Hummingbirds May Possess a Sensory Superpower

The colors we see are rooted in the retina, specifically in three color cones sensitive to red, green, and blue light. This is known as trichromacy and allows us to see the colors of the rainbow. Red, orange, yellow, green, blue, indigo, and violet are all within our visible range, but so is the color purple. Purple is known as a pure nonspectral color and stimulates red and blue color cones.

Hummingbirds are assumed to have a fourth color cone sensitive to ultraviolet light. This is known as tetrachromacy and allows them to see a wider range of colors, including nonspectral colors such as purple, ultraviolet+red, ultraviolet+green, ultraviolet+yellow, and ultraviolet+purple.

Avian Adventures

To determine if hummingbirds do, in fact, see nonspectral colors, Stoddard and her team set up several bird feeders near the Rocky Mountain Biological Laboratory in Colorado. They performed outdoor experiments over three consecutive summers to understand how hummingbirds use their color vision in real life. Observing them in their natural habitat was important to the study, establishing ecological validity.

Each feeder was equipped with LED tubes that could project two different color types, spectral or nonspectral, and a saucer with either sugar water or plain water. To prevent the hummingbirds from associating a particular location with a reward, researchers swapped the color tubes between trials. They also performed control experiments to help ensure they weren’t using their sense of smell to find the reward.

Over time, the hummingbirds learned to choose the feeder where the sugary water was present, regardless of color type. Because of this, researchers were able to conclude that hummingbirds discern spectral from nonspectral colors, proven by their ability to choose between the two. For example, ultraviolet+green looks different than green to a hummingbird.

A Sensory Superpower

While scientists can only speculate about the way animals perceive color, they’re able to conclude that hummingbirds see things we cannot. Even though visual perception is hard to study, it’s thought that other animals may experience a similar superpower.

Stoddard and her team believe their results could apply to other birds, as well as fish, reptiles, and invertebrates. They realize they’re only scratching the surface of understanding nature’s visual capabilities and it seems there’s still much to learn.