How do large brains and behavioral flexibility help passeriform birds adapt?

The evolutionary success of passeriform birds is attributed to a combination of factors rather than a single trait. According to ornithologists, the combination of large brain size and behavioral plasticity—along with rapid population turnover—has allowed these birds to adapt more effectively than nonpasserines.1

Specifically, these neural capacities and a flexible body plan enabled passeriforms to explore and successfully colonize novel environments. This adaptability was further enhanced by complex nest-building behaviors, which freed these birds from the constraints of the obligatory cavity-nesting habits seen in their predecessors, facilitating their expansion into new ecological zones and habitats. Together, these traits have likely accelerated the rates of morphological evolution and speciation within the order.1