International Journal of Comparative Psychology

Several experiments have shown that engaging in territorial singing is an appetitive and reinforcing activity in gibbons. The present study examined whether the strength of this behavior would vary with changes in motivational conditions in the same manner as does the strength of the consummatory behavior associated with other reinforcers. The subjects were a fully accommodated pair of siamangs. Following baseline. (A" duration = 34.33 min), song-bout durations were observed under low motivation (X = 20.33 min), then high motivation (X= 36.16 min), then low (Z= 22.67 min), then high (X = 32.50 min). Six song bouts were observed under each condition. In the high motivation condition, 5-6 days intervened between song bouts; in the low motivation condition, song bouts were separated by 2 days. Each change in motivation was accompanied by a significant change in song-bout duration (Mann-Whitney t/ tests; p's < .01 ). Findings are related to a general conception of species-typical behavior as a source of reinforcement.