Bird Nests: How Did They Evolve?

Bird nests, though it may not seem like it, are incredibly diverse, differing in nest location, structure, materials, and more. For instance, they could be on the ground or hanging from a tree, made out of twigs and grass, or even saliva. Yet despite their variety, we know very little about the forces that shaped their evolution. Now, new research is shedding light on the subject.

Specifically, researchers from the University of St. Andrews in Scotland are testing the hypothesis that domed-shaped nests arose as a result of some species transitioning to nesting on the ground, where the risk from predators is greater.

Surprisingly to scientists, previous research has rarely focused on why different bird species build such drastically different nest structures.

"I thought this was strange," researcher Zachary Hall said in a statement, "because the shape of a nest seems to be the most striking and diverse feature across bird species."

Although the idea that competition for nest sites, forcing some birds to the ground where predators were a threat, was first proposed nearly 20 years ago, techniques at the time did not provide a way to test the theory. But now, researchers are able to use more advanced statistical techniques to find the answer.

Hall and his colleagues collected previously published descriptions of the nests of 155 species of babbler and mapped nest height and structure to the birds' family tree.

Their analysis confirmed that babblers' ancestors likely built above-ground, cup-shaped nests, and that the addition of a dome to cover the nest corresponded with switching to nesting at ground level.

"This new study... looks at the evolution of two key aspects of animals as architects: how they shape their homes and where they put them," said Don Dearborn, an expert in the evolution of reproductive strategies in birds. "It shows very nicely how we can take advantage of recent progress in avian phylogenetics to test ideas about the evolutionary history behind the modern-day co-occurrence of particular pairs of traits."

The results were published in the journal The Auk: Ornithological Advances.

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