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 quite 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 with 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 José, 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 Panamá south to Perú, in which country it seems to have its center of abundance. In western Perú Jelski (Taczanowski, Proc. Zool. Soc. London, p. 508, 1847) 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.”
DISTRIBUTION
Range.—North and South America from southern Canada to Perú and Bolivia.