How an enzyme powers parrots’ colorful plumage

Parrots’ plumage dazzles with feathers in fiery reds, ostentatious oranges, luminous yellows, and verdant greens. Scientists have now discovered the molecular mechanism that controls these four colors in parrot feathers—a finding that could indicate why the birds have evolved such vivid hues.

Birds like cardinals get their colorful plumage from carotenoids in their diets. But the colors in parrots’ plumage comes from chemicals known as psittacofulvins.

“Parrots are the only birds that we know of that make bright colors in this way,” says Joseph C. Corbo, a scientist at Washington University School of Medicine in St. Louis who led the study, along with the University of Porto’s Miguel Carneiro, Pedro M. Araújo, and Roberto Arbore. Corbo says psittacofulvins differ from carotenoids in that parrots synthesize psittacofulvins endogenously instead of making them from food. “So the bird builds them from basic components,” he says.

Using genetic mapping, biochemical assays, and single-cell genomics, the researchers discovered that the enzyme aldehyde dehydrogenase family 3 member A2 (ALDH3A2) oxidizes psittacofulvins to change their hues from red to yellow. Reds arise from psittacofulvins with an aldehyde end group, and yellows come from psittacofulvins with a carboxylic acid end group. A mixture of the two produces oranges, and yellow psittacofulvins blend with structural blue coloration to give greens (Science 2024, DOI: 10.1126/science.adp7710).

“For a century, scientists puzzled over the mechanisms that enable parrots to produce red or yellow coloration, even as the genes that control melanin, carotenoid, and even structural coloration were discovered,” Geoffrey Hill , who studies bird coloration at Auburn University and was not involved in the research, says in an email. “Now, we finally have an answer.”

ALDH3A2 is broadly expressed, even in humans. It is required for certain metabolic processes, such as converting fatty aldehydes into fatty acids. That parrots have co-opted the enzyme for feather coloration could hint at its role in the birds’ evolution, Corbo says. Male parrots tend to be more brightly colored than females, and females prefer males with brighter colors. Some scientists think the dazzling hues could indicate those males are better at detoxifying fatty aldehydes—although that has not yet been demonstrated.