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Tachycineta thalassinaviolet-green swallow

By Ashley Sanchez

Geographic Range

Violet-green swallows (Tachycieneta thalassina) are native to the Nearctic and Neotropical regions. They naturally have been found in western Northern America and Mexico including Baja California. Violet-green swallows breed in parts of the United States and Alaska and they migrate mostly along the Pacific Coast; this includes inland California and Washington. Besides the Pacific Coast, violet-green swallows also breed in western Utah, Colorado, Arizona, Idaho, southwest New Mexico and Texas. However, violet-green swallows have an eastern breeding range limit in the Rocky Mountains, which occur in eastern Idaho, Utah and northern New Mexico. In Canada, violet-green swallows breed in the following provinces: British Columbia, Alberta, the Northwest Territories, and Yukon. They also breed in Alaska, but mostly along the Gulf of Alaska and Chukchi Sea. When violet-green swallows are not migrating, they reside in Mexico. These birds can be found widely distributed in any area of Mexico with suitable nesting cavities, which includes areas both with small human populations areas and with large human populations. Baja California is typically a non-breeding area. (Shirling, 1935; Sibley, 2016)

Habitat

Violet-green swallows typically live in open environments near bodies of water such as meadows, rivers, marshes, shorelines, ponds, swamps and lakes. These types of environments generally have mosses that cover the ground and vegetation that allows moisture to be retained within the tree canopy. This is important to violet-green swallows, as they primarily feed on aerial insects that depend on moist soil to survive; lack of moist soil can result in a drop in insect populations and consequently affect populations of this species. Violet-green swallows nest in cavities throughout a wide range of habitats. In Mediterranean woodland environments, such as those in California, they can use decaying trees or holes constructed by woodpeckers to build their cavity nests. In Alaska, they typically nest in trees along coastlines and in artificial nesting boxes when available. In areas such as Mexico, where violet-green swallows can remain year round, they can nest in a wide variety of both urban and rural areas. This is because Mexico is surrounded by a multitude of nesting cavities such banks of small ravines, dead pines, residential homes and businesses, and various other man-made structures. (Gullion, 1947; Hobson and Sealy, 1987)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams

Physical Description

Both male and female violet-green swallows are small birds, with an average body size of 13 cm and forked tails. When these birds perch their wings are significantly longer than their tails. They have slender, pointed bills that they use to catch insects on wing. From afar, adult males appear to have dark-green rumps and white throats. However, in close proximity males have greenish-tan backs and iridescent violet rumps, with white throats and green crowns. Adult males and females are similar with the exception that adult females have light-tan crowns and overall smaller heads and bills. Females also have less well-defined green backs with dusky bluish auricular feathers. Juvenile violet-green swallows tend to have patches of white located on both sides of their rumps to indicate sexual immaturity. (Brown, 1983)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    13.8 to 14.5 g
    0.49 to 0.51 oz
  • Average length
    13 cm
    5.12 in
  • Range wingspan
    10.7 to 11.4 cm
    4.21 to 4.49 in
  • Average wingspan
    13 cm
    5.12 in

Reproduction

Violet-green swallows form monogamous mating pairs for the entirety of a breeding season, working together to build their nests and care for offspring until they are fledged. Occasionally, females may exhibit promiscuous behavior, mating with more than one male in a mating season. (Brawn, 1990; Shirling, 1935)

Violet-green swallows typically travel in late March to April to their breeding sites, where they form pairs and breed - usually only once per breeding season. During courtship, males compete for nest cavities and use various calls and displays to attract the female attention. Sometimes when a female approaches a nest, the resident male will respond aggressively until they identify that the bird approaching is female. In order to form pair bonds, males and females engage in courtship displays together. Once a male and female form a pair bond, they work to gather nesting materials such as twigs, grass stems, and feathers to build a cup-shaped nest in a cavity. If a breeding pair cannot find a proper nesting cavity, they will try to usurp a nest site. Nest construction can take anywhere from 3 to 20 days and average nest cup size is 7.62 cm wide.

