The Shark Bay Dolphin Research Project is the second longest running dolphin field study worldwide (located in Western Australia, see www.monkeymiadolphins.org) and involves over a dozen investigators from three continents. This resident population of dolphins live in clear, shallow, protected waters, permitting detailed observations. Records on the dolphins go back to 1982 and are nearly continuous since 1984. The long-term data are managed at Georgetown with the help of graduate students, a research associate, and particularly Lisa Singh, in Computer Science, who, with her students is helping us build a data warehouse. Our goal is to build an integrated relational database for processing and analyzing information on the dolphins, including demographic, reproductive, genetic, ecological, behavioral and acoustic data.
My own research in Shark Bay began with a longitudinal study, the Dolphin Mother-Infant Behavioral Ecology Project, initiated in 1988. We’ve studied over 115 calves born to 71 mothers and are examining a number of problems concerning calf development, female reproduction, genetics, ecology and behavior. I am generally interested in why bottlenose dolphins have such slow life histories, why females invest substantially in each calf, and what factors predict female reproductive success. These questions have both theoretical and applied (conservation and management) value.
Much of my work is collaborative, with graduate students taking the lead on a number of topics. Jana Watson-Capps (PhD 2005) and I published a paper on the causes of calf mortality, testing whether predation risk or calf condition are the primary causes. We don't tag or capture dolphins in
Weaning age in
One of the great pleasures in behavioral research is observing individual differences in and how calves change as they grow up. Quincy Gibson (PhD 2007) and I have two papers coming out this year (Gibson & Mann in press a,b) pertaining to individual differences in calves and how-when sex-specific strategies emerge. Calves form distinct social patterns while still dependent on their mothers. This is evident during temporary mother-calf separations, where the calf typically joins others or forages alone. When mother and calf are together, they associate primariliy with females and male calves, but avoid juvenile and adult males. During separations, calves of both sexes preferentially associated with immatures over adults, but male calves also preferred juvenile and adult males. The sociability of the mother also influenced calves; daughters mirrored their mothers during separations, whereas sons did the opposite, seeking more social contact if their mothers were solitary and less social contact if their mothers were sociable. These sex-specific patterns foreshadow strategies that are likely to be successful for males (alliance formation) and females (adoption of maternal social patterns) in the future.
Few behaviors are more thrilling to watch than calf play. Dolphins are known for their playfulness, yet we understand little about the meaning and function of play. Most theories of play suggest that it strengthens behavior patterns and social skills that young animals will need later in life, but it may also help foment bonds that are important when they are young. I recently examined patterns of sociosexual behavior during development published in Homosexuality in Animals (Mann 2006). Sociosexual play usually involves mounting, goosing (beak to genital contact) and other types of close physical contact. Male calves engage in sociosexual play at much higher rates than female calves, similar to patterns found in other mammals. However, unlike other mammals, sociosexual play often involves multiple partners simultaneously and synchronous behavior, such as two young males simultaneously attempting to mount a male or female. Males often exchange roles (actor and recipient) with each other. Overall, the patterns of sociosexual behavior suggest that males and females are practicing for adult courtship behavior and that males begin to develop close bonds during this period. This might be expected given the importance of male alliances in adulthood.
Social experience is obviously important, but before a calf can be weaned, s/he must learn to hunt for themselves. This is no easy task. Calves begin foraging in the first year, but must sometimes develop highly specialized skills for finding, capturing and processing prey. In collaboration with Brooke Sargeant (PhD 2005), we have been investigating the development of calf foraging tactics and whether these are primarily socially learned from the mother or other individuals. More than 13 foraging types have been identified and each adult female has a distinct foraging profile. For example, we are looking at the development of tool-use (sponge-carrying, described in the foraging section) in a subset of our population. We have observed approximately 14 sponge-carriers and their offspring. Most of the calves appear to adopt the sponge-carrying technique, although the behavior shows a distinct female bias (Mann & Sargeant 2003). Vertical social transmission is strongly implicated in the development of most foraging tactics. If social influence is a factor, some foraging behaviors might be considered traditions or cultures. This naturally depends on one’s definition of tradition or culture. Analysis of mitochondrial DNA haplotypes suggest that this tradition is spread exclusively through matrilines (Krützen et al. 2005). We have also found that social factors and habitat are important predictors of many, but not all foraging behaviors (Sargeant et al. 2005; Sargeant et al. 2007; Sargeant & Mann 2007; Mann et al. 2007). We are currently extending this work and examining the mechanisms of transmission and long-term impacts of foraging behavior on survival and reproduction.
(at top left) Aerial view of the study area, Monkey Mia, Shark Bay in Western Australia.
(at middle right) Calf "Peglet" nursing in Shark Bay
(bottom right) Juvenile female "Demi" carrying a sponge. Some bottlenose dolphin females in Shark Bay use sponges as a foraging technique to probe the bottom. Demi carried a sponge as a calf. Her mother, "Half-fluke" was also a sponger. This is one potential example of cultural traditions in dolphins and is the only documented case of tool-use in wild cetaceans.