Robert M. Seyfarth

'Food' Calls Produced By Adult Female Rhesus (Macaca Mulatta) and Japanese (M. Fuscata) Macaques, Their Normally-Raised Offspring, and Offspring Cross-Fostered Between Species

We tested a recent claim that rhesus and Japanese macaque offspring cross-fostered between species exhibit vocal learning by producing food calls typical of their adoptive rather than their genetic species (MASATAKA & FUJITA, 1989). Our study population consisted of four groups of socially-reared animals housed outdoors - two of each species. Food calls produced by adult female rhesus and Japanese macaques did not differ at the species level, although individual differences were clearly present. Food calls produced by normally raised offspring differed both between individuals and between species. In spite of statistically significant differences, however, immatures in the two species still showed substantial overlap on every acoustic feature that was measured. Evidence from four cross-fostered offspring was equivocal. Two rhesus macaques raised in Japanese macaque social groups produced calls that were typical of their own species. Some measurements from calls produced by two cross-fostered Japanese macaques fell closer to mean values for normal rhesus than for those of their own species. However, these measurements were still within the observed range of variation shown by normally raised Japanese macaques. We conclude that food calling behavior of cross-fostered Japanese macaques may have shown modification, but that any such effect was not based on a species-specific adult model. Given the variability of these sounds and the lack of species differences in adult female vocalizations, food calls do not present a good opportunity to test for vocal learning in cross-fostered rhesus and Japanese macaques.

Animal Communication Networks: Social complexity and the information acquired during eavesdropping by primates and other animals

In many of the studies reviewed in this book, eavesdropping takes the following form: a subject has the opportunity to monitor, or eavesdrop upon, an interaction between two other animals, A and B. The subject then uses the information obtained through these observations to assess A’s and B’s relative dominance or attractiveness as a mate (e.g. Mennill et al., 2002; Ch. 2). For example, Oliveira et al. (1998) found that male fighting fish Betta splendens that had witnessed two other males involved in an aggressive interaction subsequently responded more strongly to the loser of that interaction than the winner. Subjects’behaviour could not have been influenced by any inherent differences between the two males, because subjects responded equally strongly to the winner and the loser of competitive interactions they had not observed. Similarly, Peake et al. (2001) presented male great tits Parus major with the opportunity to monitor an apparent competitive interaction between two strangers by simulating a singing contest using two loudspeakers. The relative timing of the singing bouts (as measured by the degree of overlap between the two songs) provided information about each ‘contestant’s’ relative status. Following the singing interaction, one of the ‘contestants’ was introduced into the male’s territory. Males responded significantly less strongly to singers that had apparently just ‘lost’ the interaction (see also McGregor & Dabelsteen, 1996; Naguib et al., 1999; Ch. 2). What information does an individual acquire when it eavesdrops on others? In theory, an eavesdropper could acquire information of many different sorts: about A, about B, about the relationship between A and B, or about the place of