Amidst mewing barnyard cats and the mild scent of cow dung, a tricky game is in progress among the local swallows – find a partner!
The swallows fly past each other. Males and females can be distinguished by the length of their tail feathers. Those of the males are longer.
The males spread out their tail feathers, and the females inspect them. Most attractive is a male with long tail feathers. The females tend to follow him.
Birds are constantly plagued with parasites, but a male with a long tail usually has very few. By choosing such a male, the female reduces the risk that she, her nest or her offspring will be exposed to parasites.