The calls of some bird species may be modified by reward and punishment. However, the operant control of vocal topographies (i.e., the effect of reward or punishment on the physical dimensions of a vocal response) in such species has not been extensively explored. Using a computer-based, real-time system for rewarding vocalizations with food, the authors placed 3 budgerigars under a frequency-dependent reward schedule. During a session, the budgerigars received food for each vocalization that differed from the last N rewarded vocalizations. It was found that each of the budgerigars adapted their vocalizations to this procedure. When the value of Nwas 1 or 2, the birds "solved" the frequency-dependent schedule by developing N + 1 call types and used a simple "win stay, lose switch" sequencing strategy. At N = 3, 1 of the birds again produced N + 1 (i.e., 4) call types, and another solved the criterion by markedly increasing call variability. New calls developed from the elements of old call types and using multidimensional scaling techniques, the authors traced the evolution of each new call type from the previous experimental call repertoire.

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In this experiment we show that the active time model (ATM) accurately predicts probe data from multiple concurrent VI VI schedules. Subjects were trained under a concurrent VI 30-s VI 60-s and a concurrent VI 60-s VI 120-s schedule. Two types of unreinforced probes were then conducted. The first paired the two VI 60-s stimuli. These stimuli, while equivalent in their associated absolute rates of reinforcement, differed in their relative rates of reinforcement. The second probe paired the VI 30-s stimulus with the relatively rich VI 60-s stimulus. In contrast with the first probe, these stimuli differed in their absolute rates of reinforcement, while being similar in their relative rates. During the first set of probes, birds preferred the VI 60-s stimulus trained with the VI 120-s schedule. During the second set of probes, birds were indifferent to the two stimuli. These results are less extreme than others reported in the literature. Nonetheless, we found that ATM accurately fit individual subject data in both sets of probes. In contrast a variant of scalar expectancy theory did not fit the data at either the individual or group level.

Animals coping with operant conditioning tasks often show behaviors that are not recorded by keys, levers and similar response transducers. Nevertheless, these adjunctive behaviors should not be disposed of by classifying them as incidental. Often they are found to be at least partially influenced by the experimentally programmed contingencies, and under certain conditions they can in turn influence conditioned behaviors. Here we describe the occurrence and characteristics of two such behaviors, stimulus grasping in operantly key-pecking pigeons and intra-delay stereotypies in a delayed matching-to-sample task with budgerigars. It is argued that for a proper account of these behaviors it is necessary to refer to a behavioral systems approach that appeals to longer ranging ontogenetic and phylogenetic histories than is usually considered in the psychological literature. The gaping towards on-key stimuli by pigeons is attributed to the hypothesis that operantly conditioned key-pecks probably relate to a grasp-pecking response that is normally executed towards non-edible items covering food. The intra-delay behaviors shown by the budgerigars are assumed to have originated from stress-induced displacement responses that adventitiously came under the influence of differential reinforcement contingencies. Finally, we discuss what kinds of evidence are needed to put these hypothetical explanations on a more certain footing.

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