Blackpoll Warbler

The breeding plumage Blackpoll Warbler has grayish upperparts marked with black, white undertail coverts, and two white wing bars.

Males have a black crown and white cheek patch, with black streaking along the flanks.  Length: 5 in.  Wingspan: 9 in.

Females have a greenish head marked with black, and some thin, black streaking on the flanks.

Fall and winter birds are much duller, mostly lacking black on the head and underparts and having a greenish-yellow hue to the throat and upperparts.

Immatures are similar to fall adults.

Blackpoll Warblers inhabit coniferous forests and alder thickets. During migration, a variety of woodlands are used.

Blackpoll Warblers eat insects and berries.

Blackpoll Warblers forage deliberately along treetop branches, sometimes flycatching.

Photograph © Glenn Bartley.

Blackpoll Warblers breed from Alaska across central Canada and the far northeastern U.S. They winter in South America. The population may be declining.

More information:

Bent Life History

Visit the Bent Life History for extensive additional information on the Blackpoll Warbler.

Blackpoll Warblers make a nonstop flight over water from the northeastern U.S. to South America each fall, a distance that requires about 72 hours of continuous flight and entails very significant pre-flight weight gain followed by weight loss.

Blackpoll Warblers have very rarely hybridized with Bay-breasted Warblers.

The song is a series of high, consistent notes. A short, buzzy flight call is also given.

The Blackpoll Warbler’s nest is a cup of bark, twigs, weeds, and moss and is lined with feathers and finer materials. It is placed on a horizontal branch near the trunk of a tree.

Number: Usually 4-5.

Color: Whitish with darker markings.

Incubation and fledging:
The young hatch at about 12 days and fledge at about 11-12 days, though remaining dependent on the adults for some time.

Published by the Smithsonian Institution between the 1920s and the 1950s, the Bent life history series of monographs provide an often colorful description of the birds of North America. Arthur Cleveland Bent was the lead author for the series. The Bent series is a great resource and often includes quotes from early American Ornithologists, including Audubon, Townsend, Wilson, Sutton and many others.

Bent Life History for the Blackpoll Warbler – the common name and sub-species reflect the nomenclature in use at the time the description was written.

The common or vernacular name black-polled warbler owes its origin to the conspicuous and distinctive black crown of the adult male. The beginner, when first learning to differentiate the warblers, is likely to~ compare the blackpoll with the black and white warbler, since these two birds have the same color combination and lack the bright colors of many of the other species of warblers. In the autumn, however, it is hard for him to believe that the little greenish birds are the same black and white warblers he saw in spring.

The black-polled warbler is a very successful species in its competition with others. Although it encounters many hazards on its very long migration, and countless numbers meet death at this time, it has nevertheless been able to maintain a large and growing population. Anyone who has experienced seeing the great migration waves that arrive late in the season will agree that it is one of our most abundant warblers. One reason for this is the extensive breeding range in the seclusion of the northern coniferous forests stretching across the entire continent from Alaska to the Labrador coast. To be sure, the unusual numbers in eastern United States during the migration are due in part to the fact that the black-polled warblers, breeding in the extensive region to the north, pass in an ever narrowing migration route to their exit at the Florida Peninsula. In spring a reverse condition exists in which the birds spread out as they go north to occupy the great fan-shaped area.

Spring: This warbler arrives late in the season, at a time when the majority of the trees are in blossom or well leaved out, and since it often frequents the taller tree tops it is sometimes difficult to see, but the frequent songs give evidence of its presence. The blackpoll is deliberate in its movements and usually unsuspicious and approachable. Often during the height of the migration I have seen them along fences and stone walls and even in open fields and pastures searching for food and going about their business apparently unaware of my presence. At times they appear in my garden and backyard, in fact they seem to be in evidence everywhere I go. Then at night, if I am stationed in a quiet place, I hear their characteristic highpitehed calls as, high in the air, they journey on their way.

Migration: The blackpolls migrate chiefly at night, and since they are readily attracted by bright lights during their flight, we often find concentrations of them in the parks of our larger cities, where they are reported as being seen under the electric lights at night. When daylight comes they naturally seek out places such as parks and public gardens where trees and shrubs provide temporary resting and feeding places. In Central Park, New York City, for example, G. E. Hix (1905) states that the black-polled warbler outnumbers all others put together.

The black-polled warbler winters in northern South America. Birds in migrating to North America may follow a route along the coast of Central America and Mexico, as does the cliff swallow, or they may fly directly over the Caribbean via Cuba and the intervening islands to Florida, the route invariably chosen by the blackpoll. It reaches the Florida coast about April 20, and as it is one of the latest to migrate it seldom reaches the Gulf States before the last week of April. It proceeds leisurely and may be seen long after the majority of other warblers have passed on their way to their nesting grounds. On this part of its migration it travels at a rate not exceeding 30 to 35 miles a day and does not reach southern New England and the northern tier of Central States until about May 15. The individuals that cross the upper Mississippi Valley through Minnesota and the Dakotas then greatly accelerate their pace to about 200 miles per day so that a week later they have reached the central part of the Mackenzie Valley and by May 30 they arrive at the far distant breeding grounds in northwestern Alaska. This long distance is covered in about the same time that the slower-moving eastern contingent arrives in southern Quebec and Newfoundland. About 25 to 30 days are required to travel the distance of 1,000 miles from Florida to Minnesota, whereas the final lap of 2,500 miles is accomplished in less than two weeks. This remarkable change in speed can be correlated with the fact that the advance of spring in the northern interior is much more rapid than it is in the Mississippi Valley and Gulf coast. In the northland spring comes with a rush, and during the height of migration the temperature of the Mackenzie Valley is about the same as it is in Minnesota.

The black-polled warbler breeds principally in Canada and none farther south than southern New Brunswick, the mountains of the northeastern states and in the Rocky Mountains. This means that no blackpoll migrates a distance of less than 2~500 miles, while those individuals that winter in Brazil and nest in northwestern Alaska must travel more than 5,000 miles to reach their nesting grounds. These are straight-line distances, and do not take into account the deviations in the course or the random flights in search for food.

