Declines in the population of Cerulean Warblers in many parts of its range have made the species a focus of much survey and monitoring work. Cerulean Warblers are susceptible to forest fragmentation, although they will occupy second growth in addition to mature forest.
Male Cerulean Warblers typically arrive on their breeding grounds about a week before females. While males appear to help the female select a nest site, it is the female alone that builds the nest.
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Description of the Cerulean Warbler
The Cerulean Warbler has white underparts with dark streaks on the flanks.
Males have dark blue upperparts, head, and neck, with a white throat and blue breast band. They have dark blue and blackish wings with two white wing bars. Length: 5 in. Wingspan: 8 in.
Females are an unusual shade of blue-green above, with a pale supercilium and grayish wings with two white wing bars.
Seasonal change in appearance
Immatures are similar to adults, but duller.
Cerulean Warblers inhabit mature, deciduous forests.
Cerulean Warblers eat insects.
Cerulean Warblers forage rapidly, high in the tree canopy.
Forest fragmentation and cowbird parasitism are listed as reasons for the sharp decline of this species.
The Cerulean Warbler is a candidate for listing under the Endangered Species Act.
The song is a musical buzz.. A short, buzzy flight call is also given.
Black-throated Blue Warbler
Female Black-throated Blue Warblers lack two white wing bars. Female Blackburnian Warblers are browner above.
The Cerulean Warbler’s nest is a cup of bark fibers and grasses, and is lined with finer materials. It is placed on a horizontal branch, usually quite high.
Number: Usually lay 3-5 eggs.
Color: Whitish with darker markings.
Incubation and fledging:
The young hatch at about 11-12 days and fledge at about 12 days, though remaining dependent on the adults for some time.
Bent Life History of the Cerulean Warbler
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 Cerulean Warbler – the common name and sub-species reflect the nomenclature in use at the time the description was written.
DENDROICA CERULEA (Wilson)
This heavenly-blue wood warbler was first introduced to science, figured, and named by Wilson in the first volume of his American Ornithology. Only the male was figured and described from a specimen received from Charles Willson Peale and taken in eastern Pennsylvania. The female was not known until Charles Lucien Bonaparte described it in his continuation of Wilson’s American Ornithology. Strangely enough the discovery of this specimen was also made by a member of the famous Peale family, Titian Peale, the bird having been taken in the same general region, on the banks of the Schuylkill, August 1, 1825. Audubon met with it later, but was almost wholly wrong in what he wrote about it, though his plate is good.
The species is now known to occupy a rather extensive breeding range located mainly west of the Alleghenies and east of the Great Plains from southern Ontario and central New York southward to the northern parts of some of the Gulf States and Texas. It is, how. ever, decidedly local in its distribution over much of this range.
This warbler, a bird of the treetops in heavy deciduous woods, where its colors make it difficult to distinguish among the lights and shadows of the lofty foliage and against the blue sky, is well named cerulean! In his notes from central New York, Samuel F. Rathbun writes: “The type of growth to which the cerulean warbler is partial appears to be the rather open forests in the lowlands and often along some stream. During the nesting season, it will not be found to any extent in the better class of hardwood trees of the uplands; in fact, this warbler shows a strong liking for areas where large elms and soft maples and black ash are the dominant trees.” Verdi Burtch wrote to Dr. Chapman (1907) that near Branchport, N. Y., this warbler is “locally abundant in mixed growths of oak and maple with a few birch and hickory.” In other portions of its range, it is found in mixed woods of maples, beech, basswood or linden, elm, sycamore, or oaks. Frank C. Kirkwood (1901) found that, in Maryland, “the species has a decided preference for high open woods clear of underbrush. * * * The trees are principally chestnuts, with oaks, hickorys, tulip trees, etc.”
Spring: The main migration route of the cerulean warbler is through the Mississippi Valley, from the Alleghenies westward; it is rare in the Atlantic States, especially the more southern ones, and hardly more than casual in Florida and the West Indies. It enters the United States,~in Texas and Louisiana, in April, and reaches its breeding grounds in the interior early in May.
IRatlibun (MS.) says of the spring migration in central New York: “The cerulean warbler arrives in this region about the middle of May, its coming being announced by its song. With rare exceptions, it is not found in the spring migration with other warbiers and it appears to move in very small groups or singly; even in the large springtime movements of warblers known as ‘waves,’ some of the birds of which remain while others pass through the region, I have observed very few cerulean warblers. Not much time elapses after its arrival before mating takes place and nest building begins.”
