Английский Этимологический словарь - peck (v.)

- 13c., possibly a variant of picken (see pick (v.)), or in part from M.L.G. pekken "to peck with the beak." Pecker "penis" is from 1902. Peckerwood, Southern black for "white person" is 1929, dialectal inversion of woodpecker, taken as the type of white folks and symbolically contrasted with blackbird.