Male bowerbirds create optical illusions with their bowers — grand exhibits made of sticks and decorated with stones and other objects to impress females — probably to boost their attractiveness.
The male great bowerbird (Chlamydera nuchalis) builds a twig-lined avenue, roughly 60 centimetres long and ending at a 'court'. The female looks down the avenue to the court, where the male squawks and hops to entice her. John Endler at Deakin University in Geelong, Australia, and his colleagues noticed that the objects lining the court floor were arranged by size — smallest at the front, largest at the back (pictured left) — creating an optical illusion known as forced perspective. The team says that the size gradient makes the male in the court look larger or more striking than he actually is.
When the researchers reversed the pattern (right), the male bowerbirds restored the size gradients within three days and had the optical illusion back to normal within two weeks.
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For a longer story on this research, see http://go.nature.com/jSTy1w
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Animal behaviour: Avian optical illusions. Nature 467, 255 (2010). https://doi.org/10.1038/467255a
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DOI: https://doi.org/10.1038/467255a
