Hummingbirds can smell their way out of danger

In less time than it takes to read this sentence, hummingbirds can catch a whiff of potential trouble. That is the result of new University of California, Riverside research showing, contrary to popular belief, these tiny birds do have an active sense of smell.

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. In addition, flowers pollinated by birds generally do not have strong odors, unlike those pollinated by insects. For these reasons, scientists did not previously believe the birds possessed the ability to smell things. 

University of California, Riverside scientists funded by the U.S. National Science Foundation have shown 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. A paper describing the experiments is published in Behavioral Ecology and Sociobiology. 

"This is pretty exciting, 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," said Erin Wilson Rankin, a study co-author.

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. 

Rankin said the study raises new questions about the underrated importance that scent plays in birds' foraging decisions and specifically, hummingbird foraging. 

"This study demonstrates the varied and complex mechanisms hummingbirds use in finding food," said Elizabeth Blood, a program director in NSF’s Division of Environmental Biology.