A Major Discovery in Bird Architecture: How Predators and Climate Shape Different Nest Designs
Bird nests are not only places where birds raise their young but also sophisticated structures shaped by millions of years of evolution. Yet scientists have long debated why some species build enclosed nests. Why do some birds invest extra effort in constructing roofed nests or breeding in tree cavities and burrows instead of using more common open cup nests? Are these designs primarily adaptations against predators or harsh climates?
An international research team from the Biodiversity Research Center of Academia Sinica and the University of Maryland addressed this question by combining large open datasets on bird distributions, environmental conditions, predator distributions, and species traits. Using phylogenetic regression models, they analyzed data from more than 7,400 bird species worldwide (about 74% of all known bird species). This is the first global-scale study to systematically identify the ecological factors driving the evolution of different nest types.
The study found that the two main forms of enclosed nests, domed nests and cavity nests, serve fundamentally different functions. In passerine birds, domed nests primarily reduce predation risk. Birds are more likely to build domed nests in regions with greater predator diversity, especially species at high risk of predation, such as ground nesters, non-cooperative breeders, and species with larger clutches. The roof likely helps conceal the nest and hinder predator access.
By contrast, cavity nests in tree holes and burrows appear to be adaptations to challenging climatic conditions. Cavity nesting is more common in dry regions, areas with large temperature fluctuations, and generally extreme climates. Tree trunks and soil provide insulation that buffers temperature changes and creates a more stable microclimate for eggs and nestlings. This advantage is particularly important for small species with small eggs and limited thermoregulatory capacity.
Beyond resolving a long-standing question in evolutionary biology, the study provides new insights into the evolution of global biodiversity and practical guidance for conservation. According to the corresponding authors, Stephanie Chia and Mao-Ning Tuanmu, understanding the ecological functions of nests is becoming increasingly important as climate change intensifies.
For example, artificial nest boxes can help many bird species reproduce, but they often provide less insulation than natural tree cavities. For species at risk from extreme temperatures, nest-box design should therefore consider thermal insulation to avoid creating “ecological traps.” Climate change may also alter predator activity patterns, potentially increasing predation pressure on exposed open nests.
These findings remind us that conservation planning, habitat restoration, and artificial nest-box design should all take into account the important ecological functions of these seemingly simple but highly sophisticated natural structures.
This research was supported by the Academia Sinica Career Development Award and the U.S. National Science Foundation. The study was published in June 2026 in the journal Global Ecology and Biogeography.
Article link: http://dx.doi.org/10.1111/geb.70265
