Dig this crazy architecture! Bank Swallows nest in cooperative apartments with sieve-like facades, excavated with beak and claw in the clay or sand of river banks, gravel pits, highway cuts and sawdust heaps. At the end of a 2- to 4-foot hallway, they place the family room, wall-to-walled with feathers and grass. Utilities? They eat, drink and bathe on the wing. But how do they know which hole to come home to?