The migration route of the blackpoll from Alaska has been evolved over a long period of time. It is apparent that this bird extended its range from the eastern part of North America to northwestern Alaska. Instead of using the Pacific flyway it retraces its journey across the mountains and moves southeastward over the ancestral route to leave the United States for South America through a funnellike exit by way of Florida. In Arkansas, Louisiana, and the southern part of the Mississippi flyway it is a comparatively rare bird.

In autumn the blackpoll begins leaving its outpost in Alaska in August and, as in spring, it moves more rapidly over the northern section of its journey. After it reaches the States early in September its speed is less pronounced. These warbiers are among the last to leave; they may be seen in the United States throughout September and October, and the last individuals do not leave Florida until November.

The distribution of this warbler is not uniform over the entire area included in the migration, and the details of its course taken in spring may vary from that followed in autumn. T. D. Burleigh (1934), in a study of the distribution and abundance of the black-polled and baybreasted warbiers in the southeastern States during the spring and fall migrations, notes that at Athens, Ga., and in the Piedmont region in general the blackpoll is an abundant spring migrant but in the fall is exceedingly scarce. Likewise at Asheville in the mountains of North Carolina, it is an abundant spring migrant and completely absent in autumn. On the coast it is common only in fall. Mr. Burleigh states: “It apparently, in the west to east migration in the fall from its brceding grounds in the far northwest, is moved by some impulse to reach the coast as soon as possible, and as a result it is at best merely a straggler over much of the area it occupies in the spring migration.”

Swales and Taverner (1907) have noted that the black-polled warbler, though one of the most abundant fall migrants in southeastern Michigan, is conspicuously absent in the region of Detroit, Wayne County, in spring. No explanation is offered to account for this peculiar situation in that section of its migration journey.

The fall migration of the blackpolls as it occurs in the White Mountains of New Hampshire is of interest. These birds breed commonly in the upper Canadian Zone mainly above 3,000 feet on southern exposures and down to 2,000 feet on the northern slopes. During September they swarm in migration over the low country of the southern part of the State and beyond, but in the valley bottoms among the mountains they are rare. Here they migrate mainly at the upper levels and along the mountain tops. The tendency to migrate at the higher elevations along mountain ranges has been observed in other sections of the migration course. On September 15, 1900, Glover M. Allen (1903) observed a great flight of black-polled and myrtle warblers starting at 4: 30 a. m. and continuing for 2 hours in the White Mountains. Several hundred birds passed, of which threefourths were blackpolls. These warbiers came flying in from the south, high in the air, making straight for Carter notch, a great rift in the mountain with a valley opening out toward the north and another to the south. “It seemed,” Dr. Allen writes, “as if the blackpoll warblers from all of the forests immediately to the south were moving north in a concerted manner to pass through the notch and off beyond. Possibly they were heading for the Ammonoosuc Valley to continue thence down the Connecticut; this would be a natural course, and one cannot suppose that their northward flight at this season could have been more than some such local movement.”

Norman Criddle (1922) has taken migration records of the blackpoll over a period of 21 years at Aweme, Manitoba, Canada, where he finds the average date of appearance in spring to be May 14, with his earliest date on May 9, 1902. In autumn the average date of last birds seen was September 9, and the latest record was one observed on September 15, 1912.

The observations and dates of the spring and fall migration made by M. B. Trautman (1940) at Buckeye Lake, Ohio, are typical of the midwestern section of the migration route. iHe writes as follows:

The black-poll warbler was among the last of the warblers to make its appearance in spring. The latest date for spring arrivals was May 15. In the average year a few could be seen daily after May 15, and by May 18 the species was common. At the peak of migration, between May 18 and 27, 10 to 40 birds could be observed daily. The species then generally disappeared suddenly, for by May 29 all except a few stragglers had departed.

The first southbound transients were seen between August 31 and September 14, and the species was always rare until September 15. An increase became apparent by September 17, and from then until October 10 It could be regularly recorded. The peak of migration came between September 25 and October 10, and then 10 to 150 Individuals could be daily observed. A sharp decrease in numbers took place between October 10 and 15, and by October 23 the species was usually absent. * * *

The black-poll and bay-breasted warhlers were close associates during migrations. Both were late spring and fall transients, both chiefly inhabited trees, and their maximum numbers during migrations were almost equal.

In Maine and Massachusetts the main migration wave of blackpolls comes late in May, but a few forerunners can be expected during the second week of the month and a few exceptionally early records have been made during the first week. It is the only one of the transient warbiers that remains until June, and in some years a few belated stragglers linger after the second week in southern Maine. It nests in the northern part of the state.

In autumn the blackpolls arrive in force in September, with some forerunners appearing late in August. They are with us through September and much of October; in Massachusetts dates of last appearances have been reported for November, and one was seen as late as December 17, 1939, at Plum Island, Mass., by Richard Stackpole (1939) and others.

Nesting: The blackpoll is a bird of the northern spruce forests; in fact, the spruce seems to be an essential requirement for its nesting site. At Kent Island, Bay of Fundy, New Brunswick, I have seen 9 nests, all in small white spruces and all located within the narrow range of 2 to 7 feet from the ground and built snugly against the trunks of the trees. The somewhat bulky structures were well supported in each case by one or two horizontal branches. Most of these New Brunswick nests were well concealed from view by canopies of overhanging branches. A typical nest had an outside diameter of 41/2 inches and was 3 inches in depth. The internal dimensions of the cup were 2 inches wide and 1’/2 inches deep. The foundation was made of small twigs and sprays of spruce, pieces of bark, dried grasses, and weeds mixed with bits of moss, lichens, and wool. The interior of the structure consisted of plant fibers and fine rootlets, some hair, and a liberal lining of white gull feathers. The lining of feathers is characteristic, being as essential to the nest structure as the spruce tree is for a nesting site. The kind of feathers used, of course, depends on the kind that are available; on Grand Manan Island, New Brunswick, it is commonly goose feathers, in the Magdalen Islands in the Gulf of St. Lawrence, duck feathers; in Labrador, duck or ptarmigan feathers; and at Lost River in the White Mountains I have seen nests lined with grouse feathers and odd feathers of song birds. The myrtle warbler also uses feathers in lining its nest, which is more compactly built than the blackpoll’s and is generally placed on a horizontal limb away from the trunk of the tree.

