Trading Wakes

Describe for me a sweeping arc
Inscribed upon the sky
By graceful torsion of swift wings,
The swallows’ keen and cry.
Pale filaments of latticed cloud
Distorted by the shear,
Gossamer threads, now severed
By the martins, as they veer
To trade their wakes by fading light,
An asymptote approaching,
But peel away to rafters, home—
An axis, now encroaching.