Fashion-conscious bowerbirds may be the latest animals to show off a bit of culture. Differences in bower decoration within a single population of spotted bowerbirds come about because of local traditions, a new study finds, demonstrating a type of social learning rarely seen outside of primates.
Male bowerbirds build bowers--twig tunnels furnished with decorations--that are designed to entice females and act as a stage for courtship and copulation. The better built the bower and the fancier its embellishments, the more alluring it is to females and the more mates its male architect can attract. Building plans vary according to species, and they sometimes depend on the availability of decorating materials. Now, a study hints at an additional factor: local building traditions.
Joah Madden of the University of Cambridge, U.K., and his colleagues examined bowers built by the spotted bowerbird, Chlamydera maculatain Taunton National Park in Queensland, Australia, and found local preferences for particular bower ornaments. In the west of the park, for example, all bowers contained blue or purple glass, whereas this decoration was nowhere to be seen on bowers in the east. The team says this is evidence of local traditions, with males adapting their bowers to suit local tastes.
Madden says his team can rule out several competing explanations. First, DNA analysis suggests that related males (which might have similar tastes due to genetic similarity rather than learning) aren't grouped together. Second, the vegetation surrounding a bower and hence the light conditions do not appear to influence which objects males choose. And, crucially, there is no relationship between the local availability of objects and what ends up on a bower, so similarities between neighboring bowers are unlikely to come about simply because some objects are just easy to find, the team reports in a paper now in press at Animal Behaviour.
The study shows that bowerbirds have an esthetic sense, says Frans de Waal, a psychologist at Emory University in Atlanta. There is no reason why cultural traditions should be the preserve of primates, he says. "We just have totally underestimated how widespread social learning is in animals." It remains to be seen, however, whether the bowerbird traditions exist because males are copying the decoration selection made by their more successful neighbors or whether the preferences of females dictate the males' choices of ornamentation.