How did complex nest building help passeriforms spread into new habitats?

The complex nest-building behaviors of passeriform birds were a significant evolutionary development that helped them expand into diverse habitats. According to American ornithologist Nicola Collias, these advanced construction skills effectively released passerines from the constraints of being "obligatory cavity nesters," a limitation faced by their evolutionary predecessors.1

By gaining the ability to build nests in a wide variety of locations—such as in shrubs, trees, on ledges, or hanging from branches—passerines were no longer restricted to finding pre-existing holes or crevices in rocks and trees. This behavioral flexibility, combined with their superior neural capacities and a flexible body plan, allowed them to explore and successfully adapt to novel ecological zones. Consequently, passerines evolved to become the dominant group of modern birds, utilizing diverse materials like mud, spiderwebs, and plant fibers to create nests ranging from simple cups to elaborate, woven, or domed structures.21