neuroscience - Do smaller intelligent animals have a higher neuron density to account for their seeming intelligence? Otherwise, what?

It seems like there's a lot of very small animals that have a much higher intelligence than what you would expect if you linearly projected intelligence as a function of brain size. There's ravens, crows and parrots which are much smaller than humans but have a recognizably high intelligence and emotional capacity. Then there's rats and general rodents like squirrels or similar animals like raccoons, and I guess an octopus to throw in which are good at problem solving and fierce fighters. Then there's also bugs like ants which are somehow very versatile and can adapt to many situations despite being that tiny, and with recent information may also have a recognizable emotional capacity like possibly bees.

It would make sense to me if the correlation between neuron density and intelligence isn't linear, but I don't have the information to make any determinations.