“According to this theory, a bright red bird is basically screaming, ‘Look how healthy I am’, ‘My immune system is working’ or ‘My metabolism is working’ or ‘I am so healthy that I can invest pigments in my feathers” said Ms. McCoy. “This study was our attempt to say, is that true? Or have men found a smart way to cheat a bit in the game of life? “

For the new study, Ms. McCoy and her colleagues examined 20 specimens – one male and one female from 10 different Tanager species or subspecies each – in the ornithological collection of the Harvard Museum of Comparative Zoology.

Female tanagers are generally much more boring than their male counterparts, an observation the researchers confirmed using a spectrophotometer, which measures how much light is reflected off a surface. They found that the males had both darker blacks and saturated colors than the females.

So they were surprised when they extracted some of the carotenoid pigments from each sample. Despite their obvious differences in appearance, men and women had roughly similar amounts and types of carotenoid pigment. “I was shocked,” said Ms. McCoy.

One major difference, however, came about when the feathers were placed under a powerful microscope. The feathers of female birds were relatively simple, and cylindrical barbs emerged from the central shaft of the feather. Smaller, thinner filaments called barbules branched directly from each of these barbs.

However, feathers from male birds had much more sophisticated microstructures, with barbs and barbs that were unusually flat, wide, elongated, or protruding at odd angles.

The researchers then used optical modeling software to simulate how light interacted with these unusual spring structures. They found that the microstructures had significant optical effects.