Nesting: The earlier ornithologists knew nothing about the nesting habits of the cerulean warbler; Audubon’s description of its nest was entirely erroneous, and it was about 50 years after the bird was discovered that its nest was reported. This is not strange, as the nest is not easy to find and still more difficult to secure. Rathbun (MS.) writes in his notes: “During our stay in New York State, we found only three of its nests, because they were rather difficult to locate. We found the first at a height of 55 feet in a little cluster of small, twig-like branches growing on the side of a feathered elm; these clusters were close enough together to be of great use in climbing the tree, which was at least 3 feet in diameter. The nest was discovered by seeing the bird fly into the cluster. Within the next week a second nest was found by watching the female bird; it was at a height of 45 feet in a very small, fiat crotch of a soft maple. The third nest was at a height of about 30 feet.
“The nests were identical in all respects except as to shape, which varied because of its situation. Each was nicely made but not unusual in appearance. The material used was almost wholly the fine strips of the grayish bark of small weed stalks, neatly interwoven. Each was smoothly and beautifully lined with the fresh stems of ground mosses of a brownish red color, which contrasted nicely with the gray outer material. Of great interest was the smoothness with which the material was woven in.
Burtch wrote to Dr. Chapman (1907) that near Branchport, N. Y., where the bird is locally common, “the nest is usually placed on a horizontal branch or drooping branch of an elm, ranging from twentyfive to sixty feet from the ground, and from four, to fifteen, or eighteen feet from the body of the tree over an opening.”
W. F. Saunders (1900) reports eight nests found in southern Ontario; two of these were in oaks, 20 and 23 feet up, two in maples, 30 and 35 feet from the ground, and four in basswoods (lindens)~ from 17 to 50 feet above ground. He gives the measurements of three nests; they measured externally from 13/4 to 2 inches in height and 23,4 inches in diameter; internally they varied from 7/~ to 1 inch in depth and from 1~/~ to 13,4 inches in diameter. He remarks: “A feature that interested me very much was the extreme shallowness of the nests; all the other warbiers with which I am acquainted building a comparatively deep nest, and the query arises, Does the bird build a shallow nest because it places it on a substantial limb, or does it place it on a substantial limb because its nests are shallow? The attachment of the nest, also, is exceedingly frail, and I am inclined to think that few of these nests would remain in position long after the young had left.”
A nest found by Kirkwood (1901) in Baltimore County, Md., is described as follows: “The nest is made of brown bark fibre, with some fine grass stems among it, and is finished inside with a few black horse-hairs. Outside it is finished with gray shreds of bark, spider web, and a few small fragments of newspaper that had been watersoaked. * * * As the branch sloped, one part of the rim is within 5,4 of an inch of it, while the opposite part is 13,4 inches above it, the material comes down on one side of branch to 2º inches below the rim. On this side a tiny twig arches out from branch and extending to the rim is embedded in the nest, and the leaves which grew from its top shaded the nest.” The nest was 48 feet and 6 inches up from the ground and 15 feet out from the trunk of a tulip tree, with no other limb between it and the ground.
A neat little nest before me is made of materials similar to those mentioned. It is lined with the reddish brown flowering stems of mosses smoothly woven with other very fine brownish fibres into a compact rim, and it is decorated externally with various brown and gray lichens and mosses. Other nests have been reported in sycamores, beeches, rock maples, sugar maples, and white oaks.
Eggs: The cerulean warbler lays from 3 to 5 ~gs, usually 4. They are ovate to short ovate and have a slight luster. The ground color is grayish white, creamy white, or even very pale greenish white, and they are speckled, spotted or blotched with “bay,” “chestnut,” or “auburn,” intermingled with spots of “light brownish drab,” or “brownish drab.” Some eggs have spots scattered all over the surface, but usually they are concentrated at the large end, where a loose wreath is formed. Generally the eggs are finely marked, but occasionally are quite heavily blotched. The measurements of 50 eggs average 17.0 by 13.0 millimeters; the eggs showing the four extremes measure 17.9 by 13.0, 17.0 by 13.7, 16.0 by 12.4, and 17.2 by 12.0 millimeters (Harris).
Young: The period of incubation seems to be unknown, and we have no information on the care and development of the young. Incubation is said to be performed by the female alone, but both parents assist in feeding the young. After the young are out of the nest, they may be seen travelling through the woods in family parties with their parents. There seems to be no evidence that more than one brood is raised in a season.
Plumages: Ridgway (1902) describes the young cerulean warbler in nestling (juvenal) plumage as “above uniform brownish gray (deep drab gray), the pileum divided longitudinally by a broad median stripe of grayish white; sides of head (including a broad superciliary stripe) and entire under parts white; a narrow postocular stripe of deep drab gray; wings as in adults, but edgings greenish rather than bluish.”