Copulation normally occurs in May, after pairs build their nests, and females lay eggs towards the end of June. These birds are typically monogamous during the breeding season, but researchers have observed some females to mate with multiple males. Violet-green swallows have an average of 5 eggs per clutch, with females laying 1 egg per day, on average. Eggs are pure white without any markings and are 1.1 to 1.3 cm wide and 1.5 to 2.0 cm in length. Incubation occurs for several weeks before chicks hatch. Young violet-green swallows leave the nest about 22 to 24 days after they hatch. (Brawn, 1990; Shirling, 1935)

  • Breeding interval
    Once per breeding season
  • Breeding season
    April to July or August
  • Average eggs per season
    5
  • Range time to hatching
    2 to 3 weeks

Violet-green swallows provide both male and female parental care to their hatchlings. Males actively guard their nests to avoid being cuckolded. Females will forage for food to provide for chicks. Both spend time incubating their eggs. (Beasley, 1996)

Lifespan/Longevity

Wild violet-green swallows have an average lifespan of 6.8 years. In comparison, if they are raised in captivity, they have a longer average lifespan of about 7.4 years. The oldest captive violet-green swallow was 9 years old. Environmental factors and diet play a critical role in the lifespans of violet-green swallows. Some stress factors that affect violet-green swallows include habitat loss, reduced food quality, and climate change. (Edson, 1943)

  • Average lifespan
    Status: wild
    6.8 years
  • Range lifespan
    Status: captivity
    9 (high) years
  • Average lifespan
    Status: captivity
    7.4 years

Behavior

Violet-green swallows are social birds that form foraging flocks outside of breeding season. These flocks can be very large, comprised of several hundred birds. As a member of the swallow family (Hirudinidae) they are territorial during the breeding season and both sexes guard their nests against competitors. Despite this intraspecific aggression, they may breed in groups, but this depends on available resources. Violet-green swallows preen and sunbathe excessively to avoid getting parasites. They bathe by flying over and gently brushing the surface of the water with their feathers, then flying upwards to shake the water off. Violet-green swallows can also use rainfall to bathe. (Blem and Blem, 2000)

Communication and Perception

Songs - Not much is known about the vocalizations of violet-green swallows. However, these birds are grouped with other songbirds. Their song vocalizations have been closely associated with tree swallows, but with a sharper and harder chirp.

Calls - Violet-green swallow use interactive social call also known as "chee-chee" calls. An interactive social call occurs when an individual violet-green swallow interacts with another bird. This can be a social encounter with a bird of either sex. This can happen while they are foraging, chasing prey, or choosing a mate. Juvenile birds also make this call when they are hungry, suggesting that it is associated with parent-juvenile recognition. The "chee-chee" call can either be mono- or bi-syllabic with a frequency of 2.5 to ≥7.0 Hz and a interval range of 85 to 165 ms. The average duration of monosyllabic calls is 165 ms and thefor bisyllabic calls it is 125 ms.

Violet-green swallows can also make "twitter" calls. These calls are associated with flight, territorial establishment, and courtship displays. These calls are monosyllabic with a frequency of 2.0 to 6.5 Hz. The duration, repetitive pattern, and interval spacing of this call type is currently unknown. Additionally, "chee-chee" and "twitter" calls have been associated as alarm calls to signal distress, food begging, anxiety, pleasure, and territory proclamations. (Brown, 1983)

Food Habits

A food study was done on violet-green swallows in Arizona, Oregon, Colorado, and California from the months of March to September. The study showed that violet-green swallows maintained a primarily insectivorous diet. However, violet-green swallows from California had an extremely small portion of their diets consisting of oats and carrot seeds. Researchers suggested this was an anomaly and it was most likely that an ant was carrying the seed and consequently the violet-green swallows ate the seed. Consumption of beetles (order Coleoptera) accounted for 10.57% of the diet in this study. Ants (super-family Formicoidea) accounted for 9.42% of the Violet-green Swallow diet but were only eaten from May to September. Violet-green Swallows ate wasps and bees (order Hymenoptera) every month except April and this accounted for 17.48% of their diet. Additionally, 3.12% of their diet included small moths and caterpillars (order Lepidoptera). Violet-green swallows ate parasitic species, such as gallflies, but did not eat honeybees. The average size of prey that violet-green swallows targeted was less than 5 mm in length. (Beal, 1918; Garlick and et al.,, 2014)

  • Animal Foods
  • insects

Predation

Violet-green swallow eggs and hatchlings are vulnerable to predation by bears (genus Ursus), American Crows (Corvus brachyrhynchos), American Kestrels (Falco sparverius), snakes (suborder Serpentes), and mammals (class Mammalia) such as raccoons (Procyon lotor). Adult violet-green swallows are susceptible to predation in flight by hawks, falcons and kestrels. Adult violet-green swallows respond to such predation by mobbing any birds of prey that are within their nesting habitat. Both hatchling and adult violet-green swallows can become infected with parasites. If eggs and hatchlings are overcome with a substantial infection, parents will abandon the infected nest and leave the offspring to die. ("Violet-green Swallow", 2011; "Violet-green Swallow", 2017)

Ecosystem Roles

Violet-green swallows affect the populations of the insects they consume. This is important because they provide a natural form of pest control. Violet-green swallows are also cavity nest builders, which provides shelter and breeding areas for insects, reptiles, mammals and other bird species. ("Violet-green Swallow", 2011; "Violet-green Swallow", 2017)

Commensal/Parasitic Species
  • Mallophagial feather lice and Internal parasites

Economic Importance for Humans: Positive

Violet-green swallows prey on insects that eat human food crops such as fruit orchards and vegetable fields would be overrun by insects if not for these natural pest exterminators, thus contributing to a healthy ecosystem. This pest control also may reduce the cost of pesticides.

