Evolution of enclosed nests in birds driven by predation and climate challenges

Nest structure plays a critical role in the reproductive success of birds, varying widely across species and environments. However, the evolutionary drivers behind enclosed nests remain unclear, with previous studies yielding inconsistent results. Using a global dataset including over 7,400 bird species, this study tests two key hypotheses—protection from predation and microclimate regulation—as drivers for the evolution of enclosed nests. Our results show stronger overall support for the predation hypothesis, but nest functions can vary by type. Dome nests are primarily used by passerines, especially ground-nesters, to mitigate predation risks, whereas cavity nests offer better microclimate regulation in arid or cold environments across both passerine and non-passerine species. These findings resolve long-standing debates on the functions of enclosed nests, reveal potential evolutionary mechanisms behind nest adaptations, and offer valuable insights into how bird species may respond to future environmental challenges.