These bird nests show signs of an architectural “culture”

By Gennaro Tomma

Long and winding migratory flights complex songs and intelligent tool use, many bird behaviors are known to be socially transmitted and persist across generations – something scientists define as animal “culture”. A study now suggests that culture may also play a role in avian architecture.

Researchers analyzed more than 400 structures built by 43 different groups of White-browed Sparrows in the Kalahari Desert of southern Africa. These birds live communally and the entire cohort works together to build a nest and several perches from grass. The dominant female of the group then lays her eggs in the nest, which has a long, tube-shaped entrance. Individual birds sleep close together in the U-shaped roosts, which have both an entrance and an exit.

Scientists found that different gatherings of birds, even those living just a few meters from each other, built very different tubular structures. The biggest difference was “how long or short the structures were,” says the study’s lead author, Maria C. Tello-Ramos, a cognitive ecologist at the University of Hull in England. Tube width also varied between groups. Additionally, each group retained the same architectural style over time and when outsiders joined them, they adapted to that style.

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To examine why the groups built differently, the team analyzed factors that can determine the size and shape of a nest for a given bird species: weather conditions, tree height, body size of individuals and genetic relatedness. (If closely related birds build similar structures, for example, one might assume a genetic element.) Yet none of these factors appear to play a relevant role in how Kalahari sparrows build their nests, the researchers report.
In Science.

“Then we say, ‘Okay, so what’s left?’” Tello-Ramos says. She and her colleagues proposed that cultural transmission could be key to nest building. “In our paper, we haven’t gotten there yet with experiments, but we have very good indications that this might be the case,” she says.

“These are important questions that are understudied,” says Christina Riehl, an evolutionary biologist at Princeton University. She is not convinced that the study data is sufficient to completely rule out a genetic influence. “They can’t really look at the effect of, say, genetic differences, because they don’t have very good genetic information on all the individuals in these groups,” she says. “I think there’s a lot more to be done and I think this paper will inspire some really good future research.”