Winter is coming. The possible return of our newest seasonal rock star, the polar vortex, means another season of sporadic bursts of frigid air and snow for much of the United States. It also means a return of the winter down jacket , which here in New England is a commodity just behind heating oil. It’s a clothing item most people take for granted because it gives us an impressive amount of warmth at a relatively reasonable price. But the cost is far greater for the birds whose feathers provide winter coats with their puffiness and cozy comforters with their fluffiness.