Would a life-bearing Earth-like world with 3g average gravity produce more or fewer flying creatures than Earth?
On one hand, heavier gravity would make flying more difficult, owing to greater weight restrictions on the flying creatures' bodies.
On the other hand, the greater density of the atmosphere on our 3g world might provide more support for a flying creature--especially small ones.
Let's assume that our 3G world is the same distance from its sun-like star as Earth is from the sun, and that its orbit is no more eccentric than Earth's.
Also, could our 3g world affect that nature of its flying creatures? For example, might not some of the small animals on this world evolve bladder-like structures that they could inflate with air and in which they could warm the air, allowing them to function like little hot-air biological blimps.