Help needed with bird ID

["Ed Anson" ed_anson]

I have been hearing this bird in my neighborhood for some time now, but 
I haven't been able to identify it. Whenever I hear it, it's completely 
hidden by the trees, so I have no idea what it looks like.

I have posted a brief clip from a recording at
http://home.comcast.net/~edanson/DawnChorus.mp3

This is very early in the dawn chorus, in my suburban neighborhood 
about twenty miles north of Boston, four minutes or so past the start 
of twilight. Very little is heard, until the call of the locomotis 
commuterensis is answered by my mystery bird. He calls a few times and 
then remains silent for awhile.

This call is in none of my identification CDs, but I bet someone in 
this group will recognize him immediately.

Ed