J A Leach on swallows:
The Australian members of the Swallow family present very different nesting habits. While the Welcome Swallow builds the well-known cup-like mud nest, the rare White-backed Swallow drills a two-inch hole into a bank for two or three feet, and there builds its nest. The Tree Martin (Swallow), on the other hand, makes no nest, but lays its eggs on leaves placed on the rotten wood in the hollow of a tree. The Fairy Martin builds a long, bottle-shaped mud flask, under a bridge, or a ledge, and so is sometimes called the Bottle or Retort Swallow. Wood-Swallows and Swifts do not belong to the Swallow family.
An Australian Bird Book, 1912, 2nd Ed. p102.
by J A Leach, M.Sc (1870-1929).