Brownback

In the fall and winter I shot in the lagoons and in the harbor of Greytown blue-wing and green-wing teal and gadwalls; also sickle-bill curlews, peeps or least sandpipers, and brownbacks or grass birds.

Source: wiktionary

Two "brownbacks," as they are known on Cape Cod where these came from, are shown in Figure 36. The one whose head is held forward represents the male in fall plumage — the back slate gray and the breast a cinnamon pink.

Source: wiktionary

The color work on the postage stamps will not be new to the bureau. In addition to the work which it has done on proprietary stamps, it has mixed and used every shade of color in its other work. Brown was used on the “brownbacks,” green on the "greenbacks;" different blues on customs stamps and on the backs of bonds.

Source: wiktionary

Of course the printers are not all doing the same kind of work: some are printing the greenbacks, some the brownbacks, some the faces, and others the backs and faces, of the revenue stamps.

Source: wiktionary