J. P. Norris (1890a) describes 17 sets of eggs of the blaclipoll and gives the location of 15 nests collected on Grand Manan Island as follows: “They were all found in spruce trees, one of them was found only a foot from the ground; another was eighteen inches; a third two feet up; a fourth three and a half feet; two more were each four feet high; five were five feet up; two were seven feet from the ground; another was eight feet and still another was ten feet high.” William Brewster (1882a)~ describes a nest containing three eggs which he found in the Magdalen Islands on June 28, 1882:

The nest was built in a low, thick spruce, which stood on the edge of a swamp, near a brook. It was placed on a horizontal branch at a height of about three feet, and was well concealed by the clusters of densely-imbricated needles above. * * * The main body of the structure is composed of Usnea moss, weedstalks, and dry grasses, closely matted and protected outwardly by coarser stalks and a few dead spruce twigs. The lining is of slender, black moss-sterns (which curiously resemble horse hair) cow’s-hair and a few feathers. The whole affair is remarkably solid and bulky for a Warbler’s nest.

R. M. Anderson (1909) cites an exception to the rule that the blackpoll nests in trees saying of a nest he found June 24, 1908, on Moose Island near Fort Resolution, Great Slave Lake:

I stepped across a small dead spruce lying on the ground, and a small plainly colored bird darted from the mass of tall dead grass which surrounded the trunk of a fallen tree. The bird disappeared in the underbrush at once without uttering a sound. Concealing myself, I watched about twenty minutes and the bird stealthily approached the nest hopping from hush to bush, occasionally uttering a sharp, nervous t8ip like the alarm note of the Junco. The bird proved to be a female Blackpoll Warbler. The nest was placed directly on the ground in the middle of a clump of dead grasses, Immediately underneath a small, fallen spruce, the trunk of which was lying about ten inches above the ground. The nest was composed of dead grasses, mixed with cottony substances and a little moss, lined with finer grasses, and a few feathers including one tall feather of a fox sparrow. The four eggs were advanced in incubation.

R. MacFarlane (1891) found several nests of the blackpoll on the ground along Anderson River of northwestern Mackenzie well above the Arctic Circle. In the Mackenzie Delta region bordering the Arctic Ocean the blackpoll is found in dense alder thickets in gullies and ravines; nesting some distance beyond the tree limit. A. R. Porsild (1943) found a nest in an alder thicket near the water’s edge on the south end of Richards Island, off the Delta, on August 16, 1934. The nest contained many feathers and was lined with the down of Epilobiwin and willow.

At Kent Island, New Brunswick, the blackpolls usually arrive during the last week of May, and they may be heard singing or be seen feeding among the thick spruce growth which covers a large portion of the 2-mile-long island. Courtship and nest building is a slow deliberate proceedure and nests with eggs are not to be found before the second or third week of June.

The major part of nest building was performed by the female, in one instance under observation; the male was in full song during this time, and while he may have assisted in gathering nesting material I never saw him do any construction work at the nest. The nest contained one egg on June 16, 1932, but it was not until June 22 that the fifth and final egg of the set was laid. Two nests found by Ernest Joy, warden at Kent Island, contained one egg each on June 11, 1943. Each set of five eggs was complete on June 15, indicating that in these two cases an egg was laid each day untilthe sets were completed.

The female sits very closely when incubating; by moving cautiously I have approached within a few feet of the bird before she fluttered away. At the New Hampshire Nature Camp, Lost River, N. H., in the White Mountains, a blackpoll built a nest in a small spruce tree standing alongside a trail used frequently each day by numerous students. The incubating female paid no attention to passing persons unless they stopped to examine the nest more closely. When thus forced to leave the nest, she slipped off into the dense growth of spruces but emerged soon to utter sharp alarm notes. These calls invariably brought the male to the scene, and together they would protest the intrusion. The male guards his territory zealously and is ever ready to challenge a bird of his own kind or any stranger that appears in the vicinity. In addition to his singing and duties as guardian I have seen him bring food to the female at the nest. One of the best ways to locate a nest containing eggs is to follow a male carry. ing some larvae or insect to his mate. A nest of course can be quite easily located in this manner after it contains young, by watching either parent.

Dr. Herman R. Sweet made a study of nesting black-polled warbiers at Kent Island during the summer of 1933. His arrival at the island was too late to observe their behavior during courtship, nest building, or incubation, save for 2 hours spent in the blind erected within 4 feet of the nest, on June 29, the day before the eggs hatched. During the 2 hours the female incubated the eggs for a total of 92 minutes, in five periods. The shortest time spent incubating was 11 minutes, and the longest 25 minutes, the average being 18.5 minutes. I have noted that other incubating warbiers often exhibit considerable restlessness toward the end of incubation and at this time leave the nest more frequently and for longer periods of time. Presumably the same may have been true of the blackpoll observed by Dr. Sweet.

When not on the nest the female could be heard flying about in the nearby trees searching for food, but she made not the least sound when approaching the nest. She invariably came to the nest from a lower level and after reaching the base of the reclining spruce in which it was located hopped up to the nest. While incubating she often dozed with her eyes shut, but upon hearing the least sound she suddenly became alert.

Eggs: Complete sets of black-polled warbler eggs vary from three to five, but four or five are more usual. The eggs have a white or light creamy buff or sometimes a pale greenish ground color, with brown and umber specks scattered over the whole surface and numerous spots and blotches of reddish brown and subdued shades of lilac and lavender concentrated at the larger end, sometimes forming a wreath.

The weights and measurements of a set of eggs found on Kent Island, June 28, 1932, were taken by Dr. Sweet as follows: 1.7 by 1.4 cm., 1.8 gin.; 1.9 by 1.35 cm., 1.8 gin.; 1.85 by 1.7 cm., 1.7 gin.; 1.85 by 1.9 cm., 1.9 gin. The average of 77 eggs collected by J. P. Norris (1890a) is .72 by .54 inch. Of this series the eggs showing the four extremes measure .79 by .54, 73 by .55, .68 by .49, and .69 by .47 inch. The average of 15 eggs collected by P. B. Philipp (1925) is .70 by .55 inch; the largest measures .74 by .56, and the smallest .66 by .54 inch. A set of eggs collected by N. S. Goss (1891) on June 19, 1880, at Grand Manan, New Brunswick, were unusually large, with the following measurements: .77 by .55, .78 by .56, .78 by .56, and .79 by .56 inch.

