For instance, it has been observed in Great Britain that migrating swallows arrive earlier in the spring than swifts, this correlates with the later profusion of small insects that swifts feed on. Weather also affects the availability of flying insects.
This phenomenon can be illustrated by noting that migratory swallows typically arrive at their breeding grounds before swifts do in Great Britain, which is linked to the later abundance of small insects that swifts rely on for sustenance. Weather conditions also influence the population dynamics of flying insects.