A tide is turning for the swallows

Wenlock Edge What determines that moment when they can stay no longer, when, come hell or high water, it’s time to go? Like clothes pegs on a washing line the swallows are still, perching on the electricity cables. For once, since they arrived in spring, they have to stop, even in daylight. What they are pegging on the line between them is an invisible sheet, a map of their endless journey, north and south.They pause. Seconds ago they were skimming at breakneck speed inches above the grass