Attraction to Smelly Food in Birds: Insectivorous Birds Discriminate between the Pheromones of Their Prey and Those of Non-Prey Insects

SIMPLE SUMMARY: The role of olfaction in avian life histories has traditionally been neglected, but a growing body of evidence suggests that birds use olfaction in different biological contexts, including foraging. Insectivorous birds are known to detect the defence volatiles emitted by trees when attacked by herbivore arthropods. Recently, it has been shown that insectivorous birds not only use these indirect cues to locate their prey but that they can also eavesdrop on the pheromones emitted by the prey. However, the questions of whether avian attraction is limited to prey pheromones only or whether they can detect any insect pheromone remain unexplored. Therefore, we performed a field experimental study using artificial larvae close to pheromone dispensers placed on trees to analyze whether birds are attracted to prey pheromones but not to non-prey pheromones or control unscented dispensers. We recorded the number of trees that contained artificial larvae with signals of avian predation and found that insectivorous birds were only attracted to prey pheromones, confirming that insectivorous birds are able to eavesdrop on prey pheromones and suggesting that birds are not attracted to non-prey pheromones. ABSTRACT: Natural selection has favored the evolution of different capabilities that allow animals to obtain food—e.g., the development of senses for improving prey/food detection. Among these senses, chemical sense is possibly the most ancient mechanism used by organisms for environmental assessment. Comparative studies suggest the prime role of foraging ecology in the evolution of the olfactory apparatus of vertebrates, including birds. Here, we review empirical studies that have shown birds’ abilities to detect prey/food via olfaction and report the results of a study aiming to analyze the specificity of eavesdropping on prey pheromones in insectivorous birds. In a field study, we placed artificial larvae and a dispenser with one of three treatments—prey (Operopthera brumata) pheromones, non-prey (Rhynchophorus ferrugineus) pheromones, or a control unscented dispenser—on the branches of Pyrenean oak trees (Quercus pyrenaica). We then measured the predation rate of birds on artificial larvae. Our results show that more trees had larvae with signs of avian predation when they contained a prey pheromone dispenser than when they contained a non-prey pheromone dispenser or an unscented dispenser. Our results indicate that insectivorous birds can discriminate between the pheromones emitted by their prey and those emitted by non-prey insects and that they only exhibit attraction to prey pheromones. These results highlight the potential use of insectivorous birds in the biological control of insect pests.