Male bowerbirds entice females with optical tricks

LONDON - One of nature’s greatest artists was bending perspective long before Michelangelo applied the same technique to his Statue of David.

Male bowerbirds are well known for making elaborate constructions of sticks and decorative objects to attract a mate.

Michelangelo knowingly sculpted his master work, the Statue of David, with an over-sized head, over-long arms and large hands, reports the Daily Mail.

But he knew the statue was intended to be seen from below at a distance, adorning the facade of the Duomo in Florence. Viewed from this perspective, the proportions would seem correct.

Similarly, the male great bower bird modifies perspective by lining his “bower” with objects whose size increases with distance from the viewer - in this case the mate he hopes to attract, according to the journal Current Biology.

The effect is to make the elements of the construction seem more regular, which the researchers believe might be pleasing to the female.

Another advantage may be that the interior of the bower is made to look smaller than it really is. This in turn would make the male, standing in the centre of his “stage”, appear larger.

“Great bowerbirds are the first known animals besides humans who create a scene with altered visual perspective for viewing by other individuals,” said John Endler, from the Deakin University in Geelong, Australia, who led the research.

As in the case of the Statue of David, the effect only works from one viewing angle. Male great bowerbirds ensure that females see their bowers from a particular spot by constructing an “avenue” - two rows of tightly packed sticks with a stick floor - that opens onto a “court.”

Experimental manipulation of the courts showed how important the bird considers its geometrical meddling.

“When we reversed the gradient - putting smaller objects further away and larger objects closer to the avenue - the birds put the gradient back in three days,” said Endler.