Swifts

The Apodidae, or swifts, form a family of highly aerial birds. They are superficially similar to swallows but are not closely related to any passerine species. Swifts are placed in the order Apodiformes along with hummingbirds. The treeswifts are closely related to the true swifts but form a separate family, the Hemiprocnidae. Resemblances between swifts and swallows are due to convergent evolution, reflecting similar life styles based on catching insects in flight. The family name, Apodidae, is derived from the Greek ἄπους (ápous), meaning "footless", a reference to the small, weak legs of these most aerial of birds. The tradition of depicting swifts without feet continued into the Middle Ages, as seen in the heraldic martlet.