title: Why do caterpillars whistle at birds? Insect defence sounds startle avian predators.
abstract: Many insects produce sounds when attacked by a predator, yet the functions of these signals are poorly understood. It is debated whether such sounds function as startle, warning or alarm signals, or merely serve to augment other defences. Direct evidence is limited owing to difficulties in disentangling the effects of sounds from other defences that often occur simultaneously in live insects. We conducted an experiment to test whether an insect sound can function as a deimatic (i.e. startle) display. Variations of a whistle of the walnut sphinx caterpillar (Amorpha juglandis) were presented to a predator, red-winged blackbirds (Agelaius phoeniceus), when birds activated a sensor while feeding on mealworms (Tenebrio molitor). Birds exposed to whistles played back at natural sound levels exhibited significantly higher startle scores (by flying away, flinching, and hopping) and took longer to return to the feeding dish than during control conditions where no sounds were played. Birds habituated to sounds during a one-hour session, but after two days the startling effects were restored. Our results provide empirical evidence that an insect sound alone can function as a deimatic display against an avian predator. We discuss how whistles might be particularly effective 'acoustic eye spots' on avian predators.
authors.affiliation: University of Ottawa, School of Psychology, Ottawa, ON K1N 6N5, Canada; Carleton University, Department of Biology, Ottawa, ON K1S 5B6, Canada.
authors.forename: Amanda L
authors.initials: AL
authors.lastname: Dookie
authors.affiliation: Carleton University, Department of Biology, Ottawa, ON K1S 5B6, Canada.
authors.forename: Courtney A
authors.initials: CA
authors.lastname: Young
authors.affiliation: University of Ottawa, Department of Mathematics and Statistics, Ottawa, ON K1N 6N5, Canada.
authors.forename: Gilles
authors.initials: G
authors.lastname: Lamothe
authors.affiliation: Department of Biological Sciences, Virginia Tech, Blacksburg, VA 24061 USA.
authors.forename: Laura A
authors.initials: LA
authors.lastname: Schoenle
authors.affiliation: Carleton University, Department of Biology, Ottawa, ON K1S 5B6, Canada. Electronic address: jayneyack@cunet.carleton.ca.
authors.forename: Jayne E
authors.initials: JE
authors.lastname: Yack
mesh_terms: D000818:Animals; D007915:Lepidoptera; D008297:Male; D046109:Passeriformes; D013216:Reflex, Startle; D014828:Vocalization, Animal
keywords: Acoustic; Avian; Caterpillar; Defence; Deimatic display; Insect; Startle