OBOL:
Just in time, I hope, to help you identify those previously
undetected Alder Flycatchers that will be passing through this weekend,
I have posted a new web page detailing the differences between the
major vocalizations of Alder and Willow Flycatchers. It's at

http://www.appliedbioacoustics.com/Repertoires/Passeriformes/Tyrannidae/wiflalfl.html

Among other features, you can do side-by-side visual (spectrographic)
and aural comparison of any two of the sounds.

If the new page is too complicated, the old one is still up. One
thing it has that the new one doesn't is a longer sample of singing
by each species.

http://www.appliedbioacoustics.com/features/sounds/Traill/bird.old.html

Good birding this weekend,

Arch McCallum
Eugene