I also looked for a while and had little luck. I did find though that the brain-to-body-mass ratios for two of the smartest known species of birds -- the Western Scrub Jay, and the New Caledonian Crow -- are comparable to those of the chimps. These two species have shown very sophisticated cognition.
Blast.
I'll have to keep the question in mind for the next time I run into a neuroscientist.
ITT we talk about whatever.