Buzz
The nests constructed by birds are as varied as the species themselves. From the sites they select to the forms, dimensions, and substances they employ, the diversity is truly remarkable. For instance, Hamerkops dedicate weeks to gathering thousands of twigs, creating a colossal nest that’s both insulated and waterproofed with mud. Similarly, the horned coot builds its nest atop a mound of pebbles it assembles in shallow waters. On the other hand, the edible-nest swiftlet constructs its dwelling entirely from solidified layers of its own saliva.
Even for someone like neurobiologist Zach Hall, who primarily studied avian brains during his doctoral research, the astonishing variety of nests was impossible to overlook. He also noted the lack of extensive research into how such diverse nest types evolved. Through a new study, Hall believes he has uncovered the evolutionary path of one type of nest—the protected dome-shaped structure. As the saying goes in real estate, location is everything, and dome nests seem to have emerged as certain birds shifted from tree-nesting to ground-nesting, requiring a nest design better suited to their new environment.
Hall acknowledges that this concept isn’t entirely novel. Nearly two decades ago, biologist Nicholas Collias proposed a similar theory to explain why some members of the Old World babblers family construct dome nests while others build open, cup-shaped ones. However, at the time, Collias lacked sufficient data and the necessary tools to validate his hypothesis. With a more comprehensive understanding of babblers’ evolutionary lineage and relationships now at hand, Hall and his team set out to determine if Collias’s idea still held merit.
The team collected data on the nests constructed by 155 distinct babbler species, documenting their heights and designs (either cup-shaped or dome-shaped), and linked these traits to the birds’ evolutionary tree. Their findings supported Collias’s theory. Within the babbler family, species that construct dome nests tend to live nearer to the ground compared to their cup-nesting counterparts. As these birds evolved from tree-dwelling ancestors that built cup-shaped nests, dome-shaped nests emerged alongside the shift to lower nesting sites.
Although they confirmed the correlation between nest height and structure, the researchers remain uncertain about which trait influenced the other. Nesting closer to the ground might have prompted some species to adopt dome-shaped nests for added protection against predators, as Collias proposed (though the team acknowledges other factors, such as parasites or the need for warmth in shaded forest areas, cannot yet be ruled out). Alternatively, the development of dome nests might have enabled these species to explore new nesting grounds. However, the team believes the former scenario is more plausible, as altering nest height is a simpler evolutionary step than changing nest shape, aligning with observations in other bird species.
While further research is needed, Hall’s team is optimistic that their methodology can resolve lingering questions about babblers and be applied to other bird species to uncover the evolutionary drivers behind their unique nesting behaviors.
