Conversation so far:
What did the musician Michael McDonald do with the Doobie Brothers?
Michael McDonald sang the lead vocals on some of the Doobie Brothers' best-known songs such as Real Love, Takin' It to the Streets, and What a Fool Believes.
How long did the musician Michael McDonald sing with the Doobie Brothers?
Michael McDonald is known for his distinctive, soulful voice and as a member of The Doobie Brothers from 1975 to 1982, 1987, 2019 to the present.
What instrument did the musician Michael McDonald play in the band The Doobie Brothers?
Michael McDonald played keyboards for the band The Doobie Brothers.

Question: What did he sing for the Doobie Brothers?
Self-contained rewrite: What did the musician Michael McDonald sing for the Doobie Brothers?