Why Are Tropical Birds So Colorful? New Study Sheds Light

Mechanisms of Coloration and Study Methods

“For decades, scientists have had this hypothesis that there are brighter or more colorful species of birds in the tropics,” says Chad Eliason, a research scientist at the Field Museum in Chicago and the paper’s lead author. “We wanted to find the mechanism to help us understand these trends– how these bright colors got there and how they spread across the bird family tree over time.”

There are two main ways that color is produced in animals: pigments and structures. Cells produce pigments like melanin, which is responsible for black and brown coloration. Meanwhile, structural color comes from the way light bounces off different arrangements of cell structures. Iridescence, the rainbow shimmer that changes depending how light hits an object, is an example of structural color.

Birds-of-paradise in the Field Museum’s collections. Credit: Kate Golembiewski, Field Museum

Tropical birds get their colors from a combination of brilliant pigments and structural color. Eliason’s work focuses on structural color, so he wanted to explore that element of tropical bird coloration. He and his colleagues combed through photographs, videos, and even scientific illustrations of 9,409 species of birds– the vast majority of the 10,000-ish living bird species known to science. The researchers kept track of which species have iridescent feathers, and where those birds are found.

The scientists then combined their data on bird coloration and distribution with a pre-existing family tree, based on DOI: 10.1038/s41559-024-02487-5