How do a swallow and a swift converge?

Such small and nimble birds as the swallow and the swift are very similar. Let’s list the similarities between the swallow and the swift: firstly, the diet of these birds is almost the same and it consists of flying insects, which they deftly grab in flight; secondly, these species of birds are migratory, that is, for the winter, swallows and swifts fly to the south, for wintering; thirdly, the shape of the body, head, and also the wings of these birds are very similar; fourthly, the swallow and the swift have a very similar forked tail.