Why Is Turkey Serve During Thanksgiving Day?

I've heard several answers... the one I beleive most is simple... there was a painting showing a family sitting around a big feast and the mom was setting the turkey out on the table, and the family looked so happy that everyone wanted a turkey for that coming thanksgiving (i can't remember what the year was and i think the artist was norman rockwel, but i could be pulling the name out from something else) and the turkey has been a symbol since then... but the indians and pilgrims DID eat turkey... and deer... and fish... and whatever else they had handy.