Why do some birds build nests so thin you can see the egg underneath?

Nature · Published 3 October 2026 Swipe more like this →

In short: The Cotingidae family is a masterclass in evolutionary diversity. While some of these tropical birds share parenting duties, others rely on elaborate, high-stakes courtship displays. From mud nests on cliff faces to nearly transparent platforms, their nesting habits are as varied as their striking plumage and far-carrying calls.

The Cotingidae family, formally introduced in 1849 by Charles Lucien Bonaparte, encompasses 66 distinct species across 24 genera. These suboscine passerines are primarily found throughout the tropical forests of South and Central America. While they share physical traits like powerful legs, rounded wings, and broad, hooked bills, their social structures are remarkably polarized. Roughly half of the species engage in biparental care, while the other half leaves all child-rearing responsibilities to the female.

This divide dictates the birds' behavior and appearance. In species where females raise offspring alone, males often congregate in leks—communal display grounds—to compete for mates. This sexual selection has driven the evolution of extravagant features, such as the umbrella-like crests and throat wattles of the Amazonian umbrellabird, or the vibrant colors of the Guianan cock-of-the-rock. In contrast, species that share parenting duties tend to exhibit less dramatic differences between the sexes, with females generally appearing duller than males across the entire family.

Nesting strategies within the family are equally diverse. Some species construct remarkably flimsy, platform-like nests that leave a single egg visible from below, a potential adaptation to evade predators. Others, like the cock-of-the-rock, utilize mud to anchor their nests to cliff sides, while fruiteaters construct more conventional, solid cup nests. Regardless of the method, these birds face significant conservation challenges, as their habitats—ranging from coastal mangroves to humid tropical forests—are increasingly threatened by environmental loss.

Recent scientific inquiry has refined our understanding of their lineage. A 2014 study by Jacob Berv and Richard Prum identified five distinct monophyletic clades within the family, a structure further supported by 2020 research. This ongoing taxonomic work, including the reclassification of certain genera into the Tityridae family, highlights the complex evolutionary history of these birds. As researchers continue to map their phylogeny, the Cotingidae remain a vital subject for understanding how climate and social behavior shape avian evolution.

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