Slatestarcodex has a great post on the intelligence of birds.1
The big take-away: due do the weight restriction of flight, birds have been under huge evolutionary pressure to miniaturize their neurons. The result?
Driven by the need to stay light enough to fly, birds have scaled down their neurons to a level unmatched by any other group. Elephants have about 7,000 neurons per mg of brain tissue. Humans have about 25,000. Birds have up to 200,000. That means a small crow can have the same number of neurons as a pretty big monkey.
Bird brains are 10x more computationally dense than our own? This is a big deal. To put this in perspective, if you replaced just 10% of your brain volume with crow neurons you could double your computational capacity.
I know this sounds like complete insanity, but given how every intervention to raise IQ has been ineffective, this bird-brain scheme is probably much more promising than any pharmaceutical based approach.
This raises all sorts of interesting questions. How does miniaturization effect heat dissipation? Oxygenation? Energy consumption? Could one build a human-sized brain with bird-dense neurons?
Though the brain is immunologically privileged, there is still the neuroimmune system. Can we genetically modify crow cortical neuron progenitor cells to not trigger the neuroimmune system? Is there any chance of human neurons and bird-neurons integrating usefully?
Brain grafts have been unpromising for intelligence enhancement because you would have to replace much of the brain to make a difference. With bird tissue, this problem is 10x less relevant.
Or more ominously, what if we breed crows for brain size? Hyper-Intelligent flightless crows pecking keyboards in hedgefund basements? To paraphrase Douglas Adams, there is another theory which states that this is already happening.