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Photo by Dick Cannings
Photo Copyright Dick Cannings
Violet-green Swallow
Tachycineta thalassina
NatureServe conservation status
Global (G-rank): G5
State (S-rank): S4S5B
External links
General information
The violet-green swallow, Tachycineta thalassina, breeds in montane forests west of the Rocky Mountains from southern Alaska southward through western Canada to the Mexican highlands. It winters in Mexico, Guatemala, El Salvador, and Honduras. The violet-green swallow is commonly found throughout Utah during the summer. It resides in a variety of habitats, ranging from lowland valleys to mountain peaks, but typically it breeds in mid-elevation aspen forests where it can find an abundance of abandoned woodpecker cavities in which to nest. During spring and fall migrations, large mixed flocks of swallows are often seen around water bodies in lowland areas of the state.
Violet-green swallows feed exclusively on flying insects that are captured in flight. After individuals form pairs, both sexes investigate potential nesting sites, but it is the female that probably makes the final selection. Females also gather the majority of the nesting materials. Pairs nest in abandoned woodpecker cavities in standing dead trees, between rocks in a cliff, or in nest boxes provided by humans. The female incubates her clutch of four to six eggs for about two weeks. Both parents feed the young, but the female brings the majority of food to the nest. The young leave the nest after about twenty-four days, but they are still dependent on their parents for food for some time afterward. The forestry practice of removing standing dead trees reduces the availability of suitable nesting locations for this species.
Species range
Breeding range extends from the Yukon River valley in Alaska and central Yukon Territory and southwestern Alberta south through southern Alaska, British Columbia, southwestern Saskatchewan, Montana, southwestern South Dakota, and northwestern Nebraska to southern Baja California and the northern mainland of Mexico, and through Colorado and western Texas (Bent 1942, Brown et al. 1992, Sinclair et al. 2003). Recent range extensions have been reported in the northeastern part of range (e.g., Saskatchewan, Canada; Wright 1992, Houston 1999). During the nonbreeding season, the range extends from central coastal and southern California and Mexico south regularly to Honduras, casually or accidentally to western Panama and Costa Rica (Terres 1980, AOU 1983, Stiles and Skutch 1989, Brown et al. 1992).
Migration
Migrates northward from wintering areas February-April (Terres 1980). Arrvies in northern breeding areas in April, depart in July in north, August-September farther south (Turner and Rose 1989).
Habitat
Open coniferous, deciduous or mixed forest and woodland, primarily in highlands (frequently at low elevations in north); in migration and winter also meadows, fields and watercourses, more commonly in highland regions (AOU 1983). May nest in cliff crevice, natural tree cavity, woodpecker hole, crevice in building, or bird box; also reported to use old nest of cliff or bank swallow.
Food habits
Feeds on flying insects (e.g., flies, leafhoppers, ants, wasps, bees, beetles, moths). Forages over ponds, fields, and wooded areas catching insects in flight. Occasionally may forage on ground on accumulations of insects such as midges or mayflies.
Ecology
2.5-15 breeding pairs per 40 ha in northern Arizona; up to 50 pairs per 40 ha in thinned forest with added nest boxes (Brawn and Balda 1988).
Reproductive characteristics
Egg dates: May-early July in south, beginning in late May in north. Clutch size typically is 4-5, sometimes 6, in north; smaller in south. Incubation, by female, lasts 13-15 days. Altricial nestlings are tended by both parents, leave nest in 23-25 days. Usually 1 brood per season, though 2 per season reported for Oregon. May nest in loose colonies if nest sites are abundant.
Threats or limiting factors
On a range-wide scale, no major threats are known. Locally, threats may include introduced nest-site competitors, nesting habitat loss, and extreme weather conditions. Introduced secondary cavity nesters, including the house sparrow and European starling, threaten nesting success by competing for suitable nesting cavities; these species often begin nesting prior to the violet-green swallow, so they have an advantage in site selection (Bent 1942, Erskine 1979, Brown et al. 1992). Removal of snags may have a strong negative impact on the species. In northern Arizona's ponderosa pine forests, this species was exclusively reliant on snags for nest-site locations (Cunningham et al. 1980, Brawn and Balda 1988). Clearing of forest for settlement and agriculture removes natural nest sites, as do forest harvest strategies that remove snags (Erskine 1979, Brawn and Balda 1988). This species is sensitive to extremely cold weather and accompanying low insect activity; large numbers of individuals have been found dead in emaciated condition after spring storms along migration routes (Bent 1942).
References
- Ehrlich, P. R., D. S. Dobkin, and D. Wheye. 1988. The birder’s handbook[:] a field guide to the natural history of North American birds. Simon & Schuster, New York. xxx + 785 pp.
- Behle, W. H., Sorensen, E. D. and C. M. White. 1985. Utah birds: a revised checklist. Utah Museum of Natural History, Occasional Publication No. 4. Salt Lake City, UT.
- Brown, C. R., A. M. Knott, and E. J. Damrose. 1992. Violet-green Swallow. Birds of North America 14.
