Lousiana Waterthrush; May Migration through Northern Illinois

Is this a Northern or Louisiana Waterthrush?
Espenscheid Forest Preserve, Rockford, IL; 5/1/2011.

When I took the photo of the waterthrush (Above), I wasn't sure what type of warbler it was. After researching and identifying it as a waterthrush, I wasn't sure what type of waterthrush it was - the Louisiana Waterthrush or the the more common Northern Waterthrush.  Now I have seen a Northern Waterthrush before (in Mexico last winter) as it had more yellow on its belly than the Louisiana, so I concluded that it must be a Louisiana, but as I read further, I found that Northern's can also have a white breast and belly beneath the brown streaking. So then I had to check its other identifying marks: the Louisiana has a slightly larger bill and a slightly more broad white eyebrow than the Northern. Again being a novice at bird identification, unless I saw them side by side, I don't think I could make a definite identification. So then I had to resort to listening to its song. When I went to a couple of bird sights on the Internet ( http://www.whatbird.com/ and http://www.allaboutbirds.org/ ) to listen to each of their songs, I knew what I took a picture of was a Louisiana Waterthrush, because its song is what I was hearing while hiking through Espenscheid Forest Preserve.

A Louisiana Waterthrush, Espenscheid Forest Preserve, Rockford, IL; 5/1/2011.

As luck would have it, I caught two different Louisiana Waterthrushes on digital film the same day, but in two different parts of the Preserve (Above).  Louisianas will spend their summers by forested streams and wooded swamps of the eastern half of the U.S. - south to Lousiana (of course), Mississippi, Alabama, and Georgia, but north of the Gulf Coast, and northward to central Wisconsin, Michigan, New York, New Hampshire and Vermont.