The effect of solicitations on grooming exchanges among female Japanese macaques at Katsuyama

In group-living primates, individuals often exchange grooming with not only kin but also non-kin. We investigated the effect of soliciting behaviors on grooming exchanges in a free-ranging Japanese macaque (Macaca fuscata) group at Katsuyama. In this study, we used a focal animal sampling method, targeting 14 females. Data were collected for 15.75 ± 2.67 (mean ± SD) hours per focal female. We classified female–female pairs into three pair types: kin pairs, affiliated non-kin pairs, and unaffiliated non-kin pairs. Females received grooming more frequently when they solicited after grooming their partners than when they did not solicit in all pair types. In addition, females received grooming less frequently when they did not groom their unaffiliated non-kin partners before soliciting; prior grooming was not needed to receive grooming from kin or affiliated non-kin partners. The degree of grooming reciprocity did not differ according to the frequency with which females in kin or affiliated non-kin pairs solicited after grooming. On the other hand, grooming reciprocity between unaffiliated non-kin females was more balanced when they solicited frequently after grooming, as compared with when they did not. In conclusion, our study suggests that soliciting behaviors promote grooming exchanges in female Japanese macaques.