Where would you go to bask in nature's most dazzling colours?
Many of us would head for the tropics. Since the 1800s, explorers have waxed lyrical about the dazzling colours of tropical wildlife. From parrots and butterflies to orchids and birds-of-paradise, tropical animals display bold tapestries of turquoise on red or blue on orange: an "extreme richness of colour", according to the naturalist Alfred Russel Wallace.
But we might be wrong about this. A new study flies in the face of popular belief and concludes that temperate wildlife is more colourful than tropical.
Rhiannon Dalrymple compared the colours of different groups of wildlife during her PhD at the University of New South Wales in Sydney, Australia. She has since moved to Hamline University in Saint Paul, Minnesota.
"When we started, I thought I would just be proving an old idea," says Dalrymple.
Earlier studies were contradictory, but each study only tested a narrow set of wildlife and only looked at colours that humans see.
Dalrymple and her colleagues compiled a list of 1,333 species of native birds, butterflies and flowers along the eastern coast of Australia, down as far as Tasmania. Their sample spans 34.5° of latitude and includes tropical rainforests, temperate woodlands and shrublands.
They recorded their colours of all the species, including ultraviolet light, and noted where they lived. Then they checked whether the colours were more intense in the tropical regions, if they were more contrasting, or if there was a greater range of colours on display.
They found that colouration hardly changed at all from north to south.
Both Dalrymple and Adams had to use museum collections to get enough specimens
But there was weak evidence that wildlife further away from the tropics sported more colours, and that the colours were also more intense with bigger contrasts.
The results have been published in the journal Global Ecology and Biogeography.
"We have flipped people's views," says Dalrymple.
Not everyone is convinced. The study is focused on eastern Australia, and it is a "big jump" to assume that the patterns there apply to the rest of the world, says Jonathan Adams of Seoul National University in South Korea.
In a study published in 2014, Adams examined 247 butterfly species and found that those in tropical Ecuador were more colourful than those in subtropical Florida and temperate Maine. He says that his study covered both ever-wet tropics and more severe temperate climates, whereas Dalrymple's Australian study only "touches mild winters and the fringes of subtropics".
Adams says he wants to "keep an open mind"
Both Dalrymple and Adams had to use museum collections to get enough specimens for their studies. But those collections might be biased towards more colourful organisms.
That's because many came from professional collectors who made a living selling their specimens, and these collectors tended to ship more colourful specimens than drab ones. That's understandable: a jambu fruit dove, with its plum-red head and jade-green plumage, brightens up a room more than a brownish-grey zebra dove.
"Biases in collections could have affected how Europeans perceived colours of tropical animals," says Dalrymple.
For now, Adams says he wants to "keep an open mind" about whether the tropics really are more colourful.