Great bowerbirds of northern Australia

Male bowerbirds may look like they’re at the mercy of picky females, but these males have an optical illusion up their sleeves
Contributor

Bec Crew

Contributor

Bec Crew

Becky Crew is a Sydney-based science communicator with a love for weird and wonderful animals. From strange behaviours and special adaptations to newly discovered species and the researchers who find them, her topics celebrate how alien yet relatable so many of the creatures that live amongst us can be.

ByBec Crew March 19, 2015 Reading Time: 2 Minutes

MEET THE LOVELY great bowerbird (Chlamydera nuchalis) and the wonderful magenta crest that adorns the back of his head and the nape of his neck. Found in northern Australia from Broome over in WA, to Cape York Peninsula and down as far as Mount Isa, this small bird keeps to the dense bushlands, forests, and mangrove swamps that can sustain its elaborate courtship routines.

The males, which grow to about 35cm long, have to construct a twin-walled tunnel bower, stretching 1m long and 45cm high, within a cleared ‘courtyard’ just to catch the glance of a female. And even if he builds and maintains the tallest, most robust bower in the region, he’s still not going to get much of a glance if he’s not decorating it at either end with hundreds of colourful paraphernalia – rocks, seeds, bones, shells, pieces of glass, and all kinds of plastic objects of all kinds of colours.

The idea is for the female to enter the bower tunnel to inspect the male’s handiwork, while also inspecting his own pink crest, which he’ll show off to her in the most enthusiastic fashion.

Are female bowerbirds really in control?

Interestingly, while it looks like the female holds all the power in this scenario – if she and every other female like her walks, the bower and its adornments were all for naught – but by stepping into that bower, she’s unwittingly allowing her point of view to be controlled and manipulated for the benefit of her would-be suitor.

It’s an optical illusion called ‘forced perspective’, and as Ed Yong notes at Discover Magazine, we’re subjected to it every time we walk into Disneyland. As we’re funneled through the entrance, we see the castle looming in the distance, but what we see isn’t actually what’s there.

“The castle’s upper bricks and the upper levels of Main Street’s buildings are much smaller than their ground-level counterparts, making everything seem taller,” says Yong. “The buildings are also angled towards the castle, which makes Main Street seem longer, building the anticipation of guests.”

In much the same way, the male bowerbirds create an optical illusion for the females by placing the smallest objects in front of the bower, and the largest ones near the back of courtyard. From inside the bower, the female sees the near and far objects as being the same size, and the illusion makes the courtyard seem more compact than it actually is, says Yong, which is the opposite of what Disneyland is trying to do to us. Perhaps bigger isn’t always better in the eyes of a female great bowerbird?

Bowerbirds bowers particular about their creations

In 2012, a study by researchers at Deakin University in Victoria found that the patterns the males place their objects in around the bower are entirely unique. Even when the researchers went in and changed the patterns to make the illusions stronger, the male bowerbirds changed them back to the way they were.

“The birds put the gradients back to their previous, inferior values within a few days,” one of the team, John Endler, told Australian Geographic at the time. “It’s a puzzling but very interesting result.”

I guess the males don’t want word to get out that a human decorated their bowers for them. There’s no living that down, I don’t care how pink your neck crest is.