The measurements of 50 eggs average 17.9 by 13.4 millimeters, the eggs showing the four extremes measure 21.8 by 13.7, 18.3 by 14.7, and 16.3 by 12.7 millimeters (Harris).

Young: The incubation period of the blackpoll is at least 11 days, but the exact time was not determined because it was not possible to ascertain the exact date when incubation started. Apparently it may start before the set of eggs is completed, for in one instance 2 days elapsed between the hatching of the first and last of five eggs.

After the young appear the adults exhibit even less fear of a human observer. At Lost River, N. H., on June 30, 1932, I stood in full view, within 5 feet of a nest to take pictures of the adults feeding the young. The female was not in the least disturbed by my presence, but the male at times displayed some reluctance in coming directly to the nest. Both male and female feed the young, but often the male would present his mate at the nest with a larva, which she would accept and in turn feed it to the young. A~ first small green larvae and aphids were fed to the young but by the time they were 6 days old spiders and large adult insects also were delivered. The nest was always kept clean; the fecal sacs were eaten or carried away as soon as they appeared. As is true of many other passerine birds, the adults after feeding a youngster may stimulate it with a gentle stroke of their beak, causing the fecal sac to appear.

The following observations are from the unpublished notes of Dr. Herman Sweet on black-polled warblers nesting at Kent Island. On June 30, 1933, three of the eggs l~atcbed, one in the morning at 9 :40 a. m. the other two at 7:45 p. m. A fourth egg, which was cracked, failed to hatch and was removed by the following morning. One of the three young died and was removed by Dr. Sweet on the second day. At the time of hatching, the natal plumage consists of delicate tufts of grayish down located on the head, humeral, crural, alar, and caudal tracts.

The first young to hatch opened its mouth widely for food as soon as it was free from the egg although the adults were not present to stimulate such behavior. After this occurred, both the female and male arrived at the nest but neither had food for the young. The male left the nest at once and the female left later, to return in 5 minutes without food. After brooding the lone young for 11 minutes she left again and returned in 5 minutes with a green larva. The larva was minced in her bill and fed to the young just 43 minutes after it had left the shell. The female brooded 5 minutes then left in search of more food. This procedure was repeated six times during the period of observation 9 :40 to 11 :08. The female brooded 63 minutes or 71.4 percent of the time. The longest single period was 21 mmutes and the shortest 5 minutes. Of the six times she left the nest she returned with food four times. During observations made between 2 and 3 p. m. the female did not make any feedings, although she left the nest occasionally. One of the remaining eggs was pipped at this time.

At 7: 45 p. m. two more eggs had hatched and the shells had been removed. At 7: 59 the male appeared at the nest; the female sat on the rim while he fed the young a minced green caterpillar. He left in 25 seconds and the female again brooded. At 8 :12 the male was hack again with more larvae. This time the female paid no attention to his presence. The male then uttered a soft twittering sound, where upon she hopped up on one side of the nest and he fed at least one young. At 8:45 p. m. a flashlight was turned on the nest. She raised up her breast, inspected her young and then settled down for the night.

On July 2, when 2 days old, the young had developed noticeably, with feather papillae showing on ventral tracts. On the following day feather papillae also appeared on the caudal, alar, crural, and hurneral tracts, and tail. None had yet appeared on the head and femoral regions. On July 4, at 4 days, sheathed feathers appeared on all tracts except the head. When the male came to the nest to feed the young, if they did not open their mouths he uttered a tweet to which they all responded. The young twittered weakly when fed. On July 5 their eyes were open and the feathers on the caudal and ventral tracts were beginning to unsheath at their tips.

As the young grew larger and acquired their juvenal plumage at 8 or 9 days, they frequently stood on the edge of the nest when alone and went through gymnastic exercises by flapping their wings, thus gaining strength in preparation for the time of their first flight. They also frequently preened their rapidly growing feathers to assist in removing the sheaths.

At 10 days, the young exhibited distinct signs of fear. The following day the nest was empty: (By the eleventh day, in another nest under observation, two of four young had left the nest.) The adults continued to feed the young in the vicinity of this nesting site for several days, after which the entire family disappeared from the scene.

Plumages: Jonathan Dwight, Jr. (1900), has described the plumages and molts of the blackpoll as follows:

[Juvenal plumage] above, including sides of the head, olive-gray obscurely streaked or mottled with dull black. Wings and tail, clove-brown edged with dull olive-green, whitish on the tail, tertiaries and wing bands. Two rectrices with white terminal spots on the inner webs. Below, dingy white mottled with dull black. Bill and feet pinkish buff, the former becoming dusky, the latter sepia.

First winter plumage ucquired by a partial postiuvenal moult in July and August in eastern Canada, which involves the body plumage and the wing coverts, but not the rest of the wings and the tail.

Similar to previous plumage but unspotted. Above, including sides of head, olive-green, olive-gray on tail coverts, rather obscurely streaked, chiefly on the back, with black. The wing coverts clove-brown edged with olive-green and tipped with white, yellow tinged. Below, very pale canary-yellow, white on abdomen and crissum with a few obscure grayish streaks on the throat and sides. A narrow and obscure superciliary line and orbital ring pale canary yellow, the lores whitish, a faint dusky transocular stripe. One or two black crown feathers are occasionally assumed.

Resembles D. castaaea and D. vsgorsji but distinguishable from either of them by the streaked back and duller colors.

First nuptial plumage acquired by a partial prenuptial moult which Involves most of the body plumage, the wing coverts and tertiaries, but not the rest of the wings nor the tail. Young and old become indistinguishable. The black cap and black and white plumage are assumed, at first evidently, somewhat veiled by whitish edgings.

Adult winter plumage acquired by a complete postnuptial moult in July. Similar to first winter dress but whiter below, the streaking often distinctly black and extending to the chin, which is spotted here and there; above the crown Is decidedly streaked or marked with stray black feathers; the wings and tail are blacker and the edgings are darker and grayer especially on the tertiaries. The slight sprinkling of black feathers is like that found in DoliMonyr orizivorue and some other species In the autumn.

