Why do swifts resemble swallows even though they are not closely related?

Swifts and swallows are not closely related, yet they share a striking resemblance in size, body proportions, and aerial habits. This similarity is a classic example of convergent evolution, a process where unrelated organisms independently evolve similar traits as a result of adapting to comparable ecological niches or environmental pressures.123

Because both groups are highly specialized for life on the wing—spending much of their time flying to capture insects—natural selection has favored similar physical adaptations in both. These shared traits include streamlined body shapes and long, efficient wings that facilitate agile, high-speed flight. While they may look alike to the casual observer, they belong to entirely different biological orders, and their anatomical structures reflect these distinct evolutionary paths.14