No arrests have been made, and little is known about the attackers. Most underground rooster fighting operations are independently operated — not by local gangs or Mexican drug cartels, Trevino said.

Cockfighting is illegal in Texas, but the rooster battles remain common along the Texas-Mexico border, Trevino said. La Blanca is about 15 miles north of the border.

The cockfighting operation uncovered as a result of the ambush featured several rings with bleachers, a concession stand, a rooster weighing room and tournament brackets that tracked the best birds, Trevino said.

"Cockfighting is a big problem in South Texas - not only in Hidalgo County but in all of South Texas," the sheriff said. "To them it's a sport, but to the state of Texas, it's a crime."

(Editing by Dan Burns and Vicki Allen)