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.