The first winter plumage is assumed by a partial postjuvenal molt, involving the contour plumage and the wing coverts, but not the rest of the wings nor the tail. Dr. Dwight (1900) describes the young male in this plumage as “above, deep bice-green, partly concealing cinereous gray which is conspicuous on the rump and upper tail coverts, the latter and the feathers of the back often black centrally. The wing coverts with bluish cinereous gray edgings; txvo wing bands white, faintly tinged with canary-yellow. Below, white, strongly washed except on the chin, abdomen and crissum with primroseyellow, the sides and flanks streaked obscurely with dull black. Superciliary line primrose-yellow; lores and orbital regions whitish; a dusky transocular streak.”
The first nuptial plumage is acquired by a partial prenuptial molt “which involves much of the body plumage and wing coverts, but not the rest of the wings nor the tail. The grayish cerulean blue, the black streaks on the back and the white wing bands are acquired; below, the plumage is white with a narrow bluish black band on the throat and the sides distinctly streaked. Young and old become practically indistinguishable, except by the duller wings and tail of the juvenal dress.”
The adult xvinter plumage is acquired by a complete postnuptial molt in July, which he says “differs from first winter in being much bluer and whiter, the wings and tail blacker and the edgings a bluer gray. Resembles the adult nuptial, but rather grayer on the back and the throat band incomplete.” The adult nuptial plumage is acquired by a partial-prenuptial molt as in the young bird.
He says of the plumages of the female: “The plumages and moults correspond to those of the male. In juvenal plumage the edgings of the wings and tail are greener tinged than those of the male. In first winter plumage the green above is duller and the black of the back and tail coverts is lacking; below there is more yellow and the side streaks are obscure. The first nuptial plumage is acquired by a moult limited chiefly to the head and throat which become bluer and whiter respectively. Later plumages are brighter, but green always replaces the blue of the male.”
Food: No thorough study of the food of the cerulean warbler seems to have been made, but it is known to be insectivorous, foraging among the foliage, twigs, branches, and even on the trunks of trees. It is an expert fly catcher, darting out into the air for flying insects. A. H. Howell (1924) says that “examination of 4 stomachs of this species taken in Alabama showed the food to consist of Hymenoptera, beetles, weevils, and caterpillars.” Professor Aughey (1878) observed this warbler catching locusts in Nebraska.
Behavior: S. Harmsted Chubb (1919) describes the behavior of the cerulean warbler as follows:
A. bird more difficult to observe I have rarely If ever met with. His life seemed to be confined almost entirely to the tops of the tallest deciduous trees, where he would generally feed, with apparent design, on the side most remote from the would-be observer, exhibiting a wariness not expected on the part of a warbler, and finally leaving the tree, the first Intimation of his departure being a more distant song. He never remained in the same tree top more than eight or ten minutes at a time and yet rarely ventured out of hearing distance from the center of his range. Fortunately, he would sometimes take a perch on a bare twig and sing for several minutes, hut the perch was always high and generally with the sky as a poor background for observation. Had It not been for the almost incessant singing, being heard almost constantly from daybreak until nearly dark, the task of Identification would have seemed hopeless.
Voice: Aretas A. Saunders writes to me: “I have but six records of the song of this bird. There is probably more variation in the song than these records show, for all six are much alike. The song consists of four to eight notes, of even time and all mainly on one pitch, followed by a trill about a tone higher, the latter, in all of my records, pitched on C””. The first notes, in one of my records, are upward slurs, and in two others the first note of the group slurs upward, but in all of the others all of the notes are of even pitch and not slurred. The pitch varies from G”‘ to C””. The songs are undoubtedly between one and two seconds in length, but I had no stop watch at the time, so did not time them. The song is rather loud and not particularly musical. In form the song is much like that of the Blackburnian warbler, but the loudness, different quality, and lower pitch distinguish it.”
