the arena.

The researchers found that when a rooster was paired with another rooster, it raised the alarm far more often than when it was alone in the arena, regardless of whether it could see its own reflection. Having another rooster present but blocked from view behind a mirror led to similarly few alarms, suggesting roosters distinguish between reflection and reality through vision, not smell or sound.

Since the birds acted similarly when alone and with a reflection, they may realise their reflection is of themselves, the researchers say. This would point to self-recognition possibly being more prevalent across the animal kingdom than previously thought, says Hillemacher.

“This is exciting, as it moves away from the rigid dogma that the mark test is the only valid test for self-recognition in animals,” says Nathan Emery at Queen Mary University of London.

Emery thinks the traditional mark test isn’t appropriate for testing self-recognition in non-apes, as most other animals don’t have hands available for easily investigating their own bodies. Notably, when Hillemacher and her colleagues put the roosters through the mark test, the birds failed.

“Ultimately, the animals are doing what they always do. We have to be the clever ones to find the right paradigms to reveal the skills they already possess,” says Emery, who was not involved with the research.

Both Emery and Hillemacher think it’s premature to say chickens definitely recognise themselves in their reflections. It’s possible the strange behaviour of a reflection – mimicking your every movement, for instance – is unsettling enough to perturb the natural alarm response.

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