Dolphins Labeled as Workaholics
Georgetown Researcher is First to Examine the Relationship between Tool Use and Fitness in Wild Animals
December 10, 2008 – A new study that examines a subset of Western Australia’s Indian Ocean bottlenose dolphin population and its use of marine sponges as tools, provides an opportunity to assess costs and benefits of tool use while documenting patterns of transmission from mother to calf.
The study, led by Georgetown professor of biology and psychology Janet Mann, examines the relationship between tool use and fitness in wild animals. The researchers' findings are published in the Dec. 10 edition of the journal PLoS ONE.
While rare in wild animals, tool use is of widespread interest to researchers because of its relationship to animal cognition, social learning and culture. Yet measuring the costs and benefits of tool use has been difficult -- largely because if tool use occurs, all population members typically exhibit the behavior.
“It turns out the brainiacs of the marine world can also be tool-using workaholics, spending more time hunting with tools than any nonhuman animal,” says Mann, who has been studying the Shark Bay dolphin population for more than 21 years. “This is the first and only clear case of tool-use in a wild dolphin or whale.”
Mann, who started systematic data collection on the sponging behavior in these dolphins in 1989, found that 41 dolphins, in a population of thousands, use marine sponges on their beaks as a foraging tool. These dolphins use sponges to find hidden prey in the sandy sea floor and spend more time using their sponge-tool than any nonhuman tool user documented to date. Spongers are also “workaholics” spending more time hunting and diving -- for longer time periods, than other female dolphins in the population. They also tend to be solitary.
Comparing sponge-carrying female dolphins to nonsponge-carrying dolphins, the researchers observed that spongers were more solitary, spent more time in deep water channel habitats, dived for longer durations and devoted more time to foraging than nonspongers. They also found that even with these potential immediate costs, such as less time socializing, calving success of sponger females was not significantly different from nonspongers.
“Despite these costs, they are successful at calving, so their workaholic tendencies pay off,” says Mann.
Mann and her co-authors also report a clear female-bias in the development of sponging. Almost all the spongers are female, and they transmit this behavior to their offspring.
“While a few males carry sponges, they seem to be slow learners in this regard,” notes Mann. Her team found that all female calves started sponging before they were weaned, whereas male calves rarely used sponges, and if they did, it was after weaning.
While Mann continues to seek answers to new questions in her research on animal behavior, she also works with her students on their own research questions, both on the Shark Bay project and in the classroom.
Her students are examining the long-term development and transmission of foraging behavior, social networks and factors related to female reproductive success. Mann teaches courses on animal behavior and monkeys, apes and humans at Georgetown. She also takes up to four students with her to Australia each summer to give them the opportunity to learn the latest field research techniques.
Additional researchers on Mann’s team were from Florida International University in Miami, Metropolitan State College of Denver and University of Massachusetts at Dartmouth.
The study was funded primarily by the National Science Foundation with additional support from the Eppley Foundation for Research, the Helen Brach Foundation, the National Geographic Society’s Committee for Research and Exploration and Georgetown.