Cornell’s Merlin App has identified this as a King Rail, a member of the Rallidae Family, along with other Rails, Gallinules, and Coots.

Both the handsome adult and the distinctive all-black chick were new to me. I watched them for ten minutes and the adult kept this posture, perhaps a cooling mechanism on a hot August day, while the chick tottered around in the grass.

Donnelley Wildlife Management Area, Green Pond, SC
August 8, 2021