Dolphins that hunt using sponges as tools prefer to spend time with other… (Eric M. Patterson )
Scientists have discovered that bottlenose dolphins have something in common with junior high school girls: They like to hang out in cliques. The researchers found that dolphins that wear sea sponges on their beaks as hunting tools prefer to hang out with other dolphins that do the same. The finding is the first strong example of cultural behavior in non-human animals.
While there is much disagreement among scholars over what constitutes a cultural behavior, there is broad agreement that it must include two central components: The behavior must be socially learned, meaning animals learn largely by observing and interacting with others, and it must also lead to identifiable groups, some of which exhibit the behavior and some of which don’t. In other words, it has to produce social cliques.
Dolphin experts already knew that the mothers taught their children how to hunt with sea sponges. But they had yet to show that sponge-hunters preferred the company of fellow sponge-hunters. Dolphins hunt alone, so researchers wanted to know whether the spongers spent more non-hunting time with other spongers than with non-spongers.
To answer this question, a team of researchers from Georgetown University used a social network analysis to examine a trait called “homophily,” or how likely dolphins were to associate with other dolphins who hunted the way they did. The analysis was complicated by the fact that dolphins, like humans, associate with a wide range of other dolphins, but for varying amounts of time. As a result, the analysis required a significant amount of data.
In the report, published Tuesday in the journal Nature Communications, the researchers analyzed 22 years of records recounting the observed interactions between 36 sponge-hunters and 69 non-spongers.
They found that female spongers—but not males—spent more time with fellow sponge-hunters than with non-sponge-hunters. While the researchers were unsure why they found this sex difference, they suspect it is related to the different approaches male and females dolphins take to social behavior in general.
The researchers do not claim that hunting techniques are the primary determinant of dolphin social behavior. More important in determining associations, they write, may be “enduring traits such as sex, kinship, age, and geography,” traits that are often definitive in human culture as well. Nevertheless, the scientists say that their results demonstrate that socially learned behaviors do play a role, just as they do in pre-teens. As a result, they believe that there are likely to discover more examples of animal cultural behaviors in the future—sponging may be just the tip of the iceberg.
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