Comparative assessment of food preferences and aversions acquired by blackbirds via observational learning

-Red-winged Blackbirds (Agelaius phoeniceus) can acquire food preferences and aversions merely by observing conspecifics. In Experiment 1, red-wings were trained to prefer or avoid food paired with yellow, as conspecifics watched. After training, all birds were given two-choice tests between food paired with yellow or green for 12 days. Trainers were tested in visual isolation, whereas watchers were tested either in visual isolation or in visual contact with birds who had observed the opposite behavior during training. Food aversions were more resistant to extinction than food preferences (P < 0.05), and, among watchers, social cues facilitated avoidance (P < 0.05). In Experiment 2, red-wings were trained to avoid food paired with yellow, as Common Grackles (Quiscalus quiscula) and red-wings watched, or vice versa, and then two-choice tests were given between yellow and green. Both grackles and red-wings exhibited observational learning, regardless of the training species (P's < 0.05). Social interactions among avian predators may influence how predator abundance affects the Batesian model-mimic complex. We speculate that avoidance learning, which occurs when a predator observes the ingestion of a model, is stronger than preference learning, which occurs when a mimic is ingested. Relatively few models would be needed for the model-mimic complex to operate successfully, and the number of mimics could exceed the number of models without jeopardizing the mimetic advantage. Received 4 November 1983, accepted 12 March 1984. RED-WINGED Blackbirds (Agelaius phoeniceus) can learn food preferences and aversions by observing conspecifics feed and without necessarily ingesting food themselves (Mason and Reidinger 1981, 1982a). Such observational learning is guided by the visual characteristics of the food (Mason and Reidinger 1983a), although tactile and gustatory stimuli, as well as the long-term consequences of ingestion, may become important. Such findings are consistent with results obtained from other species (Klopfer 1959, Duecker 1976). Regarding preferences, Common Chaffinches (Fringilla coelebs), for example, are more likely to commence feeding and to sample new foods when exposed to conspecifics doing so (Rubenstein et al. 1977). White Wagtails (Motacilla alba) and Tennessee Warblers (Vermivora peregrina) behave in a similar fashion (Davies 1976, Tramer and Kemp 1979), and European Starlings (Sturnus vulgaris) may increase feed' The third author is assigned to the Monell Chemical Senses Center from the U.S. Fish and Wildlife Service, Denver Wildlife Research Center, Section of Supporting Sciences, Building 16, Federal Center, Lakewood, Colorado 80225 USA. ing efficiency while minimizing energy expenditure through social feeding (Hamilton and Gilbert 1969). This social feeding is discriminative, and individuals in the flock tend to choose foods that other birds in the flock are choosing (Murton 1974, Williamson and Grey 1975). Regarding aversions, many insectivorous species learn to avoid visual stimuli associated with prey whose ingestion has sickened them (e.g. Brower 1958a, b, c; Duncan and Sheppard 1965; Wickler 1968; Morell and Turner 1970; Rettenmeyer 1970). Some investigators have suggested that observational avoidance learning may also have implications for Batesian mimicry (e.g. Alcock 1969a, b), a phenomenon in which predators learn to avoid noxious prey by developing conditioned aversions (Mason et al. 1982) and generalize this learning to mimics of the unpalatable items. One such implication is that predator pressure on prey, at least in some instances, may not increase linearly with the number of predators. Instead, social interactions among predators may ultimately determine how predator abundance affects the Batesian complex (Avery 1983). An unanswered question relevant to this issue is 796 The Auk 101: 796-803. October 1984 This content downloaded from 157.55.39.163 on Wed, 21 Sep 2016 05:51:28 UTC All use subject to http://about.jstor.org/terms October 1984] Blackbird Observational Learning 797 the strength (i.e. resistance to extinction) of observationally learned aversions in comparison with similarly acquired preferences. Avian predators are likely to observe attacks by conspecifics on both models and mimics, and, in some cases, observed attacks on mimics should exceed observed attacks on models, because mimics are more numerous (Brower 1960). In the former case, the observer should learn approach, or preference, but, in the latter instance, learned avoidance, or aversion, should accrue. In Experiment 1, we assessed which sort of observational experience would exert greater control over behavior.