When John James Audubon arrived in Liverpool in July 1826 Traill helped him to find a publisher for his The Birds of America. Audubon named the Traill's flycatcher after him, which at one time referred to a species which included both the willow flycatcher (Empidonax traillii) and the alder flycatcher (Empidonax alnorum).
Edinburgh University and the Encyclopædia Britannica
Traill returned to Edinburgh University in 1833 as a professor of medical jurisprudence. He edited the 8th edition of the Encyclopædia Britannica (1852–61), which concluded a year before his death.