CONTROL OF VOCAL REPERTOIRE BY REWARD IN BUDGERIGARS (MELOPSITTACUS-UNDULATUS)

The calls of some bird species may be modified by reward and punishmen t. However, the operant control of vocal topographies (i.e., the effec t of reward or punishment on the physical dimensions of a vocal respon se) in such species has not been extensively explored. Using a compute r-based, real-time system for rewarding vocalizations with food, the a uthors placed 3 budgerigars under a frequency-dependent reward schedul e. During a session, the budgerigars received food for each vocalizati on that differed from the last N rewarded vocalizations. It was found that each of the budgerigars adapted their vocalizations to this proce dure. When the value of N was 1 or 2, the birds ''solved'' the frequen cy-dependent schedule by developing N + 1 call types and used a simple ''win stay, lose switch'' sequencing strategy. At N = 3, 1 of the bir ds again produced N + 1 (i.e., 4) call types, and another solved the c riterion 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 fr om the previous experimental call repertoire.