The Common Swift

Consider in its turn the common swift.

There is new evidence that over the dark dunes

of the Sahara, a swift will stay aloft two hundred days.

Scientists are puzzled, not over how,

but why. Consider the work, they note,

of sleeping in flight: the alertness demanded,

the tacks and turns it takes to ride the wind.

Even a gliding bird would expend

a small but constant effort. For such a cost,

there must be benefit. That is the equation

of science, a half a turn

from love. Consider in its turn

a marriage, surely no less common

or marvellous than swifts.

Surely no less a nest built in the air.