Well..... you already know where they're not! That's half the battle.
I don't think I've ever killed a bird in the same spots I've seen them hang out in the winter..... but I have killed them close by.
In Central New York State, they tend to spend the winter in pine because of the deep snow. The snow isn't as deep and some food can be found. Then as the snow melts they start traveling into area's that get a lot of sun to take advantage of mother natures food chain.
As the ground warms from the suns rays, the snow melts, insects and small creatures (lizards, frogs and such) get active and small plants start to grow before anything in the deep woods so I would start in any area of good sun exposure with roosting trees and clean water near by.
I like to check out old corn fields and old alfalfa fields on a southern facing slope, especially if their winter holding area is near.
Give that a try and let us know what you find.