Supply and demand predict male grooming of swollen females in captive chimpanzees, Pan troglodytes

► Captive female chimpanzees receive more and give less grooming to males when swollen. ► The market value of oestrous female chimpanzees varies according to their availability. ► Males groom swollen females less as the availability of swollen females increases. ► Higher ranking males groom swollen females less than lower ranking males.