Well folks, I figured out my avian mystery from my nocturnal atlasing last weekend at Aquasco Farm Park, when I made another attempt this morning.
I heard the same call after the sun rose and walked across the field directly at the source. And it was a yellow-breasted chat just issuing one strange note. And that led me to an area with a fledgling bird in half fledgling feathers, and half adult feathers.
Good news is the pre-dawn visit yielded a barred owl fledgling too. Yay for fledgling season.
Thanks to all you helpful, thoughtful, and kind collaborators for your ideas.
Best,
Denise Ryan