It seems ridiculous to be carting bags of grit around the hill for the grouse when there is such an abundance of natural stone fragments already on offer. Struggling up a particularly steep slope yesterday with a 25Kg bag of stone on my back, I noticed a thick smear of granite grit which had been exposed by running water at my feet. The little stones were almost exactly the same size and quality as the quartz I had on my back, and there was clear evidence that grouse were using them – there was shit and feathers in the deep old cart tracks.
Up on the hill, I found that my old grit boxes are being used again after being freshened up a few days ago, but the new line of twenty four boxes has had no grouse interaction whatsoever. I had to query my own sanity at hauling mounds of tiny stones onto the hill when it was already abundant and accessible, but this was the same conundrum when I first started to grit this hill. I despaired after a fortnight because the grouse appeared to totally ignore my hard work, but they soon came round and were using the piles keenly within a couple of months.
It’s hard for we humans to understand the value of grit since we have no biological equivalent. We can assume that it’s an optional extra for grouse; a kind of “nice if you can get it” luxury; and so it’s inevitable that we under-rate its value. Stories from wind farm development sites describe grouse coming keenly to the new hardcore roads to get grit while the diggers are still working on them, and the impression is almost of birds falling on the stones with something like ravenous hunger – they may have struggled to access a reliable supply of grit for generations, and populations often boom in the years immediately following development.
Grouse simply cannot survive without grit to grind up their rough, coarse diet, and experiments undertaken during Lord Lovat’s Grouse Enquiry showed that birds quickly ail and die without a steady supply of little stones to “chew” their food. Most birds will scratch together enough grit to satisfy their needs, but grouse are able to control and regulate their grit intake according to climate and environment. They take on more in the winter when times are hard and every calorie is valuable and less in summer – an experiment at Leadhills in the 1960s showed that the amount of grit in a grouse’s gizzard can be a hundred times greater in winter than summer. Even more intriguingly, grouse can control the amount of grit they excrete, saving it up when grit is in short supply and then casting it en masse when it is worn down, for example after snow when it may not have been possible to replace it.
I want my grouse to prosper, not scratch together just enough to survive, but the grit piles should also help to form the foundations for territories in the spring. The grouse may well be using natural grit on the hill, but while this resource is hugely abundant, it is only located in a few small areas across the hill. Birds from the wet, grit-less back hill are forced to travel some distance in order to stock up – in my experience, this gritting takes place at dawn and dusk, just on the edge of darkness. This is probably a response to predators, and I’m aware that every time they fly across open ground, they expose themselves to attack. If they have everything they need in the security of the high tops and the deep moss, that can only improve their chances.