What is that smell? Hummingbirds avoid foraging on resources with defensive insect compounds

Abstract

Hummingbirds utilize visual cues to locate flowers, but little is known about the role olfaction plays in nectar foraging despite observations that hummingbirds avoid resources occupied by certain insects. We investigated the behavioral responses of both wild and captive hummingbirds to olfactory cues of hymenopteran floral visitors, including native wood ants (Formica francoeuri), invasive Argentine ants (Linepithema humile), and European honeybees (Apis mellifera). We demonstrate for the first time that hummingbirds use olfaction to make foraging decisions when presented with insect-derived chemical cues under field and aviary conditions. Both wild and captive hummingbirds avoided foraging on feeders with defensive chemicals of F. francoeuri and aggregation pheromones of L. humile, but showed no response to honeybee cuticular hydrocarbons. Our experiments demonstrate the importance of olfaction in shaping hummingbird foraging decisions. Significance statement Recent reviews reveal that avian olfaction is not just limited to vultures and a few taxa. We demonstrate that a very charismatic group, hummingbirds, avoid defensive and aggregatory chemical cues from insects present at nectar resources. Olfactory cues can provide critical information about the presence and potential threat of insect floral visitors. This study raises new questions about the underrated importance of olfaction in avian foraging and specifically, hummingbird foraging.

Potential effects of artificial feeders on hummingbirds-plant interactions: are generalizations yet possible?

“…The results revealed significant differences in microbial communities, with greater abundance and richness observed in feeders, particularly with higher bacterial turnover across a three-day period, although no significant variation was noted in fungal diversity (Lee et al 2019). This variability was associated with a decline in the frequency of hummingbird visitation over time, indicating the possible existence of a mechanism for detecting 'old nectars' (Lee et al 2019), perhaps because nectar fermentation might produce volatiles that hummingbirds would perceive (Goldsmith & Goldsmith 1982, Kim et al 2021. Additionally, in relation to phoretic mites, which disembark from the hummingbird's beak and move towards the nectar source during the visit, deposition rates increased with sugar concentration in feeders (Márquez-Luna et al 2016).…”