Francis H. Allen (MS.) writes the song as “wee wee wee wee heard many times without any apparent variation.” This was somewhat different from the song of a cerulean I heard, which had a “chippy” beginning that suggested the song of a yellow palm warbler, and also that of the parula warbler. Rev. J. J. Murray writes to me from Virginia: “The songs of the parula and cerulean in this section are very similar, but not difficult to distinguish. The pattern is reversed in the two; the parula’s song is ‘bzz, bzz, bzz, trill’, while that of the cerulean is a ‘trill, trill, trill, bzz’. The cerulean’s song can be expressed by the phrase ‘Just a little sneeze.'” A. D. DuBois tells me that “the beginning of the song is similar to that of the redstart, but it ends with a fine, ‘wiry,’ grasshopper-like trill, ascending in pitch and drawn out to nothing at the end.” Mr. Chubb (1919) describes two songs of the cerulean warbler as follows:
The musical exercises of the bird consisted of an alternation of two distinctly different songs, so different indeed that until the bird was caught in the act we never for a moment suspected a single authorship. One song suggested slightly that of the Magnolia Warbler but rather softer, four syllables, though not quite so well defined as In the Magnolia. The other, for want of something better, might be compared with the song of the Parula Warbler, a short buzzing triU rising In the scale, much louder and less lispy than the song of the Parula. The songs were each of about one second duration, rendered approximately eight or ten times per minute. Altogether the performance was quite musical, in aweetness far above the average warbler song. These two songs were generally alternated with clock-like regularity, though occasionally the bird preferred to dwell upon one or other of his selections for the greater part of the day.
Kirkwood (1901) says: “It also gives its song in a low tone as if it whispered it, and unless the bird is carefully watched the observer might be led to believe that he heard a second bird singing in the distance. I have watched a bird sing thus between each regular song, at other times it would not give it at all, or only occasionally, while on two or three occasions I heard it given for quite a while to the exclusion of the regular song, and qilite often have heard it given two or three or even more times in succession between regular songs.” He has heard the cerulean warbler singing through July and until the middle of August; on August 19, he heard them singing “immature or imperfect (?) songs.”
Enemies: The cerulean warbler is a rather uncommon victim of the eastern cowbird; not more than 10 cases seem to have been recorded.
Field marks: No other American wood warbler has a similar shade of heavenly blue on its back as the male cerulean; its under parts are pure white, relieved by a narrow black necklace, and it has two white wing bars. Females, young birds, and even fall males are similar, and are tinged wit.h blue above and with pale yellow below, with a whitish or yellowish line over the eye. In this plumage they resemble the young parula warbler, but the latter is much deeper yellow on the breast and has no line over the eye.
Fall: Rathbun says in his notes from central New York: “When July comes the warblers will be found quite widely dispersed in any sort of forest, because they are now moving through the country in little family groups. Now and then will be heard snatches of the spring song. This is but preparatory for their departure from the region, which takes place in the latter part of August; we have never seen this warbler after the first week in September.
Professor Cooke (1904) writes:
The cerulean warbler is a rare migrant in the States along the Atlantic coast., though It has been noted In the Carolinas, Georgia, and Florida. In northeastern Texas and Louisiana It is not uncommon. Its main route of migration seems to cross the Gulf of Mexico chiefly from Louisiana and MIssissippi. The specIes Is one of the first to start on the southward migration. By the middle of summer It has reached the Gulf coast and Is well on its way to Its winter home. At Beauvoir and Bay St. Louis, on the coast of Mississippi, It has appeared in different years on dates ranging from July 12 to 29. For a few days It Is common, attaining the height of its abundance about the first week in August. It then passes southward so rapidly that Cherrie was able to record its presence on August 24, 1890, at San Jose, Costa Rica. By November It reaches central Ecuador. Though the bulk of the birds perform their migration at this early date, some laggards remain behind until late in the season.
Dr. A. F. Skutch tells me it is “exceedingly rare in Guatemala. * * * I have never seen the cerulean warbler in Central America. In Ecuador, I found a male in the Pastaza Valley, at an altitude of about 4,000 feet, on October 15, 1939. Two days later this warbler had become fairly common in this locality, and I saw several individuals.
Winter: Says Professor Cooke (1904): “The cerulean warbler is chiefly found in winter in South America from Panamti south to Peru, in which country it seems to have its center of abundance. In western Perfi Jelski (Taczanowski, Proc. Zool. Soc. London, p. 508, 184:1′) found it common at Monterico and other places in the mountains east of Lima at 10,000 to 13,000 feet elevation, always in wandering flocks, which were sometimes quite large and contained both old and young birds.”
Range: North and South America from southern Canada to Perfi and Bolivia.
