The Swifts are
a family, Apodidae, 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 with hummingbirds. The tree swifts 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,
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.