Waking Up with a Whip-poor-will

While opening mist nets this past Sunday morning at the Kiawah Island Banding Station, I was shocked to hear the song of a nearby Eastern Whip-poor-will. My first instinct was to ask one of the banding technicians near me if he was playing a recording. "Nope. You?", he responded. It wasn't me. Even though I used to have an Eastern Whip-poor-will ringtone, my phone hadn't rung, and no one else was near us. I continued to open up the nets, and again, the bird began singing from the same location. "What the heck is going on?", I asked myself. Why was this bird singing in the middle of post-breeding migration in an area where it doesn't winter?
As I pondered this non-breeding singing question, I ran into the other banding technicians who were finished opening nets. They, too, had heard the whip-poor-will. "Good. I'm not crazy or still sleeping", I sighed.
During our first net run that morning, we found the whip-poor-will in the mist net near where it was singing. This was the second Eastern Whip-poor-will caught at our banding station and by far the bird of the day.

Over the last few days, I have meditated on the question I asked myself Sunday morning when I first encountered the whip-poor-will: Why was the bird singing during its post-breeding migration?
I know that some bird species sing on their wintering grounds and even during their pre-breeding migration. But I can't recall ever reading or hearing of birds singing during their post-breeding migration.
Birds that sing outside of the breeding season may do so for one or several reasons: 1) elevated plasma testosterone levels in males cause them to continue singing, 2) to establish and defend territories on their wintering grounds, 3) to maintain social status/dominance hierarchies within the flock (for birds that flock together during migration or winter), or 4) to maintain flock cohesion.

While it is possible (isn't anything?), I am almost certain the whip-poor-will I heard will not be overwintering here on Kiawah Island, SC. Thus, it is doubtful the song I heard was intended to establish and/or defend a wintering territory.
From what I've read, whip-poor-wills form loose flocks during migration. So it is possible the song I heard may have been communicating a message of social status or presence to other flock members. (It's worth noting that we didn't catch, see, or hear any other Eastern Whip-poor-wills that morning or since then).
Perhaps the singing whip-poor-will that I and others heard was a male doing what his testosterone "instructed" him to do. A slave to his hormones.

In their book "Nightjars: A Guide to Nightjars and Related Birds", Cleere and Durney (1998) state that the Whip-poor-will (Caprimulgus vociferus) "[sings] briefly during migration".  The authors don't tell us is which migration: pre-breeding or post-breeding. Do the birds sing during both migrations?

I plan to post my observation (and question) on the relative online discussion boards and await responses. I'll keep y'all updated when I learn something new.