Crows were black carrion birds associated with the forces of darkness. The most feared variety in the Westlands of Middle-earth was the large type known as crebain.
The Quenya word for "crow" is quáko, derived from Primitive Quendian k(a)wāk.
J.R.R. Tolkien, Christopher Tolkien (ed.), The War of the Jewels, "Part Four. Quendi and Eldar: Appendix D. *Kwen, Quenya, and the Elvish (especially Ñoldorin) words for 'Language'", p. 395