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.

Electro-olfactograms (EOGs) were used to assess olfactory responding by aquatic larval and terrestrial adult tiger salamanders (Ambystoma tigrinum) to airborne volatile compounds, and volatile and non-volatile compounds in aqueous solution. Both forms of salamander showed saturation effects to presentations of airborne stimuli (Fig. 2). Saturation was not observed, however, to stimulus presentations in aqueous solution (Figs. 2, 3). When threshold values and concentration-response curve parameters were compared, non-volatile amino acids in solution were more potent stimuli for larvae while airborne volatiles were more potent stimuli for adults (Tables 1, 2). We infer that metamorphosis in the tiger salamander is accompanied by changes in olfactory response characteristics, due possibly to changes in receptor population, changes in perireceptor properties (e.g. mucus) or to changes in stimulus access.

Trigeminal receptors can respond to a wide variety of chemical stimuli, but it is unknown whether these receptors mediate discrimination between chemical stimuli matched for equal perceptual intensity. The present electrophysiological and behavioral experiments address this issue using tiger salamanders, Ambystoma tigrinum, and four compounds (amyl acetate, cyclohexanone, butanol, and d-limonene). In addition, the relative sensitivities of the trigeminal and olfactory systems to these compounds are compared. In electrophysiological cross-adaptation experiments (amyl acetate vs cyclohexanone; butanol vs d-limonene), there was complete cross adaptation such that only concentrations above the background (cross-adapting) stimulus concentration elicited responses, suggesting that chemical stimuli may stimulate trigeminal receptors nonspecifically. In behavioral experiments (amyl acetate vs cyclohexanone; butanol vs d-limonene), only animals with intact olfactory nerves could discriminate between perceptually equivalent concentrations, that is concentrations that elicited the same level of responding. Both electrophysiologically and behaviorally, the trigeminal system exhibited higher thresholds than the olfactory system. We conclude that trigeminal chemoreceptors, at least in salamanders, are unable to discriminate between these two pairs of compounds when matched for equal perceptual intensity, and that trigeminal chemoreceptors are less sensitive than olfactory receptors.

Certain unconditioned stimuli (UCS) in flavor avoidance learning sometimes become ineffective after pairings with relatively stronger UCS. This failure of avoidance learning (avfail) has been demonstrated only with rodents. The present investigations were conducted to determine whether avfail might also occur with avian species, the food selection of which is guided primarily by visual cues. In Experiment 1, starlings were given pairings of methiocarb (a relatively weak UCS) and LiCl (a relatively strong UCS). In Experiment 2, red-winged blackbirds were given pairings of two concentrations of methiocarb (relatively weak and relatively strong UCS, respectively). Pairings were followed by a conditioning trial (UCS gavage in the presence of a color cue) and two-choice tests. Conditioned avoidance was always observed except (a) when methiocarb preceded LiCl and (b) when the low preceded the high methiocarb dose in preconditioning pairings. Experiment 3 demonstrated that UCS habituation could not account for the results of Experiments 1 and 2. The data reflect avfail in the visual modality, and a biological implication of the results is that birds may not learn strong avoidance of aposematic prey containing varied levels of toxicant.Pentobarbital normally elicits weak, eas-sickness (Parker, 1979) that summates ily extinguished conditioned flavor avoid-with the mild sickness normally produced ance, whereas lithium chloride usually is a by pentobarbital. The opposite frequently more effective unconditioned stimulus occurs, and pentobarbital loses its capacity (UCS). When pentobarbital precedes LiCl to produce any measurable flavor avoidance administration, one reasonable prediction (Revusky, Taukulis, Parker, & Coombes, (Revusky, Taukulis, & Peddle, 1979) is that 1979; Revusky, Taukulis, & Peddle, 1979). pentobarbital will become a more effective This phenomenon, termed avfail, has been UCS because it elicits conditioned lithium demonstrated with a number of drug-drug pairings (Revusky, Coombes, & Pohl, 1982)