Today we saw this while in Gairloch and, speaking with locals, found that it's common practice this time of year.
The idea is to burn away all the old, matted heather, allowing the new growth to come through unhindered. Evidently new heather is much better for wildlife to eat and it looks better too - "more purple". It's also much safer to set fire to it now when it won't spread so fast than allow summer wildfires to get going.
"Muir" is the Scots word for "moorland" - hence "muirburning" and is the origin of the surnames Muir and Moore.You learn new things each day.
Just while I'm on - here's the view from the same place that the photo above was take, but in the opposite direction. That's Strath beach and in the distance is the Torridon range of mountains.