One important bit to remember is that because birds have a different brain area (the pallium) with stack structure similar to what we mammals have in cortical stacks, the relationship between brain volume and potential intelligence is no longer the same: the cortex, which is where we have our cortical stacks, is a thin layer on top of everything else, so it's surface-area dependent; the pallium is solid and it seems it can be a varying proportion of the rest of the brain.

So... birds descend from dinosaurs, and this means we can't make assumptions about how intelligent those critters were.

OTOH, they were around for a few million years, and there have been no artifacts found that show they used tools.

Back to corvids. We have a lake place in NW Maine. Ravens are commonplace. I've made a point of watching them. When one finds a good bit of food (roadkill) they land, inspect, then fly away - a bit later they come back with quite a few more ravens.