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The barn swallow will mob intruders such as cats or accipiters that venture too close to their nest, often flying very close to the threat. [60] Adult barn swallows have few predators, but some are taken by accipiters, falcons, and owls. Brood parasitism by cowbirds in North America or cuckoos in Eurasia is rare. [6] [37]
The typical nest is a grass or feather-lined deep closed mud bowl with a small opening at the top, [12] but many Asian house martins leave the top of the nest open. [ 20 ] [ 21 ] [ 22 ] David Winkler and Frederick Sheldon believe that evolutionary development in the mud-building swallows, and individual species follow this order of construction.
They have a slender streamlined body, long pointed wings and a short bill with a wide gape. The feet are adapted to perching rather than walking, and the front toes are partially joined at the base. Eight species have been recorded in Michigan. Cliff swallow, Petrochelidon pyrrhonota; Bank swallow, Riparia riparia; Barn swallow, Hirundo rustica
The Eurasian crag martin builds a nest adherent to the rock under a cliff overhang or increasingly onto a man-made structure. It makes a neat half-cup mud nest with an inner soft lining of feathers and dry grass. Nests are often solitary, although a few pairs may breed relatively close together at good locations.
It is much more urban than the barn swallow, and will nest even in city centres if the air is clean enough. [14] It is more likely to be found near trees than other Eurasian swallows, since they provide insect food and also roosting sites. This species does not normally use the reed-bed roosts favoured by migrating barn swallows. [16] [17]
Mud-nesting species in particular are limited in areas of high humidity, which causes the mud nests to crumble. Many cave-, bank-, and cliff-dwelling species of swallows nest in large colonies. Mud nests are constructed by both males and females, and amongst the tunnel diggers, the excavation duties are shared, as well.
The nest, built by both adults over several weeks, is made from several hundred mud pellets and lined with feathers and soft, dry grass, hair, sheep's wool or plant down. [27] It may be a half-cup when constructed under an overhang on a vertical wall or cliff, or shaped as a bowl like that of the barn swallow when placed on a sheltered ledge.
The genus Ptyonoprogne is closely related to the larger swallow genus Hirundo into which it is often subsumed, but a DNA analysis showed that a coherent enlarged genus Hirundo should contain all the mud-builder genera. Although the nests of the Ptyonoprogne crag martins resembles those of typical Hirundo species like the barn swallow, the DNA ...