I suspect the more significant difference here is the selection pressures. Take a good look at any part of a bird and you'll see millions of years of selection for reduced weight. The cost of weight is just so much greater when you're flying. Interesting too that bats tend to have lower neuron counts than say rodents. Did dinosaurs have a more weight efficient brain before flight, or were they forced to shrink before re-evolving that complexity in a smaller package?