Hili’s predecessor, the wise but now-deceased tabby cat Pia, used to annoy Andrzej by sticking her whiskers in his ears when he was sleeping. We’ve now discovered that chimps show a related behavior: sticking grass stems in their ears for no good reason.
A new paper in Animal Cognition by Edwin van Leeuwen et al. documents this finding, although its significance is, to me at least, unclear. We already knew that chimps show social imitation of behaviors, like fishing termites from their mounds using a masticated grass stem, or making sponges out of chewed-up leaves to soak up water to drink. The new result here is social learning of a behavior with no clear adaptive significance.
van Leeuwen report this social learning in a captive colony of orphaned chimps in Zambia. In one colony, a chimp named Julie began sticking pieces of grass in her ears for no apparent reason, and then engaging in her normal activities with the grass hanging out of her head. From the paper:
“Grass-in-ear behaviour” (henceforth “GIEB”) was first documented in 2010 when the first author observed one female chimpanzee (Julie) repeatedly putting a stiff, straw-like blade of grass in one or both of her ears. She left the grass hanging out of her ear(s) during subsequent behaviour such as grooming, playing, and resting (Figs. 1, 2 and Online Resource 1); the behaviour served no discernible purpose.
Here are some photos and captions from the paper:
Besides this behavior having no known function, it is clearly passed on socially, beginning with one chimp and then spreading to eight of the twelve others in the troop (two of these did it only once). The authors conclude that, because the behavior wasn’t seen in three of the other four isolated troops in the same area (well, it was one time), “ecological factors were not determiners of the prevalence of this behavior.” Well, that’s true, though perhaps the behavior might have had some connection with ecology (parasite removal?). But I highly doubt that.
The behavior is simply an example, I think, of chimps showing social learning of stupid things. It reminds me of my own youthful behavior when I learned to stick a pair of long soda straws up my nostrils and walk around saying, “Look—I’m a walrus!” Perhaps there’s a decorative element here, and chimps feel that grass hanging out of their ears makes them feel and look attractive, but that’s a stretch. It seems to be simply a spandrel of the social learning that we already know exists in this species.
The authors’ conclusion doesn’t say much, but hey, it’s something you can publish, and is a new result:
Regardless of the precise mechanism underlying the behavioural diffusion, our observations importantly show that chimpanzees spontaneously copy arbitrary behaviour from their group members. In line with Hobaiter and Byrne (2010), we interpret our data as reflecting chimpanzees’ proclivity to actively investigate and learn from group members’ behaviours in order to obtain biologically relevant information. The fact that these behaviours can be arbitrary and outlast the originator speaks to the cultural potential of chimpanzees.
van Leeuwen, E. C., K. Cronin, et al. (2014). “A group-specific arbitrary tradition in chimpanzees (Pan troglodytes).” Animal Cognition DO – 10.1007/s10071-014-0766-8: 1-5 LA – English.