The nesting habits of Cliff Swallows are fairly unusual in that these swallows are colonial nesters. Here in the East you can find 20 or 30 of their nests under a bridge or the eaves of a barn (and occasionally on cliffs). In the West, colonies consist of up to 3,500 nests! The construction of their gourd-shaped nest requires between 900 and 1,200 trips to mud puddles or stream banks, where they gather a mouthful of mud in the form of a pellet. Often two swallows will build nests side-by-side, sharing the wall of mud that separates them. Unfortunately, according to the most recent Vermont Breeding Bird Atlas, the Cliff Swallow population in Vermont has declined by 48% in the past 25 years, a fact which is attributed to competition with House Sparrows, a decline in insects due to diminishing farm land, and destruction of nests by humans. These birds are more important insect predators than ever, with the bat population having suffered such a decline recently due to white-nose syndrome.