Recorded a half a dozen similar calls in the last half of March 2007. Seems about the right time for robin migration. Of course, they dominate the "dawn chorus" in my neighborhood, so cannot rule out that this was just a bird disturbed of its roost.
Closer view of same call above. No soundfile linked. Spectrogram has visual similarities to Gray-cheeked Thrush call.
American Robin recorded on 3-14-07 at 2:52 AM
Closer view of same call above. No soundfile linked.