How did experiments with African long-tailed widowbirds test female preferences for long tails?

To test female preferences for tail length in the African long-tailed widowbird, researchers conducted experiments involving the artificial manipulation of male tail feathers.1

By artificially elongating the tails of male widowbirds, scientists were able to demonstrate that females exhibit a strong preference for males possessing the longest tails. This experimental evidence supports the runaway selection hypothesis, which suggests that such extreme physical traits evolve because females selectively mate with males displaying the most exaggerated versions of the preferred characteristic. Consequently, this process leads to the development of significant sexual dimorphism within the species.1