sentences:  As one of the earlier migrants, this conspicuous species is also seen as an early sign of summer's approach.In the Old World, the barn swallow appears to have used man-made structures and bridges since time immemorial.An early reference is in Virgil's "Georgics" (29 BC), ""Ante garrula quam tignis nidum suspendat hirundo"" (Before the twittering swallow hangs its nest from the rafters).