[thaumasiotes]

Intelligence is not a metric that the concept of efficiency can be applied to. To evaluate efficiency, you need a benefit and a cost. "Intelligence" is just one thing; the most you can do is evaluate it in terms of more or less.

What kind of intelligence efficiency do you want? Most efficient use of time? Glucose? Volume? Mass? Highest utilization rate? Are we looking at computational capacity? Computational quality? Economy in computational demands?

> Bird bones are shaped optimally to put the bone where the most stress is.

That is true, but it doesn't distinguish bird bones from the bones of any other species. However, bird bones are uniquely bad at suffering that stress.

> I recall reading once that they were hollow.

Also true. They also have very low density in what you might consider the non-hollow parts. That's why they function so poorly for maintaining physical integrity.

Sometimes two goals are in conflict. Birds need bones to maintain their physical integrity, but in order to fly, they have trouble supporting bones. The fact that their bones are subject to more constraints than those of other vertebrates doesn't mean that they magically have better bones than other vertebrates do. It means they have worse bones, because the quality of their bones had to be subordinated to their unique need to fly.