To dissect the observation, the team designed a new study that allowed hummingbirds to choose between a feeder with plain sugar water and an identical feeder containing sugar water laced with one of three chemicals: cuticular hydrocarbons found on honey bees’ exoskeletons; formic acid, a defense chemical released by Formica ants; and (Z)-9-hexadecenal, the ant aggregation pheromone they’d used in the bee study. The birds avoided feeders that smelled of the latter two, but not those that smelled of honey bees or a common food additive. “For specific contexts such as danger, they are responding to odors that are associated with . . . chemicals produced by insects,” says Wilson-Rankin. “They might not have many [olfactory] neurons, but they use those neurons to avoid dangerous [situations].”
— Ecologist Erin Wilson-Rankin studies olfaction in hummingbirds. Read more in Even the Tiniest of Birds Use Smell in Some Situations at The Scientist.