Bull elk use bugles as a form of advertisement that escalates as cows become more active in combination with herd estrous cycles. It's a sure signal that September has arrived in elk country. Biologists theorize that the bugling helps bulls wrangle herds and, more important, intimidate lesser bulls. In short, mature bulls bugle more in an unmolested environment. Hunting pressure, weather, and herd makeup can restrain bugling, but if the cows are active and still cycling, you can expect at least some bugling. On average, cows come into heat every 21 days until they are bred. After the winter solstice, estrus becomes irregular and eventually ceases, but until then you have the opportunity to use bugles as a clue to herd whereabouts.