Swainson's Warbler fledgling call

This is recent audio of a Swainson's Warbler fledgling at Howell Woods Environmental Center in North Carolina. I was at first drawn towards a chipping adult and then heard an unfamiliar sound coming from nearby vegetation. Approaching the sound, I observed a young Swainson's Warbler on the ground, so recently out of the nest that it couldn't fly.
(early June, NC)