[Female] * * * plumages and mooRs correspond to those of the male, from which it is first distinguishable in first winter plumage, but not in every case. Females are then a little greener above and yellower below including the crissum, the streaks on the side extremely faint. The first nuptial plumage acquired by moult is a little paler than the first winter, the head, back and sides with distinct black streaks; resembles the male in first winter dress but more decidedly streaked. The adult winter plumage is practically indistinguishable from the first winter but rather paler and with the wing edgings darker. The adult nuptial plumage much resembles the male In adult winter dress and Is merely tinged with yellow and streaked on crown, back, sides of chin, and sides with black. The black cap and broad streaking of the male are never acquired.

The fall or winter plumage of the blackpoll is so similar to the first winter plumage of the bay-breasted warbler that even the most experienced field observers find them extremely difficult to differentiate during the fall migration. This confusion has often lead to errors in field identification, so that reports of the relative abundance and distribution of these two species during the fall migration are sometimes confusing.

The upper parts of the blackpoll are duller and more streaked, the wings are edged with a yellow-green in place of gray-green; the underparts are yellowish instead of huffy. These differences are not constant, and some individuals of the bay-breasted warbler can be distinguished only by the trace of chestnut on the flanks and under tail coverts. Perhaps the best field mark is the color of the legs, which in the blackpoll is light, approaching a yellowish, while in the baybreasted warbler it is dark brown and in some instances almost black. It is true these warbiers are more deliberate in their movements, offering better opportunities for detailed observation, but even so, positive identifications are often impossible in the field.

Concerning the postjuvenal molt and the acquiring of the fall or winter plumage E. A. Preble (1908) writes of blackpoll warblers observed and collected in the Mackenzie region of northwest Canada.

The blackpoll occurs In summer throughout the region north to the very edge of the wooded country. It arrives on its breeding ground late in May, and some individuals are on their way south again in late July, molting as they travel, into the olivaceous plumage common to old and young In autumn. * * * Birds of the year taken July 19, 23, and 29 are in the spotted Juvenal plumage, but with the yellowish-green of the fall plumage [first winter] appearing on the hack, throat, chest, and sides; the change was about half completed in most of the specimens. An adult taken July 26 also is molting, the yellowish-green forming a patch on each side of the breast. Took specimens in the transition from the breeding to the autumnal plumage near Lake St. Croix, August 14, when the species was abundant.

An immature female blackpoll that I collected on the mainland west of Nain, Labrador, on August 12, 1934, represents a transitional state between the juvenal and first winter plumage, with feathers of each plumage about equally represented. Another specimen, a male taken near the same place on August 18, 1937, has its winter plumage practically completed. At Lost River, in the White Mountains of New Hampshire, I have seen young in various stages of transition from the juvenal to the first winter plumage during the last week of July.

Alexander Wetmore (1936), who has made counts of the number of contour feathers of passeriforin and related birds, found that a male blackpoll weighing 17.6 grams, taken October 15, 1933, had 1,583 contour feathers with a total weight of 1.2 grams.

S. P. Baldwin and S. C. Kendeigh (1938) have made the following weighings of black-polled warbiers: 1 adult taken in May, 12.4 gin.; 3 males taken in September average 11.4 gin.; 1 female taken in Septeinber, 12.8 gin.; 3 immature birds taken in September average 11.5 gin.; and 4 in October average 13.9 gin.

Albinistic plumages of the black-polled warbler apparently are not rare. J. Harris Reed (1888) describes the plumage of a male taken May 12, 1888, at Upper Chichester, Delaware County, Pa., as follows:

The entire crown, with the exception of three or four small black feathers over the eyes, is pure white, the edges of the feathers tipped with cream color which is more decided fringing the neck. The upper tail-coverts and rump are pure white, extending high up on the back and passing irregularly through the interseapulars and joining the white on back of neck and crown; rather silky across the rump. The interscapulai~s form an irregular bar across the shoulders. The scapulars and tertiaries are sparsely spotted with white, most prominent on the right side. The sides of breast are streaked as usual, although of a rusty color, rather obsolete as they approach the chin which Is pure white. The throat and breast are ochroleucoas. Otherwise the plumage is natural. * * * The white feathers are immaculate from the quills out, none being edged or spotted with the natural colors.

Charles H. Townsend (1883) states that a black-polled warbler in the Academy of Natural Sciences of Philadelphia has the entire plumage suffused wit.h white, and William Dutcher (1888) found a perfect albino blackpoll killed by striking Fire Island light on September 23, 1887. Other cases of pure and partial albinisin have been reported, indicating that this abnormality may be expected.

Food: Anyone who has observed the blackpolls during migration and especially in their nesting haunts in the coniferous forests is well aware of their insect-feeding habits. Not only do they glean the leaves and twigs of insects and their larvae, but frequently they dart out from the concealment of the foliage to capture some passing flying insect with a sharp snap of the bill, after the manner of the flycatcher. At Kent Island, New Brunswick, I have frequently seen them on the terminal branches of the spruce trees feeding upon the spruce gall lice and other insects which infest these trees. All the food that I have seen eaten by the adults or delivered to their young during the nesting season consisted wholly of insects and spiders.

The blackpoll, like many other species of insect-eating birds, may at times neglect its usual food to take extraordinary numbers of those species which, for any reason become superabundant for a time, thus this bird serves well in doing its part to extirpate serious local infestations of insects. E. H. Forbush (1907) cites a case in which warblers completely eliminated an infestation of plant lice as follows:

I have had several opportunities, within the last fifteen years, to watch the checking of Insect uprisings hy hirds. One morning in the fall of 1904 I noticed in some poplar trees near the shore of the Musketaquid a small flock of myrtle and black-poll warbiers, busily feeding on a swarm of plant lice. There were not more than fifteen birds. The insects were mainly imagoes, and some of them were flying. The birds were pursuing these through the air, but were also seeking those that remained on the trunks and branches. I watched these birds for some time, noted their activity, and then passed on, but returned and observed their movements quite closely all day. Toward night some of the insects had scattered to neighboring trees, and a few of the birds were pursuing them there; but most of the latter remained at or about the place where the aphids swarm was first seen, they were still there at sundown. The swarm decreased rapidly all day, until just before sunset It was difficult to find even a few specimens of the insect. The birds remained until it was nearly dark, for they were still finding a few insects on the higher branches. The next morning at sunrise I went to the trees to look for more specimens. The birds, however, were before me, I was unable to find a single aphis on the trees.

