Current approaches to deer management are failing to control a serious and growing problem, according to new research by the University of East Anglia (UEA).
Researchers drove more than 1140 miles at night and used thermal imaging and night vision equipment to quantify the population of roe and muntjac deer in a unique study spanning the border of Norfolk and Suffolk.
The results, published today in the Journal of Wildlife Management, show for the first time that present management efforts are not enough to stop populations spreading out of control.
There are more deer in the UK than at any time since the ice age. In the absence of natural predators, populations are continuing to expand - causing a serious threat to biodiversity, as well as road traffic accidents and crop damage.
The research team investigated the numbers, sex ratio and fertility of roe and muntjac deer across 234 km2 of forested land and heathland in Breckland, East Anglia, to measure the effectiveness of deer management. It is the first time that such a landscape-scale study has been carried out in Europe and the first time that control efforts have been compared to known numbers.
They found that while deer management appeared to control numbers at a stable level, this was only because thousands of deer are 'pushed out' to the surrounding countryside each year, helping drive the further spread of deer.
In the Breckland study area, researchers identified a necessary cull of 1864 muntjac from an estimated population of 3516 (53 per cent) and 1327 roe deer out 2211 (60 per cent) just to offset productivity, with greater numbers needing to be culled if populations are to be reduced.
These figures greatly exceed previous cull recommendations for muntjac (30 per cent) and roe (20 per cent).
Lead researcher Dr Paul Dolman, from UEA's school of Environmental Sciences, said: "Deer management is often based on guesswork. This is the first time that a population has been quantified and studied in terms of how the deer are breeding - to measure the effectiveness of deer management.
Dr Kristin Wäber, who conducted the study while a PhD student at UEA, said: "Native deer are an important part of our wildlife that add beauty and excitement to the countryside, but left unchecked they threaten our woodland biodiversity. Trying to control deer without a robust
understanding of their true numbers can be like sleepwalking into disaster. To effectively reduce and stabilise the population establishing numbers is vital.
"In Thetford Forest, despite an active programme of professional management culling thousand of deer, the numbers culled did not offset productivity. It is likely that this is happening in other landscapes across much of England. This is a particular problem for non-native invasive species like muntjac.
"In recent years people have become more and more concerned about the impacts deer are having in North America, Britain and elsewhere in Europe. Increasing deer populations are a serious threat to biodiversity – particularly impacting on woodland birds such as migrant warblers and the nightingale.
"They also carry diseases such as Lymes, and if numbers are not properly managed, they can cause damage to crops as well as road traffic accidents. To help control carbon emissions the government has set targets to increase woodfuel production, but this will be hard to achieve when woodlands are under so much pressure from deer.
"Current approaches to deer management are failing to contain the problem – often because numbers are being underestimated. Cull targets are often too low. This research shows that an annual cull of 53 per cent for muntjac and 60 for roe deer is necessary to curb their continuing increase and spread."
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More information: 'Achieving Landscape-Scale Deer Management for Biodiversity Conservation: The Need to Consider Sources and Links' by K. Waber, P. Dolman (both UEA) and J. Spencer (Forestry Commission) is published in the Journal of Wildlife Management March 7, 2013.