Bowerbirds use visual trickery to lure lovers
Deakin University’s Professor John Endler has played a prominent role in a new study that claims male bowerbirds deliberately decorate their bowers to make themselves look larger to females.
The discovery makes bowerbirds the only animal - in addition to humans - known to create a scene with altered visual perspective, and one constructed for viewing at a particular angle.
Professor John Endler, an evolutional ecologist who is a recent prized research recruit to Deakin’s Centre of Integrative Ecology on the Geelong Campus at Waurn Ponds, says he noticed a consistent geometric size pattern while studying a species called the great bowerbird (Chlamydera nuchalis).
"It appears the males create a staged scene, only visible from the point of view of their female audience," says Endler.
"He places white and grey pebbles, bones, and shells in the court ... putting smaller objects near the front and larger ones further back.
"If you move stuff around, he'll move it back, not to the same spot as some reports claim, but certainly to the same distance from the front of the court."
Bowerbird males have long been known to make elaborate constructions full of objects to impress and attract mates.
The bowers have an avenue approximately 60 centimetres long that leads to a decorated court.
The female stands in the avenue watching the male displaying in his court.
Professor Endler says this staged scene only works from one viewing angle, which happens to be the avenue.
The forced perspective, particularly if birds see things the same as humans do, could lead females to "perceive the court as smaller than it is and therefore perhaps perceive the male as larger than he is”.
"It could make him look like a better catch or it might just make him easier to see against the background,” Professor Endler said.
Earlier research reports that colour is important to bowerbirds, white and grey objects as well as stronger colour like red and green.
"Interestingly they really seem to dislike yellow,” he said.
“That could be because they have a yellowish tinge on their chests, so they're looking for a contrast to make them stand out.
"Satin and regent bowerbirds like blue and yellow, which is why you see things like blue clothes pegs in their bowers. In the days before blue plastic they decorated their bowers with blue feathers and fruits like blue quandong."
Endler says it's too early to say whether the male feels for the female perspective.
"He spends 70% of time arranging the bower, so it could just be a case of decorating the bower to suit his own tastes rather than doing it to impress the females."
The researchers are now conducting further tests to see if these visual tricks to enhance the impression of size are related to success with mating.