Kevin T. Karlson
Posted: June 17, 2013, 5:00 p.m. PDT
Blackpoll Warbler by PJTurgeon (Own work), via Wikimedia Commons
When I think of global nomads, several highly migratory species come to mind. Arctic Tern, Hudsonian Godwit and American Golden-Plover travel more than 15,000 miles each year. Godwits and plovers are strong, robust creatures with powerful wings that carry them long distances over water, while Arctic Tern is a graceful, wind-catcher that can land on the water and rest during its legendary journeys from the Arctic to the Antarctic.
An unlikely companion to these long-distance migrants is the Blackpoll Warbler (Setophaga striata), a passerine that weighs 8 to 10 grams on average and sports a physical appearance suggesting a long-distance capability of only several hundred miles, like its warbler cousins. Along the evolutionary curve, however, this small bird decided to migrate from its high northern boreal nesting grounds to the wilds of the Amazonian Basin and other locations in South America. In fact, small numbers have been documented wintering as far south as southern Chile and Argentina, which represent the southernmost records of any North American migrant warbler.
Some might argue that a migrant warbler wintering in South America is not that unusual because many Neotropical wintering warblers make the journey each year. While this is true, a qualifying factor that separates Blackpoll from other warblers is the route it takes to reach its winter destination. Most warblers travel between 200 and 400 miles each night during migration, with stopovers to fatten up between flights. Blackpolls, fitted with radio transmitters, have been documented to fly nonstop for more than 1,200 miles from the southeast coast of the United States to the northern portion of Venezuela.
Equally astounding, the birds often double their body weight for this flight, building up a fat reserve that burns off during the journey. Imagine doubling your body weight for a nonstop marathon of several hundred miles and finishing (without food or water) at your original body weight! This physiological feat is beyond reach in the parameters of the human body.
Blackpoll is a medium-sized New World warbler (5 1/4 inches) that breeds across the boreal forests of North America from northern Alaska to the Canadian Maritime Provinces and Newfoundland. It is found breeding in the United States only on mountaintops in the southeastern portion of its range in New York and upper New England. It prefers the stunted habitat at the northern edge of the boreal forest zone across North America. In the maritime regions, it prefers stunted forest habitats associated with windblown areas.
Breeding microhabitats include cool, wet forests of low conifers, especially stunted red and black spruce and balsam fir. Other habitats include the edges of bogs and burned areas within taller coniferous forests. In the more western boreal regions, Blackpoll breeds in habitats dominated by deciduous trees and black spruces, including willows, alders and balsam poplars.
Blackpoll is somewhat of a sluggish, deliberate warbler and often feeds by gleaning insects from leaves and branches. In spring and on the breeding grounds, it tends to feed in the middle and upper levels of the canopy, rarely venturing outside the protective tree cover. A singing bird heard in spring migration in a coniferous tree can be difficult to locate, as many birders have experienced, due to its deliberate feeding habits. Conversely, Blackpoll Warbler tends to forage in low vegetation during fall migration, allowing birders very close looks.
Breeding male Blackpoll is one of only three black-and-white warblers in North America. (The other two are Black-and-white Warbler and Black-throated Gray Warbler.) The white cheek framed by a black cap and black moustache stripe is a distinctive field mark for the spring male Blackpoll. Spring females can be difficult to identify, especially when they forage 50 feet up in the treetops. They move quietly through the canopy, allowing for brief glimpses of plain, muted underparts. They can be quite variable but generally are olive above with black streaks and whitish below with blurry streaks against a yellowish wash to the breast and flanks.
The warbler as a whole is somewhat stocky, with a relatively short tail and long wings. Good identifying features in spring are orange legs and feet, which no other warbler of similar plumage displays. Both male and female exhibit two white wingbars.
Blackpolls in the fall can be tricky to identify, because they closely resemble Bay-breasted and Pine Warblers. Males and females in the fall mostly resemble spring females but have less defined streaks on the breast and flanks with more muted upperparts. Fall birds are mostly olive above with dark streaks, yellowish on the throat and breast, and white on the lower belly and undertail coverts. Most birds cannot be confidently aged or sexed in fall plumage. Another problem in the fall occurs in young birds, which sometimes do not show orange legs and feet but only orange on the soles of their feet. When confronted with one of these tricky birds, try to see the bottom of the feet while the bird is moving on a branch.
Spring migration from South America is mainly over the western Caribbean, although most birds appear to overfly the southern islands. Blackpoll is numerous during spring migration in the Bahamas, and most birds move into North America through Florida. An April fallout in Florida can contain more than 100 Blackpoll Warblers. Small numbers of Blackpolls occur on the Texas coast in spring. Most spring migrants move up the Atlantic Coast in April and occur in large numbers from mid- to late May in the northern mid-Atlantic states.
Fall migration is more easterly than spring migration, with Blackpolls uncommon in the midwestern states south of the Great Lakes. Banding data suggests that a portion of Blackpoll Warblers take off from the Atlantic Coast north of Cape Hatteras, North Carolina, on a nonstop overwater flight to South America. Blackpolls are among the most numerous "eastern" warblers in the fall in the western U.S. They are recorded in all the western states except Idaho, and California averages more than 100 birds each year during fall migration.
Given the hardships associated with the long-distance journey that Blackpoll Warblers undertake each year, it is amazing that this creature is one of the more abundant warblers seen in migration. Factors that contribute to its success include remote breeding areas undisturbed by man and no reliance on the cyclical populations of spruce budworm for breeding success.
Even with these positive factors, it is still one of the miracles of the avian world for this tiny creature to travel such long distances nonstop over water each year. I stop and admire each Blackpoll Warbler as I think about the incredible journey that this bird makes.
Mating — usually monogamous. A female pairs with the dominant male in her nest territory. Some males mate with many females, who show strong nest tenacity and mate with a male closest to their previous nest sites even if he is already paired. This polygymous behavior occurs in 10 percent to 30 percent of males.
Nest Sites — usually a stunted spruce or other coniferous tree 2 to 7 feet tall but as high as 33 feet. The nest is built against the trunk, supported by horizontal branches.
Nest — The female builds the bulky nest with bark, conifer twigs and dried grass and lines it with feathers.
Clutch — The clutch size is four to five eggs in a monogamous relationship and three to four eggs in a polygynous relationship. Usually only one brood is raised per season, but occasionally two broods occur.
Incubation Period — For 12 days on average, the female incubates the white to off-white eggs with lavender and brown marks.
Nestling Period — Both male and female feed the nestlings for about 12 days.
Food — mostly insects and spiders, occasionally berries and seeds, especially during migration