Not sure where you'd find them, but if you could find little plastic crane birds(or make some), you could make the cake look like wetlands and add the cranes.
If you want to put a picture of a crane on the cake, try searching for coloring pages crane bird, I found a few that would be easy to put on a cake.
Here's a couple I found
This one is very simple
This one would be neat, have it standing in the water, add some grass the sky, maybe a couple flying?