Yes, Virginia, there is a Santa Claus

By Bill Chaisson
Of a Feather
On Dec. 5 a Virginia’s warbler was spotted in Hampton, N.H. and six days later, according to the NH Bird Forum, it was still there. It was initially spotted along with an ash-throated flycatcher. Both of these are western migratory species who have no businesss being in New England at any time, let alone in early December. This phenomenon of seeing birds well outside their usual range is not a new one. When Roger Tory Peterson published his field guide in 1934, one of his innovations was to list “accidentals.” David Sibley followed suit and speckled his range maps with green dots to indicate wandering tendencies. A spectacular example of this kind of sighting occurred last year in the form of the Steller’s sea eagle that haunted the Northeast for months.

The warbler and the flycatcher are insect-eating birds that normally follow the weather southward to a place where their food supply remains animate through the winter. The occurrence of the Virginia’s warbler (Leiothlypis virginiae) is particularly odd, as this is a bird of rather specialized ecology and limited distribution in its natural range. It breeds between 6,000 and 9,000 feet in steep, dry, pine-juniper-oak woodlands between the Front Range of Colorado and the basin-and-range mountains of Nevada and from Idaho and Wyoming down into Arizona and New Mexico. Ordinarily it migrates to southern Mexico for the winter although it has been seen in southern California or Texas.

Ending up in coastal New Hampshire is quite far afield, but not unprecedented. It has been recorded as far east and north as Nova Scotia and Labrador and as far east and south as the Bahamas. This sort of wandering, or dispersal, is a primary way for a bird (or any mobile animal) to extend its range. It is very much a lottery approach, but then nearly all of evolution by natural selection is a long-shot strategy.

The western edge of the Virginia’s warbler breeding range is the Sierra Nevada along the California/Nevada border but in the 1970s it began showing up in the San Bernardino Mountains, west of Los Angeles. If this population reaches a critical mass, it could stabilize and constitute an observed extension of this species’ territory by several hundred miles. The San Bernardino Mountains have peaks reaching nearly 11,000 feet; they are sufficiently high to support the type of woodland favored by L. virginiae.

According to NH Bird Forum, the Virginia’s warbler seen earlier this month is the second sighting in the state, with the first in spring 2021. Interestingly, the latest one was foraging in junipers in Bicentennial Park. These are “eastern redcedars,” not a species it would encounter out west, but nonetheless a juniper. Birders have taken several photos of this individual, none of which show snow on the ground in Hampton. One observer even saw the warbler jumping up from the ground as if it were snapping at insects. There is no record of this species eating vegetable material. In other words, it had better start heading south soon.

The Hampton bird seems to be a lone individual that has gotten extremely off course during migration. It is not likely to be extending its range into New England. Some enthusiastic observers wondered if the Steller’s sea eagle would breed with a bald eagle. They are in the same genus and hybridization has been documented. This is not a method of starting a new species. Rather, it is generally considered a form of “genetic pollution” and a good way to eradicate a rare species (like the Steller’s sea-eagle).

Virginia’s warbler was described in 1858 by Spencer F. Baird, who named it after Virginia Anderson, the wife of the Army surgeon who collected the type specimen. In the 1960s one systematist lumped it, considering it to be a variant of the widespread Nashville warbler (L. ruficapilla), but in the 1970s it became part of a “superspecies” that included the Nashville, Virginia’s, Lucy’s (L. luciae), and Colima (L. crissalis) warblers on the basis of similar behaviors and vocalizations. (In the ‘70s they were classified in a different genus.)

A superspecies or “species complex” consists of very closely related species that may or may not hybridize. In this case there is a very small breeding range overlap between the Virginia’s and the Nashville on the northern and western sides of the former’s range. The Virginia’s and Lucy’s overlap in New Mexico and Arizona. But while the Virginia’s nests high up in the dry (deciduous) oak-juniper forest, the Lucy’s nests down in the riparian forests of evergreen oak, sycamore and ash.

The Colima warbler is larger and browner than the other three, but it has the rusty-red cap of the group and the yellow tail coverts of the Virginia’s. Like the Virginia’s, it favors oak-pine forests, but lower in elevation with a grassy understory. It also has a breeding range in the Chisos Mountains of Big Bend in Texas south through the Sierra Madre Oriental of Mexico that is disjunct from the other three members of the complex.

But, tellingly, all four have overlapping winter ranges. In fact, the Colima warbler is named for a small Mexican state where it winters. Lucy’s warbler is named for the daughter of Spencer Baird, who also named the Virginia’s warbler. Both of these species will be renamed by the American Ornithological Society within the next couple of years. Although Virginia Anderson and Lucy Hunter Baird seem to have led rather blameless lives, all common names of birds that honor people will be changed. The rules of scientific names are rather more fixed and those will remain the same, even if they commemorate the same people.

The general plan is to make names more descriptive. Male and female Virginia’s warblers are gray-green with a small rusty cap, white eye rings and yellow tail coverts. The males have variable yellow on the throat and chest. You name it.

— Bill Chaisson has been a birdwatcher for over 50 years. These columns are archived at shinhollow.wordpress.com.