According to this interesting article Caledonian Crows are bigger brained than other corvids & are comparable in cognitive capacity to elephants & chimps.
http://www.nytimes.com/2011/02/01/science/01angier.html?_r=1&ref=science
http://www.nytimes.com/2011/02/01/science/01angier.html?_r=1&ref=science