Blackpoll Warbler

The Blackpoll Warbler (Setophaga striata) is a New World warbler. Breeding males are mostly black and white. They have a prominent black cap, white cheeks and white wing bars. The Blackpoll breeds in northern North America, from Alaska, through most of Canada, and into the Great Lakes region and New England.

They are a common migrant through much of North America move down to winter in northwestern South America. They are rare vagrants to western Europe, although their northerly range and long-distance migration make them one of the more frequent transatlantic passerine wanderers.

Description

The Blackpoll Warbler is a fairly small bird which attains the weight of a ball point pen.^[2] However, it is one of the larger of the diverse Setophaga genus (formerly Dendroica). In the species, body length can vary from 12.5 to 15 cm (4.9 to 5.9 in) and wingspan can range from 20 to 25 cm (7.9 to 9.8 in). Body mass can vary from 9.7 to 21 g (0.34 to 0.74 oz), with an average bird anywhere between 12 and 15 g (0.42 and 0.53 oz). Among standard measurements, the wing chord is 6.6 to 8 cm (2.6 to 3.1 in), the tail is 4.5 to 5.4 cm (1.8 to 2.1 in), the bill is 0.8 to 1.2 cm (0.31 to 0.47 in) and the tarsus is 1.8 to 2 cm (0.71 to 0.79 in).^[3] The summer male Blackpoll Warblers have dark-streaked brown backs, white faces and black crowns. Their underparts are white with black streaks, and they display two white wing bars. The adult females essentially resemble washed-out versions of the summer males, and in particular, the females lack the strong head patterns, and their crowns and faces are shades of gray. Another outstanding physical characteristic of the species are the bright orange, pink legs.

Non-breeding birds of this species have greenish heads, dark-streaked greenish upperparts and yellowish breasts, with the yellow extending to the belly in young birds. Their wing bars are always present.

	Sound of the Blackpoll Warbler
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Habitat

In the southern portion of their breeding range, Blackpoll Warblers can be found on the higher elevations of mountains in woodland or brushy areas. They also spend their summers on the wooded coastal islands of Maine and the Maritime Provinces. Father North they have been reported throughout the boreal coniferous forest. Blackpolls breed nearer to the tundra than any other warbler.^[4]

Behavior

Although fairly large for a warbler, Blackpoll Warblers are fairly easy to miss because of their relatively inactive foraging style and tendency to perch in dense foliage near the canopy of the trees. They are more often heard than seen, though their song is one of the highest pitched known. Their songs are simple repetitions of high tsi notes. Their calls are thin sits.

Foraging and diet

The Blackpoll has a deliberate feeding style with occasional flitting, hovering and hawking around branches. They birds are primarily insectivorous. The species appears to be quite a generalist, preying on a great diversity of adult and larval insects and spiders. Documented insect prey for the species includes lice, locusts, cankerworms, mosquitoes, webworms, ants, termites, gnats, aphids and sawflies. It has been suggested that this species may be a spruce budworm specialist, but there is no obvious connection between population trends of the two species.^[5] The Blackpoll will opt for berries in migration and during winter. They often forage high in trees, and sometimes catch insects while in flight.

Reproduction

Their breeding habitats are coniferous woodlands, especially those in which spruce trees grow. These birds' breeding ranges extends to the taiga. Blackpoll Warblers commonly nest in a relatively low site which can be found in a conifer, and they lay 3–9 eggs in a cup-shaped nest, though most nest usually contain less than 5 eggs. The eggs are incubated for around 12 days and the young leave the nest when they are only 10 days old, before they can fly well. They are feed by the parents for a total of around two weeks. Mated females usually begin second nests right away and leave post-fledging parental duties to their mates. The high incidence of double brooding, coupled with (and partly a function of) low nest predation and parasitism rates, results in high annual productivity for this species.^[6]

Migration

Blackpoll Warblers have the longest migration of any species of New World warbler. This is likely the reason that are one of the later warblers to appear in spring migration, with a relatively prolonged movement through North America anytime from early May to mid-June. In spring, the peak of the species' migratory movement in late May, when most warblers are on their breeding grounds. They usually passage through in August and September during fall migration, a more typical timing.

Baird describes the Fall migration of the Blackpoll. From their breeding grounds across the northern latitudes, they converge on the Northeastern United States south to Virginia starting in mid-August.^[7] Part of the fall migratory route of the Blackpoll Warbler is over the Atlantic Ocean from the northeastern United States to Puerto Rico, the Lesser Antilles, or northern South America. To accomplish this flight, the Blackpoll Warbler nearly doubles its body mass in staging areas and takes advantage of a shift in prevailing wind direction to direct it to its destination. When they fly southward over the Atlantic they burn, according to Baird, .08 grams of fat every hour. This route averages 3,000 km (1,900 mi) over water, requiring a potentially nonstop flight of around 72 to 88 hours. They travel at a speed of about 27 mph (43 km/h). Blackpolls can weigh more than 20 g (0.71 oz) when they leave the United States and lose 4 or more grams by the time they reach South America. Some of the Blackpolls land in Bermuda before going on. Some birds, often with lower body weights, don't make it.^[8]

Scientific studies and discussion

The Blackpoll Warbler's transoceanic flight has been the subject of over twenty-five scientific studies. Sources of data include radar observations, bird banding and weights taken, dead birds recovered from field sites and fatal obstacles.^[9]

Island stopovers at Bermuda and other places have been cited as evidence of migratory pathways. Baird's conclusion, stated above, differed from Cooke (1904, 1915) and Murray (1965, 1989).^[10] Cooke and Murray contended that the Blackpoll Warbler migrates to South America along the mainland of southeastern North America. Baird, Nisbet and others argued that most Blackpoll Warblers fly directly from northeastern North America over the Atlantic Ocean to their winter range. They used data from nocturnal accidents, banding stations and sightings to state that Blackpoll Warblers are rare autumn migrants south of Cape Hatteras, North Carolina, whereas north of Hatteras they are common. Those holding to a direct oceanic pathway pointed to this evidence to support their hypothesis.^[11]

References

Bibliography

• New World Warblers by Curson, Quinn and Beadle, ISBN 0-7136-3932-6
• Blackpoll Warbler. The Cornell Lab of Ornithology: All About Birds. Access: May 20, 2011
• Baird, James (1999). Returning to the Tropics: The Epic Autumn Flight of the Blackpoll Warbler in Kenneth P. Able's Gathering of Angels. Ithaca, New York: Cornell University Press, pp. 63–78.

External links

Wikimedia Commons has media related to Blackpoll Warbler.

Wikispecies has information related to: Setophaga striata

• Blackpoll Warbler Species Account – Cornell Lab of Ornithology
• Blackpoll Warbler – Dendroica striata – USGS Patuxent Bird Identification InfoCenter
• Stamps for: Grenada, Guyana at bird-stamps.org
• Blackpoll Warbler videos, photos, and sounds at the Internet Bird Collection
• Blackpoll Warbler photo gallery at VIREO (Drexel University)