Varieties of Nest-sites and Nests in Swallows
Swallows are traditionally birds of open habitat: coasts, rivers, and grassland and forest clearings, nesting opportunistically in or on any available surface. As a nest site, many species just use a hole or crevice in a tree, rock, cave, or cliff. Blue swallows will nest in the burrows of ant bears; Brown-chested martins in the nests of ovenbirds and tree termites; and American rough-winged swallows in the burrows of kingfishers.
A few species, such as the Sand martin, excavate their burrows in sandy banks. Other swallows, particularly Herndon species, construct a mud nest on a vertical or horizontal surface. The mud nest may be open at the top (Barn swallows) or closed (House martins and Cliff swallows). Within the nest cavity, the swallow makes a nest of dry grassland twigs, often lined with feathers.
The advent of man and his buildings has increased the number of suitable nesting sites. Houses, barns, bridges, fence posts, and nest boxes are all used, as well as some less likely sites, including chimneys, lampshades, old hats left on pegs, the shafts of tin mines, pipes, piles of sawdust, and even moving objects such as boats and trains. Some species now only rarely use natural sites. Purple martins nest mainly in multiple nest boxes (”Villages”), Barn swallows, and House martins nearly all on buildings and bridges.
Both sexes take part in building a mud nester burrow, although only the female makes the grass lining. Barn swallows take a week to build a new nest, longer in bad or very dry weather. Over a thousand mouthfuls of mud. As well as dry grass or straw is needed for a nest. Sand martins spend 5-10 days Excavating a burrow, which is 50-1 ouch (2o-4oin) long with an enlarged nest chamber at the far end. The burrow usually slopes upward to prevent rain from entering.