Are you having a difficult time finding the right girl for you? Have you ever been excessively concerned that she will not approve of how you organize all of your belongings? Well, maybe it is time you took a page out of the courting-book of a pro!
Greater Bowerbird. Image by Laura Kelley.
Bowerbirds belong to the genus Ptilonorhynchidae, which consists of 8 genera and 20 species found in different parts of Indonesia, Papua New Guinea and Australia. What sets these birds apart are the elaborate courtship displays of the male. Just check out this video of the Vogelkop Bowerbird from the BBC nature documentary series, Life.
If you thought that was remarkable, just wait until you hear about the Greater Bowerbird of northern Australia! The male creates two parallel walls of sticks which form a bower with an avenue between the walls. The avenue opens up to a collection of grey stones, shells and bones called the court or gesso. This extravagant structure has no use but to attract potential mates. Using elaborate vocal mimicry, a male entices females to inspect his bower. Upon the arrival of a female in the centre of the bower avenue, the male stands in the court just out of the female’s field of view. The male then displays to her a variety of colourful objects and the colourful patch of feathers on the crest of his head. If the female is sufficiently impressed, mating occurs shortly thereafter.
Bower with avenue opening into the court. Image by Laura Kelley.
The Greater Bowerbird stands apart from its bowerbird relatives because of how it arranges objects in its court. In 2010, researchers at Deakin University looked at the geometry of the Greater Bowerbird court. They discovered that males are very particular with the selection and location of objects in the court. Males create a size gradient of objects in the court by placing smaller objects close to the female’s location in the avenue and increasing the size of the objects placed further away. From the female’s position in the avenue an illusion called forced perspective is created where the pattern in the court appears to be more even than it otherwise would appear.
Measuring the characteristics of the court. Note the progression in size of the objects, small to large from right to left. Image by Laura Kelley.
On January 20th another study was published which found that this illusion impacts mating success! Males who create a court with a higher quality gradient gain more mates than males who make a poorer quality gradient. When observed from the female’s perspective, males with the most evenly patterned courts have the greatest number of mates.
The authors suggest several reasons to explain this phenomenon, but what I find most interesting are the implications. Many animals, especially birds, are very perceptive. There are countless species which perform elaborate courtship rituals. It is very possible that similar forced perspective illusions are used by other species. We may have barely scratched the surface on this one!
Sources:
Anderson, B. L. Bird-Brained Illusionists. Science 335, 292-293 (2012).
Davies, E. Male bowerbirds ‘benefit from optical illusions’. BBC Nature online. Accessed January 20, 2012.
Endler, J. A., Endler, L. C. & Doerr, N. R. Great bowerbirds create theaters with forced perspective when seen by their audience. Current biology 20, 1679-1684 (2010).
Kelley, L. A. & Endler, J. A. Illusions Promote Mating Success in Great Bowerbirds. Science 335, 335-338 (2012).
Visual illusion the key to Bowerbirds mating success. Youtube video. Accessed January 20, 2012.
