Generalization of and Effects of Pre-Exposure on Color-Avoidance Learning by Red-Winged Blackbirds (Agelaius phoeniceus)

Abstract

Abstract We report two experiments designed to assess whether quality of color (and shades) influences food-aversion learning by Red-winged Blackbirds (Agelaius phoeniceus). In Experiment 1, Red-wings were given food paired with one of two shades of red or green followed by toxicant-induced sickness. In subsequent tests for generalization of the learned aversions, avoidance of red was generalized broadly to other shades of red, whereas avoidance of green appeared to be relatively stimulus specific. In Experiment 2, we pre-exposed Red-wings to a single shade of red or green in a feeding context for 4 days. Then the birds were conditioned as in Experiment 1 and tested for expression of learned color aversions. Although pre-exposure weakened expression of aversions to both colors, such effects were more pronounced for green. The effects were greater for birds pre-exposed to the conditioning color in close association with the food than for birds pre-exposed to the conditioning color away from food. Generalization of conditioned aversions and resistance to the effects of pre-exposure may reflect adaptations of Red-wings for prey selection. It would appear adaptive for birds to generalize avoidance learning broadly for conspicuously colored, noxious prey and to exhibit such learning regardless of prior experience with the color. Conversely, because few cryptically colored (e.g. green) prey are noxious, it would be adaptive for learning to be specific for the noxious individuals alone. Finally, we believe that the generalization of learned aversions could serve as a useful criterion in selecting appropriate color stimuli for use in bird control (i.e. repellency) and that the methods presented here could provide one empirical means of assessing such generalizations.