Warbler
2 of the 7 encyclopedias on this shelf carry an entry for Warbler. Both are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
a popular name often applied to all the birds of the family Sylviidæ; (sometimes called by the French name of fauvettes); many of which, however, commonly receive other popular names as the blackcap, nightin- NEST OF REED WARBLER gale, head sparrow, red breast, redstart, stonechat, wheatear, whitethroat, etc., while many receive the name warbler warbler with some adjunct-reed warbler, etc. The more typical genera comprise birds of small size and plain plumage, usually alike in both sexes; most of them are migratory, going a long way S. of their breeding haunts to winter; for instance, the Siberian chiff chaff (Phylloscopus tristis) winters in India. Such genera are Sylvia, to which the blackcap and garden warbler belong; Locustella, of which is the grasshopper warbler (L. nævia), not infrequent in many parts of England, and found also in the S. of Scotland and in Ireland. It is found in most parts of the center and S. of Europe, at least during summer, being a bird of passage. It is of a greenishbrown color, the centers of the feathers dark brown, producing a spotted appearance; the lower parts pale brown. It is a shy bird, hiding itself in hedges and bushes, but very active, often darting out like a mouse from the bottom of the hedge, and receives its name from its chirping, grasshopper-like note.
Aiton's Encyclopedia (1910)
an American family of small woodland songsters. Some seventy species nest in the United States and Canada. There are about 155 species in the two Americas. Some idea of the diversity of color may be had from an enumeration of the colors prevailing on the backs of various species: greenish yellow, olive, olive green, bluish gray, grayish blue, blue, black, black and white, yellow, and ashy. Each describable spot of the warbler's plumage, as crown, throat, breast, wing, and tail, requires a similar and even longer list of colors for the different species, but olive colors predominate. Some warblers flit about with a quick wing in the tree-tops, snatching insects from twigs and leaves; others dash after insects on the wing like a flycatcher; others again search the bark of trees patiently like vireos and creepers. Among the noticeable species that pass northward in the springtime to summer homes in Canada are the yellow warbler with olive tinged back; the gray myrtle warbler with black sides and yellow crown; blackburnian warblers with flaming orange throat; and many others to which the best guide is a copy of Chapman's Manual and a file of Bird Lore. The volume of the latter for 1910 contains a series of colored plates invaluable to the student of this difficult family of birds.