Have you ever seen a beautiful red cardinal in your backyard? This bird is so striking that seven states list it as their state bird. Red coloration is not that common in nature, seen mainly in flowers and birds and some fur colors.

Students can learn about this phenomenon by completing this reading and CER worksheet.

The red color of cardinals primarily comes from the foods they consume, which are rich in carotenoids. Carotenoids are pigments found in plants, fruits, and insects that cardinals eat as part of their diet. These pigments are responsible for the vibrant red coloration seen in the feathers of male cardinals.

The mechanism is complex and involves several intermediaries. This short explanation is based on a study from Nature with a simplified graphic to illustrate how enzymes are involved. Washington University also has a great article about cardinals and their coloration.

There are several genes that work together to express red coloration. These genes code for proteins that can convert yellow carotenoids to red carotenoids.

Students read about the study and examine the graphic to understand how the mechanism works to express red coloration. This is a great introduction to genes and evolution. Red coloration is generally thought to be the result of sexual selection. Birds with red feathers are more likely to find mates and pass those genes to their offspring. Questions about the article and graphic follow the CER format (claim, evidence, reasoning.)