 (Zink 1996, Zink & Weckstein 2003)

Thick-billed fox sparrows are almost identical in plumage to slate-colored fox sparrows but have a more extensive blue-gray hood and a less rusty tail.The most striking feature of this bird is its enormous beak which can appear to be three times as large as that of the markedly small-billed slate-colored fox sparrows.A thick-billed fox sparrow's beak also differs in color from that of the slate-colored.