Worth including a quick photo in brief of two grouse cocks sparring. Grouse are extremely hormonal at the moment, and they have been very noisy and conspicuous over the past few days. When I was breeding and releasing grey partridges, this was the dangerous time for cock birds as they were distracted, noisy and vulnerable to hawks. The same is true of grouse, and the more they fight amongst one another, the more likely they are to attract the wrong kind of attention.
Although this confrontation looks like a couple of blackcock at the lek, the real engagement was much faster and more fluid. These birds fanned their tails and trailed their wings through a gathering of several other cock birds before suddenly sparking into direct combat for a matter of two or three seconds. The winner was identified almost immediately and the loser was forced into open retreat on the other side of the burn.
When blackcock fight, there are periods of stylised shoving and violence, but on a properly formed lek, the result is usually feigned indifference. You might see one blackcock pursue another and engage in a kind of rolling maul, but this is more often where there are only two birds and they are prospecting on a new patch. Given that a big lek is designed to be more attractive to greyhens, it makes no sense for the dominant cock to drive away his subordinates, particularly if they can help improve his own chances of mating.