S. A. Forbes (1883) made an investigation of the food eaten by birds found in a 45-acre apple orchard, in Illinois, heavily infested with cankerworms. Of the birds collected and their stomach contents examined, four blackpolls had eaten cankerworms to the extent of 67 percent of their stomach contents. In addition there were boring bettles (Psenocerus), 15 percent; other Coleoptera (beetles), 4 percent; ants, 4 percent; gnats 4 percent; traces of Hemiptera and mites; and some undetermined seeds. Samuel Aughey (1878) studied the food of Nebraska birds during the great invasion of Rocky Mountain migratory locusts on the weste.rn prairies and plains during the period 1873: 1876. The blackpoll was prominent among the birds ~vhich preyed upon the locusts. Of four blackpoll stomachs examined, each contained an average of 30 locusts and 12 other insects; no seeds, grains, or other food was found. Sylvester D. Judd (1902) made a special study of the birds on a Maryland farm. On May 13: 15, 1900, he observed blackpolls feeding on mayflies at the top of a cedar tree so heavily infested that it was gray with these insects, On May 17 he also found these warbiers doing their part in suppressing an infestation on pine trees by sawflies (Pteronus). The stomachs of 11 specimens collected on the farm revealed that they had also eaten freely of ants, weevils, wasps, and bees. The blackpoll warbler has been known to feed ravenously on winged termites at times when these insects appear in immense swarms. There are numerous reports that in the far north these birds devour hundreds of troublesome mosquitoes.

In fall the blackpoll eats a few seeds and berries, such as the pokeberry (Phytolacca americana), but they are mainly insectivorous at all seasons. ïWhen passing through Florida in autumn they devour large numbers of spiders and their eggs, plant lice, and scale insects found on the citrous and native plants. It is obvious that the blackpoll is useful as an insect-eating bird arid that they often play an important role in suppressing insect infestations.

Voice: Late in May in New England after the host of warNers have arrived and many of them have passed on their way, we may expect to hear the unpretentious, high-pitched, insectlike but characteristic song of the black-polled warbler. It is in full song when it arrives and continues to sing throughout its stay, one of the most frequently heard warbler songs at that season. Its song is not musical, but the ebb and flow of its rapidly uttered series of high-pitched, accented syllables is most agreeable. it sings on the average only two or three times a minute, and seldom more than four times a minute, but in any favorable woodland there are sure to be several individuals singing, so that the song is always in evidence. Although these birds may be well hidden by the foliage, the song always assures one of their presence, but it is not always easy to trace to its source, as it has certain deceiving ventriloquial qualities.

Aretas A. Saunders (1941) gives his analysis of the black-polled warbler’s song as follows: “The song of this bird is weak, high-pitched, and much like those of the Bay-breast and Black and White in quality. The commoner form of song is a series of notes all on the same pitch and in even time, but growing louder in the middle and softer again to the end. The number of notes varies from six to eighteen, and the notes are sometimes slow and measured and at other times quite rapid. In a less common form the notes are so rapid as to be uncountable, and the song becomes a trill, swelling in loudness in the middle.”

Ralph Hoffmann (1904) in describing the song writes: “It is a high thin t8it tsit t8jt tsit tsit, of a penetrating quality, delivered with a crescendo and diminuendo; the last notes are by some birds run rapidly together with almost a sputtering effect.”

Rev. J. H. Langille (1884) states: “That song, th~.ugh one of the most slender and wiry in all our forests, is as distinguishable as the hum of the Cicada or the shrilling of the Katydid. Tree-tree-treetree-tree-tree-tree-tree, rapidly uttered, the monotonous notes of equal length, beginning very softly, gradually increasing to the middle of the strain, and then as gradually diminishing, thus forming a fine musical swell. * * * There is a peculiar soft and tinkling sweetness in this melody, suggestive of the quiet mysteries of the forest, and sedative as an anodyne to the nerves.”

On their nesting grounds in the White Mountains of New Hampshire and at Kent Island, Bay of Fundy, New Brunswick, I have heard the full song of the blackpoll throughout the nesting season but rarely after the young left the nest. I have seen them perched in full view at the very top of a spruce or fir tree pouring forth their simple but earnest song. They have a call note, a high-pitched lisp which resembles zeet, and when suddenly surprised or alarmed they utter a strong chirp.

The blackpoll is usually silent in autumn, but at times it has been heard in full song late in the season, after having acquired its winter plumage. During the fall migration the diurnal note tsit is the cornm~nest heard.

Though the blackpoll does not excel as a songster, its song has one characteristic which makes it stand out in marked contrast to all others. Albert Brand (1988), who determined the vibration frequencies of 59 passerine birds, found that the song of the blackpoll has the highest pitch of all the bird songs he studied. Its average frequency was 8,900, midway between C sharp 8 and D 8, or over an octave above the highest tone on the piano. The blackpoll also produced the highest avian frequency studied, 10,225, a quarter tone under E 8. The lowest frequency recorded in various songs of the blackpoll was 8,050. By comparison, the mean frequency in songs of the northern pine warbler is 4,150, the highest 5,125, and the lowest only 3,300. Indeed the song of the blackpoll is of such a high frequency that it is well beyond the range of hearing of many persons. I must admit, in recent years, I have observed the blackpoll singing and could see by its posture and the movements of its beak and throat that it was singing, but Iwas unable to hear the song.

Enemies: The blackpoll is subject to the usual enemies of other woodland birds, but all these apparently exact an insignificant toll when compared to the hazards experienced during migration. In crossing the wide expanses of the Caribbean Sea from the winter quarters in South America, some of them take refuge on passing boats during bad weather, but the vast majority after battling adverse winds and storms reach th~ Florida and Gulf coast in a weakened or exhausted condition. C. J. Maynard (1896), who landed April 27, 1884, on a small key in the Bahamas, found great numbers of black1)0115, some of which he found dead apparently due to exhaustion.