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

There is no known negative impact that violet-green swallows have on the human population.

Conservation Status

Violet-green swallows have recently experienced population declines of approximately 28% from 1966 to 2015. It is thought that this population decline may be a result of similar declines in aerial insect populations due to insecticides, global warming, and pollution.

Despite this population decline, violet-green swallows are still considered a species of "least concern" on the IUCN Red List. They are protected under the U.S. Migratory Bird Act and have no special status on either the U.S. Federal List or CITES. (Nebel, et al., 2010; Sauer, et al., 2017)

Contributors

Ashley Sanchez (author), California State University, San Marcos, Tracey Brown (editor), California State University, San Marcos, Galen Burrell (editor), Special Projects.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

bog

a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

male parental care

parental care is carried out by males

marsh

marshes are wetland areas often dominated by grasses and reeds.

migratory

makes seasonal movements between breeding and wintering grounds

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

scrub forest

scrub forests develop in areas that experience dry seasons.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

suburban

living in residential areas on the outskirts of large cities or towns.

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

tundra

A terrestrial biome with low, shrubby or mat-like vegetation found at extremely high latitudes or elevations, near the limit of plant growth. Soils usually subject to permafrost. Plant diversity is typically low and the growing season is short.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

visual

uses sight to communicate

References

2017. "The North American Breeding Bird Survey, Results and Analysis 1966–2015" (On-line). Accessed May 12, 2020 at https://www.mbr-pwrc.usgs.gov/bbs/.

2011. "Violet-green Swallow" (On-line). Accessed May 12, 2020 at https://www.allaboutbirds.org/guide/Violet-green_Swallow/lifehistory.

2017. "Violet-green Swallow" (On-line). Accessed May 12, 2020 at https://www.allaboutbirds.org/guide/Violet-green_Swallow/id.

Beal, . 1918. Food Habits of the Swallows: A Family of Valuable Native Birds. Washington D.C.: U.S. Dept. of Agriculture. Accessed May 12, 2020 at https://www.biodiversitylibrary.org/item/190620#page/3/mode/1up.

Beasley, B. 1996. “Males on Guard: Paternity Defences in Violet-Green Swallows and Tree Swallows.”. Animal Behaviour, 52: 1211-1224.

Blem, C., L. Blem. 2000. . “Effects of Some Meteorological Variables on Basking Behavior in Violet-Green Swallows.”. Journal of Field Ornithology, 71: 339-344.

Brawn, J. 1990. “Interspecific Competition and Social Behavior in Violet-Green Swallows.”. The Auk, 107: 606-608.

Brown, C. 1983. “Vocalizations and Behavior of Violet-Green Swallows in the Chiricahua Mountains, Arizona.”. The Wilson Bulletin, 1983: 142-145.

Edson, J. 1943. “A Study of the Violet-Green Swallow.”. The Auk, 60: 396-403.

Garlick, N., et al.,. 2014. “An Assessment of Nestling Diet Composition in the Violet-Green Swallow (Tachycineta Thalassina).”. Northwest Science, 88: 49-54.

Gullion, G. 1947. “Use of Artificial Nesting Sites by Violet-Green and Tree Swallows.”. The Auk, 64: 411-415.

Hobson, K., S. Sealy. 1987. “Foraging, Scavenging, and Other Behavior of Swallows on the Ground.”. The Wilson Bulletin, 99: 111-116.

Nebel, S., Mills, McCracken, Taylor. 2010. Declines of aerial insectivores in North America follow a geographic gradient. Avian Conservation and Ecology, unknown: unknown.

Sauer, J., Niven, Hines, Ziolkowski Jr, Pardieck, Fallon, Link. 2017. The North American Breeding Bird Survey, Results and Analysis 1966–2015. USGS Patuxent Wildlife Research Center, 2.07: unknown.

Shirling, A. 1935. “Observations on the Violet-Green Swallow.”. The Wilson Bulletin, 47: 192-194.

Sibley, D. 2016. Sibley Birds West: Field Guide to Birds of Western North America. unknown: Alfred A Knopf.

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