Hummingbird at a Feeder (Terry W. Johnson)

By Terry W. Johnson

When I tell you hummingbirds can smell, I am not saying they possess an odor resembling a pair of dirty socks. Instead, I am referring to biologists learning in recent years that hummers have a sense of smell.

Since hummingbirds are such amazing birds it stands to reason, their senses are finely tuned to their environment. In most cases, that is indeed the case. Their excellent eyesight enables them to spot danger and locate flowers containing nectar, tiny insects and potential predators. Their hearing is so acute that they can hear the sounds made by insects pollinating flowers. This enables them to home in on potential sources of nectar.

Their sense of taste enables them to distinguish the sugar content of nectar and thereby concentrate their feeding on flowers laden with the most sugar. They use their sense of touch to navigate among myriads of flowers and other objects.

However, it has long been generally accepted that hummingbirds do not have a sense of smell. There were a couple of reasons for this. First, the olfactory lobes (the area of the brain that controls the sense of smell) in a hummingbird’s brain are very small. In addition, biologists have never been able to demonstrate that hummingbirds display preferences for the scent of flowers containing nectar.

However, the widely held belief that hummingbirds cannot smell was debunked in a study conducted by researchers at the University of California, Riverside. The research was funded by the National Science Foundation and published in Behavioral Ecology and Sociobiology in 2021. “This is pretty exciting,” co-author Erin Wilson Rankin said, “as it is the first clear demonstration of hummingbirds using their sense of smell alone to make foraging decisions and avoid contact with potentially dangerous insects at a flower or feeder.”

The researchers were able to reach this conclusion through a simple study design. Using two identical feeders, they let 100-plus hummingbirds choose between a feeder containing only sugar water and another containing sugar water laced with a chemical scented to indicate the presence of an insect.

The chemicals used were, one, a formulation that European honeybees leave when they visit flowers (the chemical deters other bees from visiting the blooms); two, an attraction chemical generated by Argentine ants; and three, formic acid. The acid is harmful to mammals and birds.

Referring to the acid, Rankin said, “If a bird has any exposed skin on their legs, formic acid can hurt, and if they get it in their eyes, it isn’t pleasant. It’s also extremely volatile.”

The hummingbirds clearly avoided the chemicals produced by the ants and showed a strong aversion to the formic acid. Surprisingly, however, they displayed no reaction to the honeybee scent.

To ensure the birds were reacting to the chemicals themselves and not simply fear of an unfamiliar scent, the biologists tested the birds’ reaction to a common additive to human food named ethyl butyrate. This substance does not exist in the natural world. To us, it smells very much like Juicy Fruit gum. While Rankin admitted she didn’t enjoy the smell, “The birds did not care about it … and didn’t go out of their way to avoid it.”

According to Elizabeth Blood, a program director with the National Science Foundation’s Division of Environmental Biology, the study “demonstrates the varied and complex mechanisms hummingbirds use in finding food.”

As is always the case, whenever the results of a research project upend a popular belief, or answers what appears to be an imponderable question, the research raises new questions. For example, in the case of hummingbirds, one cannot help but wonder how many other things these birds can smell. It would also be interesting to know how their sense of smell further affects their ability to compete with other nectar feeders for food.

It is amazing how much we have learned about hummingbirds during the last few decades. I cannot wait to see what secrets researchers will unlock next.

Terry W. Johnson is a retired Nongame program manager with the Wildlife Resources Division and executive director of The Environmental Resources Network, or TERN, friends group of the division’s Nongame Conservation Section. (Permission is required to reprint this column.) Learn more about TERN, see previous “Out My Backdoor” columns, read Terry’s Backyard Wildlife Connection blog and check out his latest book, “A Journey of Discovery: Monroe County Outdoors.”