New research findings have revealed that contrary to popular belief, hummingbirds do have an active sense of smell. In fact, scientists say that in less time than it takes to read this sentence, hummingbirds can catch a whiff of potential trouble.
Researchers have known for some time that vultures have a highly sensitive sense of smell, with some species being compared to “airborne bloodhounds.” This is due in part to their large olfactory bulbs — tissue in the brain that controls smell. However, hummingbirds’ olfactory bulbs are, like the rest of their bodies, extremely small. Earlier studies were unable to demonstrate that hummingbirds showed a preference for the smell of flowers containing nectar, so scientists did not previously believe the birds possessed the ability to smell things. But now that has all changed…
Scientists have now demonstrated for the first time that not only can hummingbirds smell insects, but also that scent may help them stay out of danger while looking for nectar to eat.
For their experiments, the researchers allowed more than 100 hummingbirds to choose between two feeders, either sugar water alone, or sugar water plus one of several chemicals whose scent signaled the presence of an insect. There were no visual differences between the two feeders offered in each of the experiments.
Tests included the scent deposited on flowers by European honeybees, an attraction chemical secreted by Argentine ants, and formic acid, a defensive compound produced by some Formica ants which is known to harm birds as well as mammals.
“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.”
-Dr. Erin Wilson Rankin, associate entomology professor and study co-author
The hummingbirds avoided both of the ant-derived chemicals, especially the formic acid. However, they had no reaction at all to the honeybee scent, which is known to deter other bees from visiting flowers.
To ensure it was the chemical itself the birds were reacting to, and not simply a fear of new smells, the researchers did an additional test with ethyl butyrate, a common additive in human food.
“It smells like Juicy Fruit gum, which is not a smell known in nature… The birds did not care about it and didn’t go out of their way to avoid it.”
The study raises new questions about the underrated importance that scent plays in birds’ foraging decisions and specifically, hummingbird foraging. The scientists say that the foraging decisions of hummingbirds help us understand how the ecosystem functions, and any actions that ultimately might be needed for conservation.
Journal Reference: Ashley Y. Kim, David T. Rankin, Erin E. Wilson Rankin. What is that smell? Hummingbirds avoid foraging on resources with defensive insect compounds. Behavioral Ecology and Sociobiology, 2021; 75 (9) DOI: 10.1007/s00265-021-03067-4