Relative frequency of food-related call types within natural call sequences given to high and low-value foods by bonobos at Twycross Zoo and the corresponding playback stimuli.

The values are calculated for the first four calls only; with mean values produced by three individuals in subgroup A (KK, KT, BK) and three other individuals in subgroup B (DT, CK, KH). Results mirror what was previously described from a larger data set from two groups in San Diego (31) showing that although all calls were produced at least once in the high and low contexts, their relative frequency varies with food preference. Barks are produced most typically in response to high value foods; peeps occur often to high value foods, peep-yelps are produced more often to medium-lower value foods, while yelps were typically produced the lower value foods. Grunts were rarely produced in natural call sequences at Twycross, with only 2 individuals producing them, both for low value foods.