W. E. D. Scott (1890) in writing of the spring migration at Tarpon Springs in 1888 states:

It is so rare that one finds any hirds dying or dead from other than accidental causes, generally connected in some way with innovations caused by the settlement of a country, as telcgrat)h wires, light-houses, and the like, that it seems worth while to give the following details of an epidemic. It was apparently conlined, as far as I am aware, to the representatives of this species alone, and only to those individuals which visited the Anclote Keys and Hog Island. These keys are four In number, and are four miles from the main land, in the Gulf, and extend in a north and south line for about twenty-five miles. I found in late April and early May many D[cndroica] .9triota dead, and others apparently Ill unto death on these islands. * * * I picked up dead on April 29, 1885, in a short walk on South Anclote Key, upwards of twenty-five.

Scott presents no evidence of disease or cause of the so-called epidemic, and I am inclined to believe these birds were members of a late migratory wave that had met with adverse conditions and died of exhaustion.

The habit of migrating at night is indirectly a cause of great mortality when waves of these birds encounter lighthouses and lighted towers. Often vety serious conditions prevail during cloudy or foggy nights when the birds, losing their bearings and attracted by the bright light, descend from their high-level flight and are dashed to death on striking some part of an illuminated tower. William Dutcher (1888) writes that of the 595 birds killed by striking the Fire Island Light on Long Island on September 23, 1887, no less than 356 were blackpoll warbiers.

W. E. Saunders (1930) has reported great destruction at the Long Point Lighthouse, Ontario, on Lake Erie, during September 1929. On September 7 there were 31, on September 9, 6 and on September 24: 29, 199 blackpolls that met their death by flying into the light. Similar conditions prevail along the Maine coast where during cloudy and stormy nights many warblers, including a large percentage of blackpolls, are killed.

High towers such as the Washington Monument also exact a heavy toll on night-flying birds. Robert Overing (1938) reports that in the course of an hour and a hall, 10 :30 p. m. to midnight of September 12, 1937, 576 individual birds, chiefly warblers and including the blackpoll, were dashed to their death. At this time the humidity ranged from 65 to 75 percent, and a mist enveloped the top of the shaft. These and numerous other instances indicate that lighthouses and towers are a great menace to a night-migrating bird such as the blackpoll. Probably more individtials meet violent death in this manner than by any other way.

I have not been able to find any record of a case of parasitism of the blackpoll by the cowbird. This, however, is to be expected as the ranges of the two birds do not greatly overlap. The cowbird is of no importance in its relation to the life of this warbler.

DISTRIBUTION
Range: North America and northern South America.

Breeding range: The black-polled warbler breeds north to northern Alaska (Kobuk River and Fort Yukon) ; northern Yukon (La Pierre House) ; northern Mackenzie (Richards Island, Fort Anderson, Blackwater River, and Hanbury River); northern Manitoba (Lac du Brochet and Churchill); northern Quebec (Bush Lake, Fort Chimo, and Indian House Lake); and northern Labrador (Nain). East to the coast of Labrador (Nain, Cape Aillik, and Cartwright) and Newfoundiland (Fogo Island, Trinity, and St. John’s). South to southern Newfoundland (St. John’s and St. Pierre); Nova Scotia (Baddeck, Halifax, and Yarmouth); southern Maine (Calais, Waterville, and Auburn) ; southern New Hampshire (Tamworth and Peterborough); northwestern Massachusetts (Mount Greylock) ; northern New York (Mount Marcy and Leyden, rarely Slide Mountain in the Catskills); northern Ontario (Trout Lake) ; central Manitoba (Oxford House); central Saskatchewan (Cumberland House and Flotten Lake) ; central Alberta (Flat Lake, Stony Plain, and Hythe) ; and central and northwestern British Columbia (Summit Lake, Tatana Lake, and Atlin); southern Yukon (Carcross) and southern Alaska (Chitina Maraine, Lake Clark, and Nushagak). West to western Alaska (Nushagak, Bethel, St. Michael, Nome, and Kobuk River).

Winter range: The blackpoll winters in northern South America east to eastern Cayenne (Oyapock River). South to southern Cayenne (Oyapock River) ; western British Guiana (Roraima) ; southern Venezuela (Casiqujare) ; northwestern Brazil (Marabitanas) ; and north-central Ecuador (Sara-yacu). West to north-central Ecuador (Sara-yacu and Archidona) and western Columbia (La Morelia, Rio Frio, and the Santa Marta region).

Migration: L ate date of spring departure from the winter home is; Ecuador: Rio Suno, April 10. Early dates of spring arrival are; Cuba: Habana, April 24. Bahamas: Cay Lobos, April 15. Florida: Sombrero Key, April 14. Alabama: Barachias, April 22. Georgia: Milledgeville, April 11. South Carolina: Aiken, April 20. -North Carolina: Raleigh, April 16, Virginia: Lynchburg, April 18. West Virginia: Wheeling, April 31. District of Columbia: Washington, April 21. Pennsylvania: Jeffersonville, May 4. New York: Brooklyn, May 1. Massachusetts: Quincy, May 7. New Hampshire: East Weshnoreland, May 2. Maine: Portland, May ‘7. Nova Scottia: Halifax, May 15. New Brunswick: Fredericton, May 18. Newfoundland: Tompkins. May 17. Quebec: Montreal, May 18. Labrador: Cartwright, May 27. Louisiana: Grande Isle, April 20. Mississippi: Oxford, April 23. Arkansas: Winslow, April 22. Tennessee: Chattanooga, April 19. Kentucky: Russeilville, April 25. Indiana: Bloomington, April 28. Ohio: Cleveland, April 29. Michigan: Battle Creek, April 28. Missouri: Independence, April 27. lowa: Marshalltown, May 3. Wisconsin: Milwaukee, May 1. Minnesota: Red Wing, May 5. Kansas: Wichita, May 2. Nebraska: Red Cloud, May 1. South Dakota: Sioux Falls, May 3. North Dakota: Grafton, May 4. Manitoba: Aweme, May 6; Churchill, June 6. Saskatchewan: Regina, May 8. Mackenzie: Providence, May 16. Colorado-Boulder, May 6. Wyoming: Cheyenne, May 8. Montana: Great Falls, May 12. Alberta: MeMurray, May 8. British Columbia: Tetama Lake, May 22. Alaska: Bethel, May 20.

