African penguins recognise their partners by the spots on their chest

African penguins may identify their partners by the patterns of spots the birds sport on their chests. This is the first time researchers have pinned down a feature that any bird uses for visual recognition.

The dots on African penguins (Spheniscus demersus) appear when they are 3 to 5 months old. The birds moult every year, and the dots reappear in the same position when the new plumage emerges, says Luigi Baciadonna, who was at the University of Turin, Italy, during this project.

In 2021, Baciadonna and his colleagues found that these penguins tune in to both the vocal calls and visual features of their colony mates. But it wasn’t clear if looks alone were enough.

Now, the researchers have tested 12 birds at a zoo near Rome by tracking the animals’ responses to life-size images of other African penguins.

Individuals of this species form lifelong pair bonds, and they were found to spend more time gazing at a picture of their partner than they did a picture of a different familiar penguin. This was true even when the heads on the penguin pictures were obscured.

When the test subjects encountered two images of their partner, one of which had the spots artificially removed, they preferred the dappled image. But the preference for their partner disappeared when the birds were presented with unspeckled versions of both their mate and a different bird. Together, the results suggest that the animals clue into these spots.

The ability to discriminate a mate visually could be vital when penguins are trying to find their nest in a large, loud and crowded colony, says Baciadonna. It isn’t clear whether other penguins, particularly those that roam instead of nest, possess this skill.

“Given how goofy penguins can seem – almost stumbling over their feet as they walk, for example – the birds may not seem like they are all that bright, says Baciadonna. “But we showed in these two or three experiments that actually they are quite complicated and complex,” he says. “They’re also clever.”

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