AsianScientist (Mar. 13, 2014) – Researchers have used mathematical models of bird vision to represent the colors of Australian flowers as birds themselves perceive colors. The models showed that a small range of novel colors evolved among bird-pollinated flowers far more often than would occur by chance.
In the study, led by the Monash University School of Biological Sciences Associate Professor Martin Burd, and published in the Proceedings of the Royal Society B, the researchers measured the spectral reflectance of flowers (the wavelengths of light reflected back from petals) of 234 native Australian species of flowers, consisting of 80 bird-pollinated species and 154 insect-pollinated species.
“We humans have three types of color receptors in our retinas, sensitive to blue, green, and red light. However, birds have four types of receptors, so what they see is far more complex than what we see. Even among birds there is variation. Some birds, including Australian honeyeaters, have violet-sensitive receptors along with blue, green and red. Other birds use receptors sensitive to ultraviolet rather than violet light,” he explained.
The researchers translated the spectral reflectance patterns of flowers into single points in a ‘color space’ that represents the sensitivities of the four kinds of color receptors in bird vision.
About half the flowers that were bird-pollinated overlapped with the color space occupied by insect-pollinated flowers. According to Burd the similarity in colors was not surprising, since bird pollination usually evolved from insect-pollinated ancestors.
“The other half of bird-pollinated species, however, were crowded in a narrow and separate stretch that occupied just one per cent of the total volume of the color space. These colors appear red to humans, and we named this cluster the ‘red arm’. Their reflectance profiles would also strongly stimulate the red receptors in bird eyes,” he said.
Burd said the research indicated that many flowering species had evolved to ‘talk’ to birds using a very particular set of color ‘words’.
“In particular, the distinctiveness of the ‘red arm’ appeared only when the color space was based on the visual system of honeyeaters.
“Models of the other visual system in birds with ultraviolet receptors, common in parrots and songbirds, did not reveal a distinctive red arm of floral colors,” he said.
In other words, many bird-pollinated flowers in Australia have evolved into colors that the honeyeaters are visually attracted to. This was not surprising, given that honeyeaters are the main bird pollinators in Australia.
“The birds are talking honeyeater language because that’s where all the action is!” Burd remarked.
The article can be found at: Burd et al. (2014) Distinctive convergence in Australian floral colors seen through the eyes of Australian birds.
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Source: Monash; Photo: Dirk Wallace/Flickr/CC.
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