Late dates of the spring departure of transients are: Haiti: Gonave Island, May 15. Cuba: Habana, May 16. Bahamas: Andros Island, May 23. Florida: Daytona Beach, June 1. Alabama: Long Island, May 22. Georgia: Savannah, June 3. North Carolina: Raleigh, June 3. Virginia: Norfolk, June 7. District of Columbia: Washington, June 16. Pennsylvania: Haverford, June 10. New York: Far Rockaway, June 18. Massachusetts: Harvard, June 17. Lonisiana: Grande Isle, June 4. Mississippi: Deer Island, May 29. Tennessee: Nashville, June 2. Illinois: Chicago, June 9. Ohio-Cleveland, June 10. Michigan: Sault Ste. Marie, June 5. OntarioOttawa, June 12. Missouri: St. Louis, June 6. lowa: Grinnell, June 10. Wisconsin: Madison, June 13. Minnesota: St. Paul, June 9. Oklahoma: Copan, June 5. South Dakota: Faulkton, June 10. North Dakota: Argusville, June 10. Manitoba: Aweme, June 24. Saskatchewan, Indian Head, June 9. Colorado-El Paso County, June 1. Wyoming: Laramie, May 26. Montana: Great Falls, June 8.

Early dates of fall arrival are: Manitoba: Aweme, August 18. South Dakota: Yankton, August 8. Kansas: Lawrence, September 18. Ontario: Rainy River, August 5. Minnesota: Lanesboro, August 27. Wisconsin: Herbster, August 10. Iowa: Wall Lake, August 28. Missouri: Montier, August 29. Michigan: Detroit, August 20. Illinois: Glen Ellyn, August 23. Ohio: Toledo, August 14. Kentucky: Danville, August 31. Tennessee: Nashville, September 8. Louisiana: New Orleans, September 21. Vermont: Burlington, August 24. Massachusetts: Boston. September 1. New York: Rochester, August 28. Peunsylvania: Berwyn, August 20. District of Columbia: Washington, August 17. Virginia: Charlottesville, August 20. North Carolina: Chapel Hills, September 16. Georgia: Augusta, September 23. Alabama: Birmingham, September 7. Florida: Fort Myers, September 25. Bahamas: Walling Island, September 28. Dominican Republic: San Juan, Septemberï 27. Puerto Rico: Cartagena Lagoon, September 24. Barbados: October 20. Colombia: Santa Marta region, September 29.

Late dates of fall departure are: Alaska: Fort Yukon, September 18. Yukon: Macmillan Pass, September 7. British Columbia: Atlin, August 27. Mackenzie: Leith Point, Great Bear Lake, August 29. Alberta: Edmonton, September 25. Montana: Great Falls, October 3. Saskatchewan: South end of Last Mountain Lake, September 3. Manitoba: Churchill, September 6; Shoal Lake, September 26. North Dakota: Fargo, October 23 (bird banded). Nebraska: Hastings, October 16. Kansas: Lawrence, October 23. Oklahoma: Norman, November 8. Wisconsin: New London, November 4. Iowa: Davenport, October 4. Missouri: La Grange, October 13. Ontario: Ottawa, October 11. Michigan: Grand Rapids, October 29. Ohio: Youngstown, October 21. Illinois: Murphysboro, October 20. Tennessee: Nashville, October 23. Quebec: Fort Chimo, August 23; Montreal, October 6. Newfoundland: Cape Anguille, October 3. Maine: Bath, October 7. Vermont: Wells River, October 17. Massachusetts: Harvard, November 24. New York: Orient, November 20. Pennsylvania: Doyleston, November 7. Virginia: Lexington, October 28. North Carolina: Raleigh, November 6. South Carolina: Mount Pleasant, November 14. Georgia: Athens, November 1. Florida: Clewiston, November 24. Bahamas: Watling Island, November 9. Puerto Rico: Cartagena Lagoon, November 26.

Casual records: The blackpoll has occurred several times in Greenland. In 1853, one was shot near Godthaab; a juvenile was collected in Isua Lichtenfelsfjord on October 14, 1911, and two more were taken there late in the same month; on October 15, 1911, another juvenile was shot near the Isua copper mine in the Ivigtut District; and on September18, 1919, a juvenile was shot near Narssarmiut in the Sukkertoppen District. Several occurrences in Bermuda have been recorded: one was seen March 12 to 15, 1901; six were seen October 12, 1929; and one was seen October 21, 1929. On June 17, 1858, an adult male was collected at Collico near Valdivia, Chile. It has been surmised that this may have been an escaped cage bird.

Destruction: Lighthouses and high buildings have, at times, taken heavy toll of the black-polled warbler and this species is nearly always on the list of those striking. At Sombrero Key, Fla., they have been reported to strike the lighthouse from April 14 to May 20 and from September 25 to November 16. The highest number striking in spring was on May 19, 1887, when 60 birds struck the light, of which half were killed. The fall migration takes a heavier toll, for on the night of October 14, 1887, 160 blackpolls struck, of which 95 were killed, and during the four nights October 14 to 17, 124 birds were killed out of 322 that struck the light. Blackpolls have been reported as seen about the light at Montauk Point, N. Y., from September 29 to October 27, but no figures are available as to the nmnber killed. At Fire Island Light on the night of September 23, 1887, of the 595 birds that were killed, 356 were blackpolls. In the fall of 1920 many were killed around the hght at Long Point, Ontario. From September 7 to 29,236 were killed; 199 of them between September 24 and 29. More lately, on the night of September 10, 1948, four blackpolls were killed by flying against the Empire State Building in New York City.

Egg dates: Alaska: 3 records, Jane 10 to 21.

New Brunswick: 38 records, June 10 to July 3; 23 records, June 12 to 20, indicating the height of the season.

New Hampshire: 11 records, June 16 to July 16; 7 records, June 20 to 28.

Quebec: 16 records, June 19 to July 4; 9 records, June 23 to 27 (Harris).