Coues' Gadwall or Washington Island Gadwall (Anas strepera couesi) is an extinct dabbling duck which is only known by two immature specimens from the Pacific island of Teraina (formerly known as Washington Island), Line Islands, Kiribati. They are in the National Museum of Natural History in Washington, D.C.. The bird was named in honor of Elliott Coues.
A male and a female are known, which resemble the immature appearance of the Common Gadwall except for the black bill with a higher number of fuiltering lamellae, black feet, and the much inferior size (which may be due to the birds not being fully grown). The male resembles a male Common Gadwall in eclipse plumage save for some white speckling on the breast and back. The female looks like a small Common Gadwall female; the primary wing coverts were not patterned black, and the inner web of the secondary remiges was grey instead of white.
Measurements are: wing, 199 mm; bill, 37 mm; tarsus 36 mm. This means the birds were the size of a Cape Teal or Garganey, with a total length of 40-45 cm. As the birds were not fully adult when shot, it is not clear whether they would not have grown a bit larger.
The status of this bird is controversial. While many scientists consider it as dwarfed subspecies of the Common Gadwall (Anas strepera strepera) others argue that the two individuals might have been just juveniles of a local breeding population that might not even be taxonomically distinct. The Common Gadwall is a known vagrant to the Tuamotu Islands and Hawaiʻi for example, which are about the same distance from the species' breeding grounds as is Teraina (which moreover lies in between these two groups). This makes it entirely possible that the Washington Island gadwalls were just the offspring of a few vagrant Common Gadwalls, maybe settling after being wounded by hunters. On the other hand, Streets' reports suggest that there was a population of these ducks of some size present, and thus they may have lived there since quite some time and indeed be worthy of recognition as a distinct taxon.
The first of two published observations of the Washington Island Gadwall took place in January 1874, and it was first described by Thomas Hale Streets (1847–1925) in 1876. Streets reported about the two immatures he shot and which were found in a peat bog.
The cause of its extinction might be the extensive hunting by settlers of Tabuaeran (Fanning Island) which have shot large numbers of migrant ducks on both Teraina and Tabuaeran each year. W.G. Anderson, a local resident stated in 1926 that growing up on Teraina and Tabueran around the turn of the century, he had never encountered a native population of gadwalls on Teraina. Thus, the population's disappearance can be fixed to the last quarter of the 19th century, between the mid-1870s and 1900.