Maybe you can build a bird house on top of trees for the crows and they'll eat the crops surrounding the tree and in return, they'll give you gem stones by shaking the tree. Edit: The crop eating part isn't a good idea.
Instead of a bird house on top of trees, maybe something similar to the beehive? And instead of crows eating crops maybe we can do like an offering? It'll be similar to bird feed
Hmm, a crow feeding station / birdhouse... If it were to be implemented I'd suggest that basically the crow would act like a villager. You put food into the feeding station and can get credit for up to 2 gifts a week and when the crow hits the magic heart level there is a chance of it leaving some sort of bauble each time you feed it. For game purposes I'd have crows available in the winter as well if there is a crow feeding station