Hormonal profiles of captive individuals show that bottlenose dolphins (Tursiops spp.) are seasonally polyoestrous, but little is known of reproductive behaviour among free-ranging bottlenose dolphins. In Shark Bay, Western Australia, we have documented for the first time patterns of female attractiveness that may correspond to multiple oestrous cycles. Male bottlenose dolphins in stable alliances of 2-3 individuals form temporary consortships with individual females. Consortships often are established and maintained by aggressive herding. Consortships are associated with reproduction and are a useful measure of a female's attractiveness. Following reproduction, females may become attractive to males when their surviving calf is about 2-2.5 years old or within 1-2 weeks of losing an infant. Individual females are attractive to males for variable periods extending over a number of months, both within and outside of the main breeding season. The duration of attractive periods is greater during breeding season months than during the preceding months. Males sometimes are attracted to females for periods exceeding the reported duration of rising estrogen levels during the follicular stage of the oestrous cycle. Males occasionally have consorted or otherwise been attracted to females in several unusual contexts, including late pregnancy, the first two weeks after parturition, and the day after the loss of a nursing infant. Individual females were consorted by up to 13 males during the season they conceived, supporting predictions of a promiscuous mating system in bottlenose dolphins. Thus, consorting is a strategy by males to monopolize females, but not a completely successful one. Multiple cycling by female bottlenose dolphins may be a strategy to avoid being monopolized by particular males. Given the duration and agonistic nature of many consortships, the benefits to females of such a costly strategy are not obvious. Multiple cycling may reduce the risk of infanticide by males or allow females to mate with preferred males after being monopolized by less desirable males.