A lattice of grit sites should be established across the moor, either marked with small posts or the grid reference of each heap recorded with a handheld GPS. The spacing will be dependent on spring grouse densities with the aim of providing one box per pair. A density of 50 pairs of grouse per 100ha would therefore require 50 boxes spaced every 150 metres. With densities of grouse currently well in excess of this, box density should be much higher, with some moors having a grit box every 75 metres.
Grit boxes in this photograph are marked by posts at intervals of 100 metres.
Conducting grouse counts in July and spring are vital to give estimates of autumn/spring densities. This, together with the number of grouse harvested and an allowance for natural mortality, allows the numbers of grit sites required to be calculated. Grit boxes should be placed in short vegetation, with proximity to standing and running water avoided.
With the recent occurrence of Cryptosporidium baileyi in grouse, the siting and density of grit boxes is more important than ever. Grouse transmit the infective stages of crypto (oocysts) via mucous expelled from their nasal cavities and in both the fibrous and caecal dropping from grouse, so preventing contamination of grit boxes with grouse faecal material is essential. Boxes no larger than 20x15cm should be used, with numerous small drainage holes in the base. Raising boxes slightly off the floor will aid drainage. Preventing the boxes holding moisture is essential because crypto oocysts require moisture for survival in the environment. Placing stones around the grit boxes will help to make them more obvious to grouse. Once a gritting pattern has been established and the grouse are using it, only move boxes 2-3 metres annually to help prevent a build-up of crypto oocysts.
Medicated grit should be placed out on the established gritting sites in early spring and withdrawn at the end of June. By providing a limited period of access to the grit, this will help offset resistance build-up in the worms to the anthelmintic.
Grit box hygiene
No more than 500g of grit should be placed in each box. A grouse consumes approximately 35g of grit per month, therefore 500g will last a pair of grouse approximately seven months. Some sites may be more popular and require replenishing. All grouse faecal material should be removed from boxes on a regular basis. Fresh medicated grit should be used each year. All old medicated grit should be removed from the boxes in late June/early July and removed from the moor.
Do not place new medicated grit on the top of old medicated grit. This will not only dilute the effectiveness of the anthelmintic but may increase infection from crypto. The development of grit boxes more like poultry pellet dispensers may be worth considering to prevent faecal contamination of the medicated grit.
When medicated grit has been withdrawn from the moor, plain quartz grit should be made available to the birds. Because no drugs are incorporated this can be placed on the ground 3-5 metres away from the medicated site to provide “clean” ground for the birds. Again, only a small quantity should be placed at each location so it is used up by the time that medicated grit is provided to the birds again.
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✓ History of disease
✓ History of control
✓ Medicated grit
✓ Assessing grouse for worms
✓ Deployment of medicated grit and grit box hygiene
✓ Best practice checklist