title: Aposematism: balancing salience and camouflage.
abstract: Aposematic signals are often characterized by high conspicuousness. Larger and brighter signals reinforce avoidance learning, distinguish defended from palatable prey and are more easily memorized by predators. Conspicuous signalling, however, has costs: encounter rates with naive, specialized or nutritionally stressed predators are likely to increase. It has been suggested that intermediate levels of aposematic conspicuousness can evolve to balance deterrence and detectability, especially for moderately defended species. The effectiveness of such signals, however, has not yet been experimentally tested under field conditions. We used dough caterpillar-like baits to test whether reduced levels of aposematic conspicuousness can have survival benefits when predated by wild birds in natural conditions. Our results suggest that, when controlling for the number and intensity of internal contrast boundaries (stripes), a reduced-conspicuousness aposematic pattern can have a survival advantage over more conspicuous signals, as well as cryptic colours. Furthermore, we find a survival benefit from the addition of internal contrast for both high and low levels of conspicuousness. This adds ecological validity to evolutionary models of aposematic saliency and the evolution of honest signalling.
authors.affiliation: School of Biological Sciences, University of Bristol, Bristol Life Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK j.barnett@bristol.ac.uk.
authors.forename: James B
authors.identifier: 0000-0001-9789-4132
authors.initials: JB
authors.lastname: Barnett
authors.affiliation: School of Experimental Psychology, University of Bristol, 12a Priory Road, Bristol BS8 1TU, UK.
authors.forename: Nicholas E
authors.initials: NE
authors.lastname: Scott-Samuel
authors.affiliation: School of Biological Sciences, University of Bristol, Bristol Life Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK.
authors.forename: Innes C
authors.initials: IC
authors.lastname: Cuthill
mesh_terms: D000818:Animals; D001362:Avoidance Learning; D005075:Biological Evolution; D000067558:Biological Mimicry; D001717:Birds; D003116:Color; D011235:Predatory Behavior
keywords: aposematism; camouflage; defensive coloration; honest signalling; visual signalling; warning signals