Pretty pollies break evolutionary rules

One of the longest standing puzzles in the world of the study of birds has been solved by a team of scientists from ANU and the University of California at Santa Barbara.

Led by Dr Rob Heinsohn from the Centre for Environmental and Resource Studies, the group has discovered why a species of parrot from northern Australia breaks the ornithology mould, as detailed in a paper in the leading international journal Science.

“In the bird world, brilliant plumage is typical of male birds who use their colours to attract mates or repel rivals, whereas females tend to have drab colours to help them avoid detection by predators while they are nesting,” Dr Heinsohn says.

“But in a handful of bird species the sex roles have been reversed and females have brighter colours. Eclectus parrots, which are found in the rain-forests of the Cape York Peninsula, follow neither of these patterns.

“The red female and shiny green male eclectus parrots look so different from each other that they were long thought to be separate species. They pose a dilemma for evolutionary biologists because the two sexes appear equally bright, yet their colours have diverged so dramatically.”

Dr Heinsohn and his team found that there is an unusual role reversal in the eclectus parrot species compared to many other species of bird. While the male parrots gather food, it is the females that protect the nest.

“The female eclectus parrot spends virtually all year defending scarce nest hollows high in the rainforest canopy. They may fight to the death with other parrots to defend their hollow and chicks,” Dr Heinsohn says.

“Their 100 per cent attendance at the nest is only possible because the males do all of the foraging, and regurgitate the fruit to the females at the nest hollow.”

The team used spectrometry to analyse the colours of the eclectus parrots on Cape York Peninsula and found that the females’ bright red was used as a signal to other parrots that their hollow was occupied.

The male birds’ green, on the other hand, provides good camouflage from hawks when they are foraging in the rainforest canopy, but is also very bright at the nest hollow where they compete with other males.

“There is no other bird in which males and females look so different,” Dr Heinsohn says.

“Our work shows that bright colours can arise independently in either sex depending on the extent of competition among the sexes and how much the lifestyles of males and females differ.”

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