What’s the most beautiful swallow in North America? That’s a matter of opinion, of course. But more than one author — from John James Audubon to Florence Merriam Bailey — has been moved to superlatives in describing the Violet-green Swallow.
Of course, no shade of green can be described accurately as “violet-green.” Technically this species should be called the “Violet-and-green Swallow,” to denote the colors of the upperparts; but the current name has been firmly entrenched since the 1830s, and it’s unlikely to change.
Among North American swallows, the Violet-green is most closely related to the Tree Swallow. Both have iridescent colors on the back and bright white underparts, and both nest in tree cavities or similar kinds of holes. But while the Tree Swallow is common from coast to coast, the Violet-green Swallow is strictly a western bird, breeding no farther east than far western Texas and the western edge of the Dakotas. Its summer range extends all the way from Alaska and the Yukon Territory south to south-central Mexico.
Although all swallows feed mainly on flying insects, Tree Swallows are well known for being able to survive on berries during cold weather, allowing them to winter in many parts of the southern United States. Violet-green Swallows, by contrast, seem to stick to an insect diet, so they must vacate regions with cold winters. Nonetheless, they return north very early in spring. In southwestern Arizona, for example, Violet-greens are mostly absent in November and December, but they start to return in numbers in the latter part of January.
Migration seasons are the time when these western swallows are most likely to wander to the east. Vagrant Violet-greens have been recorded in many eastern states and provinces, with an interesting seasonal split. Cape May, New Jersey, where legions of experts scrutinize every bird that flies past, has had multiple fall records. Elsewhere in the east, including North Carolina, Tennessee, Virginia, New York, Ontario, Maine, and Newfoundland, however, the species has been recorded several times in spring. Clearly this bird could turn up anywhere, and birders everywhere have reason to watch for it.
It can be hard to keep binoculars trained on a swallow in fast, erratic flight, but it’s well worthwhile to practice this skill, since it can greatly increase your chances of finding a rare swallow out of range. For a practiced observer, a Violet-green Swallow might stand out because of the pattern of its lower back, with white patches wrapping from the flanks up onto the rump and almost meeting in the middle. For a rare sighting, though, it would be necessary to confirm the ID by seeing the face pattern and other points, some of which are easier to discern when the bird is perched. See the photos and captions in this column for a discussion of all the relevant field marks for this elegant swallow.
Key field marks
- Short tail, square-tipped or slightly notched
- Violet lower rump and uppertail coverts (hard to see)
- White flank patches almost meet on rump
- Upper back moss-green
- White from throat extends up behind and above eye
- Bright white underparts
What to look for
Size and shape. One of our smallest swallows. Its short tail looks square-tipped when fully spread, slightly notched when folded.
Face pattern. Male has white curving up behind and above eye, sharply separated from dark crown. Female has more blurry face pattern, pale behind eye, but with dark mottling down onto cheeks.
Upperparts color. Upper back and wing coverts are moss-green, while lower rump and uppertail coverts are purple. Colors are brighter in males.
Rump pattern. White from belly extends up flanks and onto sides of rump, almost meeting in center of rump.
Underparts. Entirely bright white below, although some females have a dusky wash down to edges of throat.
Green is the dominant color on males of this species: a beautiful moss-green on the upper back and wing coverts, bronze-green on the head. Violet is much more limited: a band across the nape, often hard to see, and part of the lower rump and uppertail coverts. When the bird is perched, the folded wingtips often cover the lower back, hiding both the violet feathers and the white patches on the sides of the rump. However, the face pattern of the male is enough for a definite ID, with a clean division between the dark crown and the white wrapping around the eye. Females (next page) have a mottled face pattern unlike that of any other North American swallow.
With its solidly iridescent blue upperparts, this Tree Swallow is likely to be a male; but females 2 years old or older can look very similar, so we can’t be certain it’s a male unless it’s paired with a duller bird. Regardless, the face pattern is diagnostic for this species, with a sharp horizontal cutoff between dark and white positioned just below the eye. We might be tempted to use the color of the upperparts — blue on Tree Swallow, mostly green on Violet-green — as a field mark, but iridescent colors can be notoriously tricky under changing light conditions, and some Tree Swallows (especially females) can show strong greenish tints on the back.
Unlike the Tree Swallow, in which fully adult females can look identical to males, female Violet-greens almost always are distinguishable from males by face pattern. It’s somewhat variable, but this bird perched at the entrance to its nest cavity shows a typical pattern. The head is dull brownish, with pale mottling extending up behind and above the eye and dusky mottling extending far down onto the cheeks — very different from the crisp division of white and dark on the male’s face. The colors of the upperparts on the female are variable also; many show fairly bright green and violet, almost always with some gray feathers mixed in.
This Tree Swallow is probably a 1-year-old female; older females show more iridescent blue on the upperparts, and they can be just as brightly colored as adult males. In every plumage, however, the sharp and distinct horizontal division between the white throat and the dark face and cap makes for a good field mark, never duplicated by the Violet-green Swallow. Notice also that the end of the tail falls even with the wingtips on this perched bird. Wing length averages about the same on Tree and Violet-green Swallows, but the Violet-green is a smaller, shorter-tailed bird, so its wings look proportionately longer, extending well past the tail tip when perched.
When swallows are in mixed flocks, as often happens over water or during migration, Violet-greens might be picked out partly by their small size and rapid, fluttering wingbeats. However, a definite ID requires more concrete evidence than impressions of size and flight style. At a distance, the thing to watch for is the rump pattern: The white from the underparts extends up through the flanks and onto the sides of the rump, often appearing practically to meet in the middle. To confirm the ID, especially for a bird outside its normal range, it would be necessary to see the face pattern, which differs between females and males but always looks different from that of the Tree Swallow.
The best-known field mark for Violet-green Swallow is the way the white flank patches wrap up onto the sides of the rump. But Tree Swallows also have white notching up high on the flanks, behind the wings, and this can be quite conspicuous, as seen in this photo. This can be enough to mislead a person who is overly eager to find a Violet-green Swallow. Eastern birders who don’t get to see Violet-greens regularly can prepare for the experience by watching Tree Swallows closely, studying how their markings appear at different angles. A basic principle of bird ID is that someone who wants to find rare birds should begin by becoming thoroughly familiar with the common species.
Many species of swallow have relatively broad ranges, surviving under a variety of conditions. This is partly because of their generalized food source, flying insects caught in midair, available in practically any warm climate. The Violet-green Swallow provides a prime example of adapting to a wide range of environments.
Because temperature is partly linked to elevation, many species of plants and animals live at low elevations in the north and much higher to the south. Violet-green Swallows are common breeders near sea level in Alaska; in the Southwest and Mexico in summer, most are in the mountains, up to 9,000 feet or higher. Most, but not all. Some pairs nest in holes in cliffs at low elevation along the lower Colorado River, and others nest in holes in giant cactus in southwestern Arizona and along the coast in northwestern Mexico.
From the cool aspen and spruce groves of Alaska to the blazing heat of cactus forests in the Mexican desert, the Violet-green Swallow displays a tolerance for an extreme range of conditions in the breeding season. But that raises a question: Since it’s so adaptable, why hasn’t it expanded its range into eastern North America, into areas that seem climatically identical to parts of its current range? Is it kept in check somehow by competition with Tree Swallows? This question would be worthy of study.
This article was first published in the May/June 2022 issue of BirdWatching Magazine.