Thread: Unprompted bout of roaring in Reds

Occasionally I hear a stag going off for no apparent reason. It seems to be at any time of the day. The most recent I heard was late morning. Roaring 2-3 times a minute over a 20-30 minute period, and seemingly oblivious to any responses from stags (or us) from a distance. Then the stags appear to switch back into normal mode and becomes just as cagey as before, with barely a peep out of them.
Does anyone have any ideas as to what might be triggering this behaviour ?