Food Calls in Common Marmosets, Callithrix jacchus, and Evidence That One Is Functionally Referential

SIMPLE SUMMARY: We studied the calls that are made by common marmosets when they see food and when they consume it. They were tested with two types of fruit (banana and blueberries) and two types of insect (live mealworms and crickets). All of these foods elicited Call A, described previously as a food call. Call B was softer and was given more often to crickets. Of particular interest was our discovery of Call C, which was produced when the marmosets discovered insects but not fruit. We showed that Call C has referential meaning, by playing recordings of the call to marmosets when they were eating banana, as follows: on hearing Call C, but not Call A, they stopped eating the banana and went to look in container where they had found insects before. Call C, therefore, has specific meaning, signaling the availability of insect food. All of the calls were produced more frequently when the marmosets were tested alone than when in pairs, indicating that they advertise the availability of food to companions. Call C, at least, is not merely an automatic response reflecting the marmoset’s emotional state. A meaningful call about the discovery of insect food would be essential for survival, since marmosets often forage out of sight of each other. Knowledge of their vocal communication can improve the care of marmosets held in captivity. ABSTRACT: We studied three calls of common marmosets, Callithrix jacchus, elicited in the context of food. Call A, but not B or C, had been described previously as a food call. We presented insects (live mealworms or crickets) and fruit (banana or blueberries) and used playbacks of calls. We found that Call C was produced only in response to seeing insects, and not fruit; it consistently signaled the availability of insects (includes mealworms), and more so when this food could be seen but not consumed. Playback of Call C caused the marmosets to stop feeding on a less preferred food (banana) and, instead, go to inspect a location where mealworms had been found previously, providing evidence that it has referential meaning. No such immediate response was elicited on hearing Call A or background noise. Call A differed from C in that it was produced more frequently when the marmosets were consuming the food than when they could only see it, and call A showed no specificity between insects and fruit. Call B was emitted less frequently than the A or C calls and, by the marmosets that were tested alone, most often to crickets. An audience effect occurred, in that all three calls were emitted more often when the marmosets were tested alone than when in pairs. Recognition of the functional significance of marmoset calls can lead to improved husbandry of marmosets in captivity.