During their pioneering research work on Hawaii which last 23 years, Olson and James found and described the remains of 50 extinct bird species new to science, including the Nēnē-nui, the Moa-nalos, the apteribises, or the Grallistrix "stilt-owls". In 1982 he discovered subfossil bones of the long ignored Brace's Emerald on the Bahamas which gave evidence that this hummingbird is a valid and distinct species. In November 1999 Olson became notable for his open letter to the National Geographic Society where he criticised Christopher P. Sloan's claims about the dinosaur-to-bird transition which referred to the fake species Archaeoraptor. In 2000 he helped to resolve the mystery of Necropsar leguati from the World Museum Liverpool which turned out to be an albinistic specimen of the Grey Trembler.
