The booming ground is a lek: a patch of low or grazed prairie where males hold small adjacent territories and display through spring mornings. Birds stamp their feet rapidly, raise the elongated neck feathers called pinnae into horns, spread the tail, and inflate bare orange air sacs on either side of the neck.
The resulting boom is a low, hollow, three-syllable note. Low frequencies carry through open country with little attenuation, and the sound is commonly reported audible a kilometre or more away. Females visit, watch, and mate with a small number of favoured central males, so mating success on a lek is heavily skewed.
Site fidelity is the vulnerable part. Leks are traditional, and when a booming ground is ploughed or built over the birds do not simply relocate reliably. That, plus the loss of most native tallgrass prairie, explains why isolated populations have become small enough to suffer inbreeding effects.