"s nest in obscure places, in dark and cramped spaces: hollows beneath roof tiles, behind the intakes for ventilation shafts, in the towers of churches. To reach them, they fly straight at the entrance holes and enter seemingly at full tilt. Their nests are made of things snatched from the air: strands of dried grass pulled aloft by s; molted pigeon-breast feathers; flower petals, leaves, scraps of paper, even butterflies. During World War II, swifts in Denmark and Italy grabbed , reflective scraps of tinfoil dropped from aircraft to confuse enemy radar, flashing and twirling as it fell. They mate on the wing. And while young martins and s return to their nests after their first flights, young swifts do not. As soon as they tip themselves free of the nest hole, they start flying, and they will not stop flying for two or three years, bathing in rain, feeding on airborne insects, winnowing fast and low to scoop fat mouthfuls of water from lakes and rivers."