Deer (roe and red) are a valuable wildlife and sporting asset and should be a long-term component of Scottish moorland. Deer are of concern to moor managers whose primary interest in continued moorland investment is the production of a harvestable surplus of red grouse, an activity associated with an important range of environmental goods. In this habitat deer densities should be maintained but at levels that allow sheep tick to be controlled so as to protect investment in moorland conservation.
Background
The GWCT does not conduct research specific to deer population control. Our position is largely structured around our research into tick control, which is our most relevant work with deer as a component part. Our research suggests that:
- Deer are the likely driver behind the UK’s increasing tick population (Scharlemann et al 2008).
- Tick burdens are rising on grouse (Kirby et al 2004) with consequently lower chick survival through biting and louping-ill transmission.
- Louping-ill virus (LIV) is always a key factor explaining variation in grouse population performance (Smith et al 2000) and is a well-known issue for vets as it affects sheep health.
- Initial monitoring on moors in Strathspey and through the Angus Glens Moorland Health Project suggests deer densities lower than 5 deer per 100ha are more than likely sustainable, as sheep treated with acaricides (aka ‘sheep-mops’) remain effective in reducing tick abundance. Our data suggests that higher deer densities can render sheep-mop management of tick ineffective, especially where sheep are thinly distributed on the ground.
- However, we are still researching the questions of how many deer and hares are too many and how many sheep are enough as regards effectively controlling disease in red grouse. This work is under way on a number of moors across Scotland.
Management
The GWCT does not conduct deer-specific research, so when advising on integrated deer and grouse management we use best practice and expert opinion. Following on from our position:
- Moorland habitats in good condition for red grouse benefit from light, well-distributed deer browsing; the sporting value of a property is usually enhanced by a well-managed stalking population; deer dung may be valuable for invertebrates; and deer carcasses can be locally important food for protected species such as eagles.
- Sheep and mountain hares are integral parts of many Scottish moors, and a key part of both habitat and disease management. Deer management plans must consider the role of sheep, hares and muirburn as moorland components, both of which are researched and advised on by the GWCT.
- Where deer have been historically present moors should not maintain zero deer densities.
- Intensive short-term suppression of deer populations may be necessary for disease control where tick are very abundant and LIV levels very high, in order to allow often ‘sheep-mop’ based strategies for grouse to gain traction and drive investment in moorland management.
- Suppressed deer numbers should be released as soon as possible and sustainable levels maintained, which requires monitoring of grouse and moorland condition.
- Sustainable deer densities for tick control are often also typically thought to be similar to those linked with sustainable grazing patterns on heather and scrub woodland habitats, and with maintaining linkage of deer populations.
- Deer management, especially to very low levels, has consequences for neighbouring deer forests; collaborative management is important and should be addressed before decisions are taken on how to achieve the targets.
- At this time we do not believe free-ranging deer can be effectively or safely treated with acaricides to kill ticks using current tools.
- Suppression of deer populations may be achieved by culling, regular disturbance, sacrificial habitats or fencing.
As regards fencing particularly:
- Fencing can allow properties to manage deer and sheep (as regards farming, grazing and tick management) on individual units. However for many fences should be a last resort as fences represent a collision risk to grouse, a cost burden for estates, may impair deer welfare if poorly sited, can require updating of sheep management practice and may be unsightly.
- If fencing is required preferred locations are where fencelines have historically existed and can be reinstated.
- To mitigate visual and impact issues electricified stock fencing should be considered as a first alternative, then full height deer fence. In both cases the fence should be marked with anti-collision strips in line with best practice guidance.
Dr. Adam Smith
Director Scotland
May 2013 (updated July 2014)
References
- Scharlemann, J.P.W., Johnson, P.J., Smith, A.A., Macdonald, D.W. & Randolph, S.E. 2008. Trends in ixodid tick abundance and distribution in Great Britain. Medical and Veterinary Entomology, 22: 238-247.
- Kirby, A.D., Smith, A.A., Benton, T.G. & Hudson, P.J. 2004. Rising burden of immature sheep ticks (Ixodes ricinus) on red grouse (Lagopus lagopus scoticus) chicks in the Scottish uplands. Medical and Veterinary Entomology, 18: 67-70.
- Smith, A.A., Redpath, S.M. & Campbell, S.T. (2000). The Influence of Moorland Management on Grouse and their Predators. Her Majesty's Stationery Office, Norwich.