title: Context-dependent decisions among options varying in a single dimension.
abstract: Contrary to theories of rational choice, adding alternatives to a choice set can change the choices made by both humans and animals. This is usually done by adding an inferior decoy to a choice set of two favoured options that are characterized on two distinct dimensions. We presented wild, free-living rufous hummingbirds (Selasphorus rufus) with choices between two or three options that varied in a single dimension only. The options varied in concentration, in volume or in corolla length. When the options varied in concentration, the addition of a medium option to a choice set of a low and a high concentration caused birds to increase their preference for the high option. However, they decreased their preference for the high concentration option when a low option was added to a choice set of high and medium concentrations. When the options varied only in volume, the addition of a high volume option to a choice set of low and medium options decreased the birds' preference for the medium option. We saw no effects of adding a third option when the options varied in corolla length alone. Hummingbirds, then, make context-dependent decisions even when the options vary in only a single dimension although which effect occurs seems to depend on the dimension being manipulated. None of the current theories alone adequately explain these results.
authors.affiliation: School of Psychology, University of St. Andrews, St. Mary's College, South Street, St. Andrews, Fife, Scotland KY16 9JP, UK.
authors.forename: Kate V
authors.initials: KV
authors.lastname: Morgan
authors.forename: T Andrew
authors.initials: TA
authors.lastname: Hurly
authors.forename: Melissa
authors.initials: M
authors.lastname: Bateson
authors.forename: Lucy
authors.initials: L
authors.lastname: Asher
authors.forename: Susan D
authors.initials: SD
authors.lastname: Healy
mesh_terms: D000818:Animals; D001070:Appetitive Behavior / Q000187:drug effects*; D001717:Birds; D003657:Decision Making / Q000187:drug effects*; D019422:Dietary Sucrose / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D008297:Male
chemical_list: D019422:Dietary Sucrose