Nature's greatest architects
The lengths to which Australia’s male Great Bowerbirds will go to attract females are again receiving international interest.
The bowerbird research of Alfred Deakin Professor John Endler has recently appeared on the US-based Science website "Science Friday" and is soon to be filmed by two separate BBC film crews – one doing a series on urban birds and the other on bird senses.
The male Great Bowerbird spends hundreds of hours preparing a bower that will be used solely for mating, with the female going off to make her own nest and raise the chicks herself. The bird is found in Northern Australia, from Broome - across the top end - to Charters Towers and Townsville in Queensland.
Professor Endler, from Deakin’s Centre for Integrative Ecology, has uncovered an extraordinary use of perspective by the male, which lays the stones, shells and bones that line the entrance to the bower according to size so that when the female is within the bower she has the illusion - called "forced perspective" - that the paving is all the same size.
Professor Endler and his students have shown that the better the illusion - and the more even the patterns appear - the greater the mating success. The flooring, generally grey and white, is punctuated with coloured objects, often red, that could even include coke bottle lids or cigarette lighters.
One explanation as to why the males undertake this painstaking task is that the visual illusions and coloured objects attract the female’s attention and keep her in the bower longer, thus increasing the chances of mating.
The discovery makes bowerbirds the only known animal – apart from humans – that is able to create a scene with altered visual perspective, and one constructed for viewing at a particular angle – from within the bower. When initially publicised in 2010, the finding received world-wide coverage, making “Discover” magazine’s list of Top 100 stories for 2010.
Professor Endler explained that the bower “is a poor place to lay eggs and raise young since there are plenty of predators on the ground.”
"All members of the Bowerbird and related families, such as Corvids (Crows, Ravens, etc) actually nest high in trees,” he said.
"The oddest thing, however, is the fact that, although Great Bowerbird bowers (built only by males) are beautifully finely thatched structures, the nests (built only by females) are sloppy piles of sticks, just like the nests of crows, ravens, currawongs or magpies.
"It's probably due to both predation avoidance and evolutionary constraint that the female doesn’t use the male’s bower. If it was built in a tree, then the walking and strutting and object arrangement would be very difficult, if not impossible. Where would they put all the coloured objects?"