Breeding range: The cerulean warbler breeds north to southern Minnesota (Minneapolis); southern Wisconsin (Barahoo Bluffs, Madison, and Racine, possibly as far north as New London) ; central Michigan (Saginaw, Locke, and Detroit) ; southern Ontario (Thedford, Plover Mills, Warren, and Delta; perhaps Manotick) ; and southern New York (Lockport, Rochester, Ithaca, Santa Cruz Park,~ and Wappingers Creek, Dutchess County). East to southeastern New York (Dutchess County) ; rarely northeastern Maryland (Towson); southwestern Delaware (Seaford); western Virginia (Charlottes yule and Natural Bridge); western North Carolina (Morganton and Pink Beds); and northern Georgia (Lumpkin County and Atlanta). South to north-central Georgia (Atlanta) ; south-central Alabama (Autaugaville and Greensboro); northern Louisiana (Monroe and Caddo Lake) ; and northern Texas (Texarkana and Dallas). West to northeastern Texas (Dallas) ; northeastern Oklahoma (Copan) southeastern Kansas (Independence) ; eastern Nebraska (Omaha and Pilgrim lull, Dakota County); western Iowa (Sioux City); and southernï Minnesota (Minneapolis).
Winter range: The winter home of the cerulean warbler is northwestern South America, in the valleys of the Andes from central Colombia (Antioquia, Medellin, and BogotA) through Ecuador (Rio Napo, Sara-yacu, and the Pataza Valley); to southern Peri (Huachipa and Lima). It has also been found occasionally or accidentally in central northern Venezuela (Rancho Grande) ; and in western Bolivia (Nairapi and Tilotilo near La Paz). Casual in winter or migration in the Cayman Islands and western Cuba.
Migration: Late dates of spring departure are: Per6: Iluambo, March 15. Ecuador: near San Jos6, March 31. Colombia: Buena Vista, March 4. Florida: Pensacola, April 26. Texas: Austin, April 30.
Early dates of spring arrival are: Florida: Dry Tortugas Island, March 23. Alabama: Greensboro, March 26. Georgia: Atlanta, April 13. South Carolina: Clemson (College), April 21. North Carolina: Asheville, April 23. Virginia: Charlottesville, April 13. West Virginia: Wheeling, April 23. Pennsylvania: McKeesport, April 23. New York: Corning, April 25. Louisiana: Grand Isle, March 27. Arkansas: Tillar, April 6. Tennessee: Athens, April 4. Kentucky: Eubank, April 5. Illinois: Olney, April 18. Indiana: Bloomington, April 11. Michigan: Bay City, April 26. Ohio: Toledo, April 20. Ontario: Hamilton, April 25. Missouri: St. Louis, April 12. Iowa: Hillsboro, April 18. Minnesota: Faribault, April 29. Texas: Victoria, March 17. Oklahoma: Copan, March 27. Kansas: Independence, April 24.
Late dates of fall departure are: Ontario: Point Pelee, September 5. Michigan: Detroit, September 5. Ohio: Ashtabula, September 27. Indiana: Whiting, October 4. Illinois: Chicago, September 28. Kentucky: Versailles, September 4. Tennessee-Athens, September 27. Mississippi: Gulfport, September 17. Oklahoma: Copan, October 1. Texas: Austin, September 27. New York: New York, September 18. Pennsylvania: Berwyn, September 29. North Carolina: IRaleigh, September 16. Georgia: Augusta, September 16. Alabama: Birmingham, September 21. Florida: Pensacola, September 18. Costa Rica: San Jose, October 24.
Early dates of fall arrival are: Texas: Austin, July 20. Mississippi: Beauvoir, July 12. Virginia: Sweet Briar, July 20. Georgia: Athens, July 28. Florida: Pensacola, July 23. Costa Rica: Villa Quesada, August 23. Ecuador: Rfo Oyacachi, August 10. Peril: Huachipa, October 3.
Casual records: The majority of the cerulean warbiers found east of the Allegheny Mountains might be considered as casual. All records for New England should as yet be so considered, though the species has increased in eastern New York in recent years. About 10 individuals have been recorded in Massachusetts; two in Rhode Island, and one in New Hampshire. On June 2, 1924, one was collected at Whitewater Lake, in southwestern Mahitoba, the farthest north that the species has been found. There are two records for North Dakota; one near Jamestown on May 28, 1931, and another near Minot on May 24, 1937. A cerulean warbler was recorded near Denver, Colorado, on May 17, 1883, and a specimen collected on September 2, 1936, on Cherry Creek in Douglas County. A bird “observed at the Mimbres during the latter part of April” is the only record for New Mexico. On October 1,1947, a specimen was collected at the southeastern edge of the Salton Sea in California; and on October 2, 1925, a specimen was collected near La Grulla in the Sierra San Pedro Miirtir, Baja California.
Egg dates: Ontario: 3 records, June 2 to 18.
New York: 22 records, May 29 to July 9; 15 records, June 1 to 4.
Pennsylvania: 5 records, May 16 to 26.