Waterthrush Quiz: Northern or Louisiana?

I digiscoped this Waterthrush at Tower Grove Park in St. Louis Missouri on 4/21/12. Thought this particular Waterthrush would make a good quiz for those trying to learn their Louisiana and Northern Waterthrush, like me. When the Waterthrush migrate through Tower Grove Park, they are typically not singing, so you can't go by that. I am pretty sure this is a whitish Northern, but I'd like others to discuss it.