Studies of dolphin communication have been hindered by the difficulty of localizing sounds underwater and thus identifying vocalizing individuals. Male bottlenose dolphins (Tursiops sp.; speckled form) in Shark Bay, Western Australia produce a vocalization we call 'pops'. Pops are narrow-band, low frequency pulses with peak energy between 300 and 3000 Hz and are typically produced in trains of 3-30 pops at rates of 6-12 pops/s. Observations on the pop vocalization and associated behavior were made as part of a long-term study of bottlenose dolphins in Shark Bay. During 1987-88 seven dolphins, including three males, frequented a shallow water area where they were daily provisioned with fish by tourists and fishermen. The three males often produced pops when accompanied by single female consorts into the shallows. Fortuitously, the males often remained at the surface where pops were audible in air, enabling us to identify the popping individual. All 12 of the female consorts in the study turned in towards males at a higher rate when the males were popping than when they were not popping. All 19 occurrences of one form of aggression, 'head-jerks', were associated with pops. We conclude that pops are a threat vocalization which induces the female to remain close to the popping male during consortships.
Pops are a low-frequency, pulsed vocalization produced by Indo-Pacific bottlenose dolphins (Tursiops cf. aduncus) in Shark Bay, Western Australia and are often heard when male alliances are consorting or ‘herding’ a female. Previous research indicated that pops produced in this context are an agonistic ‘come-hither’ demand produced by males and directed at female consorts. Here we examine pop occurrence during focal follows on bottlenose dolphin alliances with and without female consorts present. Regression analysis was conducted to determine if pop numbers were higher in the presence of female consorts, and if variables including group size alone and the interaction between presence/absence of a consortship and group size, influenced pop production. While the presence or absence of a consortship significantly affected the number of pops, average group size had no significant effect on pop production. Our research provides further evidence that the pop vocalization plays an important role in consortships.
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.
Patterns of association among bottlenose dolphins resident in Shark Bay, Western Australia were analyzed using party membership data. Parties contained an average of 4.8 individuals, but party size and composition were unstable. While these temporary parties often contained both males and females, long term consistent associations generally were between members of the same sex. The highest association coefficients, resulting from very frequent co-occurrence within parties were between males and between mothers and offspring. Males formed subgroups of two or three individuals who consistently associated with each other, and these were stable over periods of at least seven years in some cases. Male subgroups preferentially associated with particular other male subgroups. Females associated most consistently with other females, although not to the same extent as some males. Female associations were better described as a network rather than discrete subgroups. Male-female associations were generally inconsistent and depended in part on female reproductive state. Mothers and their offspring associated very consistently for at least 4 years.