Tips for Identifying Bell’s Vireo

At 58, his notoriety already ensured by the publication of his great birds of america, John James Audubon left in 1843 for a last expedition in search of new birds. Traveling up the Missouri River with a team of young naturalists, he found species new to him, including a few that were new to science. One of these novelties was a vireo which he named in honor of expedition member John G. Bell, “an excellent companion in our not without peril treks”.

Audubon’s crew first encountered the vireo near what is now St. Joseph, Missouri, and continued to find it as they traveled upstream in the Dakotas. Typically, it was near the river in “the lowlands, overgrown with low shrubbery, or along the edges of ravines” in the grasslands. The species still mainly nests near shorelines or in shrubs along dense thickets.

Its habitat often makes Bell’s Vireo difficult to see. Luckily it has a distinct song – a quick, confused cheedledoo-cheedlededle-dee? . . . cheedledoo-cheedlededle-doo! This little song makes it easy to identify when it sings. But a silent bird, especially one migrating away from its breeding grounds, can be quite difficult, as it is an exceptionally simple bird with few obvious markings.

This simplicity can be a field mark in itself. A first step is to rule out other birds, such as a juvenile Verdin or a really dull warbler, noting its distinctive beak shape. But among North American vireos, its weak wingbars and weak face are unique.

The Bell’s Vireo is divided into four subspecies, with a curious distribution. The Midwestern breed has a breeding range that extends from Texas north to the Dakotas and sparingly east to Ohio. Another race breeds in western Texas and southern New Mexico. Arizona’s race spills over into southeastern California and extreme southwestern New Mexico. Finally, there is the “Least Bell’s Vireo” of southwestern California.

Birds from the Midwest look different from those from California and Arizona: more colorful, with a stronger wash of olive on the back and yellow below, and a noticeably shorter tail. They often hold their tail still or gently rock them up and down, but California and Arizona birds often flip their tail, side to side or up and down, like a gnat. Birds from western Texas and southern New Mexico most resemble those from the Midwest, though slightly duller and longer-tailed.

The Californian race is classified as endangered, and almost throughout their range, Bell’s vireos are birds of conservation concern. They have been badly affected by cowbird parasitism – in some studies up to 90% of vireo nests contained brown-headed cowbird eggs – and by destruction of riparian habitat. Fortunately, cowbird control and habitat restoration projects have helped local people bounce back.

Bell’s Vireo, California Race. April in San Diego County, California. Photo by Brian E. Small

Bell’s Vireo, California Race. The birds that breed in southwestern California and northern Baja represent an endangered subspecies often referred to as the “Lesser Bell Vireo”. Despite the name, this breed is not noticeably smaller than the Arizona form, but is grayer, showing barely a hint of color in spring and summer. The most similar species is the gray vireo, which also has low wingbars and a fairly long tail. However, the gray vireo has a narrow, full, non-diffused, broken white eyering like Bell’s, and is usually found in juniper woodlands, not streamside thickets. Other ID contenders like Plumbeous Vireo have stronger wingbars. Indeed, Bell’s vireos in the west are more likely to be confused with non-vireos, such as gnatcatchers.

Bell’s Vireo, breed from the Midwest. April in Galveston County, Texas. Photo by Brian E. Small

Bell’s Vireo, race from the Midwest. Widespread in the Midwest, this form (called “Eastern” in some books) looks especially similar to the California and Arizona subspecies. Its shorter tail gives it a different overall shape, and on average it is more colorful, with olive on the back and yellow on the sides and flanks. However, the facial pattern is the same everywhere, faint but distinctive. It shows an off-white eyering, stronger above the eye than below, and a short, pale supercilium, mostly above the lores in front of the eye. While breeds from California and Arizona often wag their tails in the manner of a midgecatcher or Bewick’s wren, the Midwestern breed tends to hold their tail still or gently wave their tail upwards. down.

Bell’s Vireo, breed from the Midwest. April in Galveston County, Texas. Photo by Brian E. Small

Bell’s Vireo, race from the Midwest. Wingbars are important terrain marks for many birds, but we shouldn’t simply note whether a bird has them or not. There are many degrees of variation. In this April photo, most of the large secret feathers have narrow whitish tips, creating a thin wingbar. The pale tips of the median coverts are barely visible, for only a hint of a second. If we saw this vireo in cooler plumage in late fall, the two wingbars would be more apparent; if we saw it in worn plumage in summer, it would appear to have little or no wingbar. On this Midwestern individual, compare the colors and tail length to the California bird pictured below.

Bell’s Vireo, California Race. December in Baja California Sur, Mexico. Photo by Brian E. Small

Bell’s Vireo, California Race. Photographed on wintering grounds in southern Baja, this Bell’s vireo almost certainly belongs to the California-breeding subspecies, or “lesser bell’s vireo.” It shows a stronger color tint than what we usually see on this run, but that’s probably based on the December date. The species undergoes a complete moult in late summer, so individuals are in their coolest plumage in fall and early winter. When they return north in the spring and when they sing on the breeding grounds in early summer, their colors are faded and California birds may appear completely gray. We must always consider the time of year and the effects of shedding, wear and fading on subtle birds like these.