In 1939, he was elected a Corresponding Member of the Royal Australasian Ornithologists Union He wrote A Systematic Classification for the Birds of the World (1930, revised in 1951[8] and 1960).

Between 1946 and 1966, Wetmore made annual trips to Panama to study and collect specimens of the birds of the Isthmus.

Several taxa of birds have been named in his honor, including the Cretaceous genus Alexornis and the tanagers Wetmorethraupis sterrhopteron and Buthraupis wetmorei.

Insects, mammals, amphibians, mollusks, and one plant (an Argentinian cactus), as well as a bridge in Panama and the Wetmore Glacier in the Antarctic, have also been named after him.

[11] In 1953, he married Annie Beatrice van der Biest Thielan, who became guarantor of the American Ornithologists' Union after his death in 1978.