Songbirds get more colourful the closer they live to the equator

WHEN THE Prussian naturalist arrived in South America in 1799, the colours astonished him. “Look at the blossoms, the birds,” he wrote. “Even the crayfish are blue and yellow.”In the intervening centuries, Humboldt’s musings have morphed into an informal, if controversial, hypothesis about the world’s living things: that organisms in equatorial climes are more colourful than those nearer the poles.