Researchers Find That Hummingbirds See More Colors Than Humans

Getting a visit from a hummingbird or two always feels special. Whether you have a feeder set up in your yard or some flowering plants that attract them, it's always fun to watch them flit around, buzzing in close for a quick drink before zooming away. There's a lot that makes these beautiful creatures unique; they're one of the smallest birds, they can fly up to 30 miles an hour, and they're the only birds that can fly backward. And recently, scientists discovered one more fascinating attribute that makes them special; they can recognize a variety of colors beyond what humans can see.

In addition to being sensitive to red, green, and blue light (which is what makes up our vision), birds are also sensitive to ultraviolet light. Mary Caswell Stoddard, an assistant professor in the Princeton University Department of Ecology and Evolutionary Biology, along with her research team, wanted to learn how birds see color in the world, so she set up several experiments involving wild broad-tailed hummingbirds at Rocky Mountain Biological Laboratory in Colorado.

The researchers were particularly interested in nonspectral colors, or colors that are created by shades from different ends of the spectrum. Purple is the only nonspectral color that humans can see, because it's created by red and blue light, and doesn't appear in the rainbow. However, birds may see up to five, including purple and combinations with ultraviolet light, such as ultraviolet+red and ultraviolet+yellow.

To study how hummingbirds recognize different colors, the scientists performed outdoor experiments each summer for three years. They started by building LED tubes programmed to display a range of colors, including nonspectral colors. Then, they set up two feeders, each with an LED tube next to it, in a meadow visited by broad-tailed hummingbirds. One feeder had plain water, while the other had sugar water. Each feeder emitted a different color, and the researchers frequently swapped the locations of the two feeders so the hummingbirds couldn't find the sugar water feeder by location alone.

The researchers found that hummingbirds are able to see a variety of nonspectral colors, and can distinguish them from other colors. For example, in one trial, the feeder with plain water emitted green light, while the feeder with sugar water emitted ultraviolet+green light, a nonspectral color. Though the two lights look identical to the human eye, the hummingbirds were able to see a difference between the two, and consistently find the feeder with sugar water, even when it was moved.

Even though this discovery is pretty cool, it doesn't mean you have to set up special feeders in your yard to attract hummingbirds. Despite the fact that they can see more colors than humans, there's no evidence to suggest that the unique shades they see appear any brighter than the normal colors we're used to.

The best way to get hummers to visit your yard is to plant a variety of nectar-rich flowers. Phlox, hollyhock, foxglove, lantana, and butterfly bush are all good choices. Previous research has suggested that these birds are most attracted to the color red (which is why you'll see a lot of feeders in this color), so plants with red blooms might be especially effective at bringing them to your yard. Also, flowers that are almost tube-shaped (such as foxglove) are popular with hummingbirds, because they're perfectly shaped for their long beaks.

You can also set up your own hummingbird feeder to encourage these winged wonders to visit. Just be sure to clean it every three days when the weather's hot to prevent bacteria from growing in the sugar water. With the right plants in your yard and a little luck, you can watch hummingbirds flit around your garden all summer!