Why culled deer carcasses in Scotland should be left to rot, according to experts

Hundreds of thousands of kilos of vital nutrients are removed every year when deer carcasses are lifted off the hill, ecologists have said.

In Scotland, deer populations have been actively managed since 1959, primarily to control over browsing. Currently, all four wild deer species present in Scotland - red deer, roe deer, fallow deer and sika deer - are considered overabundant.

In a new report, ecologists have said removing the carcasses from the land after a cull, however, could be undermining habitat restoration - and that they should be left to decay naturally.

Researchers at The University of Edinburgh and Yale University in the US quantified annual nutrient losses from the removal of deer carcasses. They estimated that 251,188 kg of calcium, 195,652 kg of nitrogen and 152,834 kg of phosphorus are lost across Scotland each year.

Kristy Ferraro, PhD candidate at Yale School of the Environment and lead author of the research, said: “We show that the prevalent practice of removing deer carcasses comes at a cost to ecosystems by depleting essential nutrients, which could have widespread implications for ecosystem recovery.”

Of the three nutrients the study looked at, the loss of calcium was seen as having the biggest environmental impact, with deer culling stripping the land of more calcium than sheep farming. The researchers said low calcium soils can hinder both commercial and native woodland regeneration and can also impact birds, which experience declines in shell thickness in low calcium environments.

The landscapes within Scotland are already considered nutrient poor, which can limit plant growth in important habitats like regenerating woodlands. In parts of the country, this is treated with fertilisers.

Aside from recycling nutrients, carcasses bring other ecosystem benefits, such as being a food source for small predators and have been shown to distract predators away from the nests of ground nesting birds, researchers said.

They suggested deer carcasses should be left where they fell, taking public access, waterways and livestock into consideration.

An alternative solution proposed was to reduce the number of mass culls and allow deer to die naturally on the landscape. Ms Ferrero said one way to do this would be the reintroduction of natural predators.

The researchers collected cull data on deer from 2010 – 2022, using data provided by NatureScot and environmental data from Space Intelligence for the study. They then combined cull numbers with the average mass of each deer species and estimated the phosphorus, nitrogen, and calcium present in these.

They said their findings are only estimates and that they couldn’t directly evaluate how removing deer carcasses affects ecosystems. Future experiments analysing carcass decomposition and environmental features would be needed for this.

Tom Turnbull, chairman of the Association of Deer Management Groups (ADMG), which has been running for more than three decades, said the group would be “extremely concerned” to see the practice of leaving carcasses on the hill as being “normalised”, regardless of whether certain science might support this.

“It is Interesting to note also that in the case of domestic livestock, a dead animal must be retrieved and disposed of properly and not left on the hill due to the risk of spread of disease,” he said.

Referring to the Wild Deer Best Practice Guidance, Mr Turnbull said the carcass can be left if it is dangerous to reach, or where the deer is diseased or seriously emaciated. However, in such situations Best Practice Guidance is that the animal should be gralloched - disembowelled - and checked for disease and buried. 

But he said there are “significant” arguments as to why carcasses should not be left, which include public concern, pollution of water, and sensitivity to seeing dead, decaying deer.