Swallows

Identification

Eight members of the swallow family Hirundinidae breed in North America: the tree swallow (Tachycineta bicolor), violet-green swallow (Tachycineta thalassina), purple martin (Progne subis), bank swallow (Riparia riparia), northern rough-winged swallow (Stelgidopteryx serripennis), barn swal-low (Hirundo rustica), cave swallow (Hirundo fulva), and the cliff swallow (Hirundo pyrrhonota). Of the eight spe-cies, barn and cliff swallows regularly build mud nests attached to buildings and other structures, a habit that sometimes puts them into conflict with humans. This is particularly true of the cliff swallow, which nests in large colonies of up to several hundred pairs. Barn swallows tend to nest as single pairs or occasionally in loose colonies of a few pairs. Some homeowners consider barn swallows to be at most a minor nuisance. Many homeowners tolerate nesting barn swallows as pleasant and interesting summer companions around the home. This chapter will focus on cliff and barn swallows because of their close association with humans.

The cliff swallow, 5 to 6 inches (13 to 15 cm) in length, is the only square-tailed swallow in most of North America. It is recognized by a pale, orange-brown rump, white fore-head, dark, rust-colored throat, and steel-blue crown and back.

The barn swallow, 5 3/4 to 7 3/4 inches (15 to 20 cm) in length, is the only swallow in the United States with a long, deeply forked tail (Fig. 2). Barn swallows have steel-blue plumage on the crown, wings, back, and tail. The forehead, throat, breast, and abdomen are rust colored. Females are usually duller colored than the males. 

General Biology, Reproduction, and Behavior

Migration

Cliff and barn swallows winter in South America. They begin a north-ward migration in late winter and early spring overland through Central America and Mexico. Swallows migrate during the day and catch flying insects along the way. They will not penetrate regions unless flying insects are available for food, which occurs after a few days of relatively warm weather, 60 to 70 o F (16 to 21 o C) or more. Arrival dates can vary greatly with weather conditions. In general, cliff and barn swallows enter the southern United States in mid-March to mid-April and reach the northern portions of their range by early June. Site Selection Swallows have a homing tendency toward previous nesting sites. Under suitable conditions, a nest is quite durable and may be used in successive years. Most cliff swallows arrive at a particular colony within a 24-hour period. At large colonies, swallows may arrive in successive waves. Resident adults are the first to return, followed by adults who bred at other colonies, and by young swallows who have not yet bred. The younger swallows include individuals not born at the selected colony. Swallow nests are inhabited by hematophagous (bloodsucking) insects and mites. Swallow bugs (Oeciacus vicarius), most common in cliff swallow nests, can spread rapidly by crawling from nest to nest in a new colony or by clinging to the feathers of adults. Infestations of swallow bugs and mites reduce nestling growth rates and cause up to half of all nestling deaths. Swallow bugs are able to survive  in unoccupied nests for up to 3 years without feeding and await returning swallows in spring. In selecting a nest site, cliff and barn swallows apparently assess which nests are heavily infested with parasites and avoid them. Cliff swallow colonies often are not reoccupied after 1 or 2 years of use because of heavy infestations. Cliff swallows will even prematurely desert their nests en masse, leaving their young to starve, when swallow bug populations become too great.

Nest Construction

Cliff swallow nests are gourd-shaped, enclosed structures with an entrance tunnel that opens downward (Fig. 1). The tunnel may be absent from some nests. The mud pellets used to build the nest consist of sand and smaller  amounts of silt and clay. The nest chamber is lined sparingly with grasses, hair, and feathers. The nest is cemented with mud under the eave or overhang of a building, bridge, or other vertical surface. The first cliff swallow nests on structures are usually located at the highest point possible, with subsequent nests attached below it, forming a dense cluster. Barn swallow nests are cup-shaped rather than gourd-shaped, and the mud pellets contain coarse organic matter such as grass stems, horse hairs, and feathers . The nest cup is profusely lined with grasses and feathers, especially white feathers.

Barn swallow nests are also typically built under eaves or similarly protected sites but not necessarily at the highest point possible. Barn swallows often use a beam or the protruding edge of a door or window jamb as the base for the nest, or attach the nest at the juncture of the two walls of an interior corner. Both male and female cliff and barn swallows construct the nest, proceeding slowly to allow the mud to dry and harden. Depending on mud supply and weather, nest construction may take 1 to 2 weeks. Mud is collected at ponds, puddles, ditches, and other sites up to 1/2 mile (0.8 km) away, with many swallows using the same mud source. A typical cliff swallow nest contains 900 to 1400 pellets, each representing one trip to and from the nest.

Did you Know

Food left out for household pets is often equally attractive to some wildlife species. In these situations, the wildlife have suitable food and habitat and will usually become a nuisance.

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