Direct and Observational Learning by Redwinged Blackbirds (Agelaius Phoeniceus): The Importance of Complex Visual Stimuli
J. Russell Mason U.S. Department of Agriculture, Animal and Plant Health Inspection Service,
Denver Wildlife Research Center c/o Monell Chemical Senses Center, Philadelphia Pennsylvania.
Redwing blackbirds ( Agelaius phoeniceus, Mason & Reidinger, 1983a), European starlings ( Sturnus vulgaris, Schuler, 1980), house sparrows ( Passer domesticus; Greig-Smith & Rowney, 1987), and a variety of other avian species (e.g., Japanese quail, Corturnix japonica; Czaplicki, Borrebach, & Wilcoxin, 1976) learn to avoid visual cues associated with sickness. For redwings, visual stimuli appear relatively more important than taste in avoidence acquisition ( Mason & Reidinger , 1983a), and certain colors seem to be more effective conditioned stimuli than others. For example, avoidance generalization is broad for hues of red, but relatively narrow for hues of green ( Mason & Reidinger, 1983b). Ecologically, the differential effectiveness of color is predictable, since red is used frequently by animals to advertise unpalatability ( aposematic coloration; Terhune, 1977). Green serves this function rarely, if ever, and is more often associated with the cryptic coloration used by palatable prey for concealment from predators ( Brower, Cook, & Croze, 1967; Wickler, 1968).
Besides direct acquisition of avoidance, red-wings will learn by observing conspecifics or other birds such as common grackles ( Quiscalus quiscula; Mason, Arzt, & Reidinger, 1984a). Such vicariously acquired avoidance closely resembles avoidance acquired as a function of direct experience. For example, vicarious learning occurs in a single trial, and resistance to extinction is usually similar to