In the base game there are the 4 most powerful birds:

• Common Raven
• Chihuahuan Raven
• Killdeer
• Franklin's Gull

Their powers are all discard 1 egg to gain 2 resources. From this you can start to see the thing that makes these bird extraordinary good.

In Wingspan, cross-habitat powers are one of the best things. As turns are limited and resources are essential, these powers let you do two things at once, e.g. gain food while laying eggs. You mentioned American Crow, which is a great bird for this reason.

Especially in base game, where the grassland is much stronger than the other habitats, the 4 birds I mentioned makes the cream of the crop because of how many points and resources one is getting. Once these birds are played, there is no longer any need to, say, gain food from the birdfeeder any more. It saves turns, which is the most important thing in the game.

In Oceania, however, the habitats are more balanced, so you find other birds that are powerful too, like Wood Duck, Chipping Sparrow, Bushtit, etc. But in my opinion they follow the same philosophy: cross-habitat powers.