Are birds in agricultural habitats attracted to plant volatiles?

Sammanfattning: Birds’ ability to fly allows them to track resource abundance and relocate themselves to areas with more resources. It has been a longstanding belief that they forage mainly through visual cues due to their relatively small olfactory bulbs. However, a growing body of results show that birds use olfaction for communication, when choosing nesting material and detecting predators. Insectivorous birds can during foraging use herbivore-induced plant volatiles to identify infected trees, and have a preference for olfactory cues over visual cues. Induced plant volatiles are released during herbivorous attack as an indirect defense, attracting predatory arthropods and birds which are natural enemies of the herbivores. Birds, however, act also as top predator, meaning they prey on intermediate predators, thus releasing pest from suppression by predatory arthropods. The possibility that these birds use herbivore-induced plant volatiles to localize predatory arthropods have not yet been investigated, which is the aim of this study. We tested the attraction of birds to a common volatile compound, methyl salicylate (MeSa), and evaluated the importance of visual and olfactory cues in a three-way choice experiment in crop fields. Birds could choose between MeSa, neutral odor and no odor in three experimental setups: visible food, invisible food and artificial prey. Overall visits to all setups showed a slight preference for MeSa, with no difference between visible or hidden food. There was however a preference for visual cues when MeSa was presented without any food, next to a dish with odorless artificial prey. We observed that only certain species approached the experiment, mainly corvids and thrushes, thus our conclusions are limited to these taxa. Our results suggest that olfaction might be important for birds foraging in farmland habitats and could also influence the role of birds as biological pest control agents.