3000 m (high)
(9840 ft)
animaldiversity.ummz.umich.edu
Barn swallows are very adaptable birds and can nest anywhere with open areas for foraging, a water source, and a sheltered ledge. They seek out open habitats of all types, including agricultural areas, and are commonly found in barns or other outbuildings. They will also build nests under bridges, the eaves of old houses, and boat docks, as well as in rock caves and even on slow-moving trains.
Physical Description
Barn swallows are small birds. They range in size from 14.6 to 19.9 cm long, with a wingspan of 31.8 to 34.3 cm. They weigh between 17 and 20 g. Barn swallows are metallic blue-black above and pale beige below. They have light brown on their throat and forehead, and have a long, deeply-forked tail. Males and females are similar in appearance, though females tend to be less vibrantly colored and have shorter outer tail-streamers.
Asymmetry of physical characteristics in barn swallows tends to be transmitted to the young in distinct parent to offspring patterns. Tail asymmetry tends to pass from father to son and from mother to daughter. Alternatively, wing asymmetry does not appear to transfer at all on a reliable basis from parent to offspring.
Reproduction
Barn swallows are socially monogamous. However, extra-pair copulations are common, making this species genetically polygamous. Breeding pairs form each spring after arrival on the breeding grounds. Pairs re-form each spring, though pairs that have nested together successfully may mate together for several years. Males try to attract females by spreading their tails to display them and singing.
Several studies have researched sexual selection in barn swallows. Moller (1994) documented female barn swallows selecting for symmetrical wings and tails in potential mates. Males exhibiting greater symmetry acquired mates more quickly than did asymmetric males. Asymmetry can result from genetic factors such as inbreeding or mutations as well as from environmental stress such as food deficiency, parasite infestation, or the presence of pathogens. Moller observed that individuals affected by these factors not only exhibited asymmetry, but also decreased strength and longevity. Therefor, females that selected symmetrical mates would presumably be selecting superior mates. In addition to selecting for symmetry, females also tend to select males with longer tail feathers. Moller observed a connection between the tail length of male barn swallows and their offspring’s vitality and longevity. Males with longer tail feathers exhibit traits of greater longevity which is passed on to their offspring. Females thus gain an indirect fitness benefit from this form of selection, as longer tail feathers indicate a genetically stronger individual who will produce offspring with enhanced vitality. Individuals with longer tails have also been observed to demonstrate greater disease resistance than their short-tailed counterparts. There is also evidence that males select female mates with long tails.
Unmated adults often associate with a breeding pair for up to an entire season. Though these “helpers” do not usually feed the young, they may help with nest defense, nest building, incubation and brooding. “Helpers” are predominantly male, and may succeed in mating with the resident female, leading to polygyny. (Bolzern, Moller, and Saino, 1997; Brown and Brown, 1999; De Lope and Moller, 1993; Moller, 1993; Moller, 1994a; Moller, 1994b)
Barn swallows usually breed between May and August, but this varies greatly with location. They usually raise two broods of chicks each summer. Both birds of a pair make the nest. They build the shell of mud, and line it with grass and feathers. The female lays 3 to 7 eggs (average 5). Both parents incubate the eggs, which hatch in 13 to 15 days. The chicks are naked and helpless when they hatch. Both parents feed and protect the chicks, as well as removing fecal sacs from the nest. The nestlings remain in the nest for about 20 days before fledging. When barn swallows are handled by humans they tend to attempt to fledge at least a day too early. The parents continue to care for the chicks for up to a week after fledging, feeding them and leading them back to the nest to sleep. By two weeks after fledging, the barn swallow chicks have dispersed and often travel widely to other barn swallow colonies. Young barn swallows are able to breed in the first breeding season after they have hatched. Generally, young barn swallows do not produce as many eggs as do older birds. (Brown and Brown, 1999; McWilliams, 2000; Perrins, 1989; Terres, 1980)
