This unusual bird's head is the removable cover of a vessel, most likely a hu or a zun, that would have been in the shape of a standing bird. A bird-form zun, in the Freer Gallery of Art, is illustrated by G.W. Weber, The Ornaments of Late Chou Bronzes, Rutgers University Press, 1973, pp. 348-55, no. 64, pl. 74. Also illustrated, pp. 356-59, no. 65, pl. 75, is a vessel in the form of a crouching griffon or chimera, with separate cover in the form of a bird's head, which may be a replacement, in the collection of the National Palace Museum, Taipei. Both of these vessels are dated first quarter of the 5th century BC.