Wilson's plan was materialized in 1808 through the publication of the first volume of what we might call America's first guide to birds called American Ornithology or the Natural History of the Birds of the United States.
This pioneering work (unlike the catalogs and lists of birds that had previously been written on American birds) focused on species in the deciduous forests of the eastern United States, described the behavior and habitats of birds and with illustrations that he himself performed. It was the first American ornithological book to describe and illustrate birds.
The work was accomplished between 1808 and 1814 and comprised 9 volumes. Wilson lived up until the seventh volume and the last two were continued by Bonaparte and George Ord.
The Cerulean Warbler was collected and described by Wilson in the second volume of American Ornithology in 1810 under the scientific name Sylvia cœrulea.
The bird described was a male, he said that it had the habits of a flycatcher –possibly due to its foraging style when it seems to catch insects in the air- but that due to the shape of its bill it should be considered a warbler (Wilson, 1810).
He described it as one of the rare species in Pennsylvania, assumed it was migratory since he saw it in summer but not winter and added that the latest date he had observed it was August 20th, when it was retreating south early. The collected specimen (No.7309) was kept in the Peale Museum, in Philadelphia, Pennsylvania.
Wilson, A. (1810). Cerulean Warbler [Engraving], American Ornithology Vol. II.
The female was described in 1825 by Charles Lucien Bonaparte, a prominent French naturalist and nephew of Napoleon, who continued Wilson's work after his death in 1813.
It was a specimen collected on the banks of the Schuylkill River (eastern Pennsylvania) that was foraging in an oak tree, at first they thought they had a male with summer plumage, but upon dissecting it he determined it was a female (Bonaparte, 1828).
With both sexes already collected, Bonaparte describes that the major difference between them is that the female is greenish rather than blue, lacking dark streaks on the back and showing a yellowish tinge on the undersides.
Bonaparte, C. L. (1828). Female Cerulean Warbler [Engraving], American Ornithology Vol. II.
Bonaparte, C. L. (1828). American Ornithology: or the natural history of birds inhabiting the United States, not given by Wilson Vol. II.
Wilson, A. (1810). American ornithology or, The natural history of the birds of the United States Vol. II.