At the Battle of the Little Bighorn, the Sioux and Cheyenne war chiefs used a variety of methods to command their men. John Siverston noted the Indians' use of eagle horns: "We could not see the Indians, but they were signaling all the time to each other with their little bone whistles." The Indians used other audible signals as well. Charles DeRudio recalled, "we heard the powerful voice of a savage crying out, making the same sound four times, and after these two signals, we saw 200 or more savages leave the bluffs and ford the river, evidently leaving the ground."

Great article at source

Thanks for finding this - I like reading anything to do with any kind of history - looking forward to reading the source article later.