Dolphin girl gang uses sponges to catch prey and create a new culture

In brief: Female bottlenose dolphins in Australia use tools such as sponges for hunting fish. They teach their daughters this unique technique and create a new culture.

The presence of standard behavior is considered indicative of the culture. Scientists have long-questioned the existence of culture in non-human species. Culture is a reason for uniformity within groups and differences between groups. And this uniformity usually arises from social learning (observation and mimicking). In humans, culture is often different regionally or temporally. For example, London culture is different from the Los Angeles culture. Similarly, 1940s Los Angeles culture differs from the current Los Angeles culture.

Culture in non-human species has been cited in the great apes and some bird species. Then, recent studies have led to the question of culture in dolphins and other cetaceans.

Dolphin culture in Australia

In Shark Bay, Australia, a population of bottlenose dolphins (Tursiops truncatus) has been a case study for dolphin culture. This population includes over 500 bottlenose dolphins, and a subset of this population is foraging (feeding) in a novel way. They are using tools! Observation (social learning) is the primary transmitter of tool-use. Additionally, using tools is indicative of higher cognition or intelligence. Only 0.01% of non-primate mammals use tools. That makes tool-use staggeringly unique!

Dolphins use tools like sponges to catch prey

Interestingly, only around 50 of the Shark Bay dolphins use tools. This group uses cone-shaped sponges on their rostrum (or beak) to dig through the sandy bottom. The sponge protects their rostrums from scratches while forcing prey from the sand. As their prey attempts to escape, the sponge-wielding dolphins can then chase down their target. Dolphins hunt both visually and by producing clicking noises (echolocation) to pinpoint their prey. This specialized foraging activity has a name: sponging.

Dolphin girl gang creates this new culture

Two points make sponging unique.

• Historically, it is an entire population that uses a tool. In this case, only a small subset group is sponging.
• The “spongers” are almost all females. So, spongers have created an ocean girl gang.

Why is sponging performed predominately by females?

Learning to break off a piece of sponge and forage through the sand is a specialized behavior. Studies show sponging to be the result of vertical social learning (passed from mother to child). The higher proportion of female spongers is likely the result of the life history of dolphins. Female dolphins are mostly solitary. They rely on dependable food sources to provide for their calves. Bottlenose dolphin calves stay with their mothers for 3-8 years. Therefore, the presence of consistent sponge availability and plentiful seafloor prey make sponging a beneficial ecological trait.

The Shark Bay studies show that regular female bottlenose dolphins form open relationships with other females. However, sponging females display stronger associations with other spongers than with non-spongers. Therefore, creating the Sponging Clique.  

Males generalize while females specialize

Oppositely, males form strong life-long alliances with other males. They cannot restrict themselves to one foraging type. Males spend most of their life roaming large regions in search of mates. In other words, they can’t be tied down to the old ball-and-chain. Or, perhaps more accurately, the sponge-and-chain. The few sponging males are young adults. They are either still under the mother’s care or recently on their own. Occasionally, adult males sponge as well, but they do not specialize in it, thereby not constraining themselves to only one technique or location. To learn more about male bottlenose dolphin dynamics, click here.  

Inventive marine mammals

Tool-use is not uncommon in marine mammals. Sea otters use rocks to crack open shells while floating on their backs. Humpback whales use bubbles to trap prey, and orcas make waves to push seals off their ice floats. Yet, the unique aspect of the Shark Bay bottlenose dolphins is the subset of female spongers that have formed cliques. Is this an indication of a dolphin subculture and higher intelligence? A lack of scientific consensus on culture requires more discussion and research. What we do know is that there is a girl gang of sponging dolphins roaming Shark Bay, clicking and clique-ing together.

For further reading

• Krützen, et al. (2005) Cultural transmission of tool use in bottlenose dolphins. PNAS 102 (25): 8939-8943; doi: 10.1073/pnas.0500232102
• Mann J, Sargeant BL, Watson-Capps JJ, Gibson QA, Heithaus MR, et al. (2008) Why Do Dolphins Carry Sponges? PLoS ONE 3(12): e3868. doi:10.1371/ journal.pone.0003868
• Mann, J., Stanton, M., Patterson, E. et al. (2012) Social networks reveal cultural behaviour in tool-using dolphins. Nat Commun 3, 980. https://doi.org/10.1038/ncomms1983
• Whiten, Andrew. (2011) The scope of culture in chimpanzees, humans and ancestral apes. Phil. Trans. R. Soc. B366997–1007 http://doi.org/10.1098/rstb.2010.0334