Removing culled deer carcasses in Scotland may be draining environments of nutrients
The removal of deer carcasses after deer culls in Scotland, primarily done to prevent overgrazing, is removing hundreds of thousands of kilos of vital nutrients from the environment every year, potentially undermining habitat recovery. This is according to new research published in the British Ecological Society journal, Ecological Solutions and Evidence.
A new study by researchers at The University of Edinburgh and Yale University quantified annual nutrient losses from the removal of deer carcasses by utilising nationwide Scottish cull reports. The researchers estimate 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, Ph.D candidate at Yale School of the Environment and lead author of the research said: “Our study quantifies an important yet overlooked aspect of current deer management in Scotland. 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. Low calcium soils can hinder both commercial and native woodland regeneration and can also have knock on effects for 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. To combat this, much of Scotland receives fertilizer treatments.
Aside from recycling nutrients, carcasses bring other ecosystem benefits, such as being a food source for small predators like pine martens. Carcasses have also been shown to distract predators away from the nests of ground nesting birds, like capercaillies, during the breeding season.
Co-author, Chris Hirst, a Ph.D candidate from the University of Edinburgh, said: “The results of our study call for deer managers to reconsider current practices and integrate approaches that retain a proportion of deer carcasses within ecosystems. While we specifically look at nutrients and do not assess other environmental impacts of carcasses or make a value judgment on deer culling, our findings will help guide evidence-based recommendations for deer and nutrient management to better protect Scotland’s plans for large-scale ecosystem recovery and sustainable wildlife management.”
The researchers suggest two solutions for retaining nutrients from deer carcasses in the environment. The first is for culled deer carcasses to be left where they fell. “Of course, this raises practical questions about where is suitable to leave carcasses” said Ferrero. “We have to consider public access to the area and keeping carcasses away from livestock and waterways. Despite this, there are numerous areas of open-range and dense woodlands in Scotland which could serve as initial implementation sites.”
An alternative solution is to reduce the number of culls and allow deer to die naturally on the landscape. One way to do this while still managing deer numbers is the reintroduction of natural predators. Ferrero said, “Through predation, both the consumed carcass and what is left behind would ultimately remain in the ecosystem. Further, due to the way in which predators hunt, they would also create heterogeneity in carcass distribution on the landscape, creating hotspots of nutrients that would be difficult for human-hunting to replicate.”
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.
To quantify the amount of nutrients that deer culls and carcass removal are extracting from Scottish environments, the researchers collected cull data on red, roe, fallow, and sika deer from 2010 – 2022, using data provided by NatureScot and environmental data from Space Intelligence. They then combined cull numbers with the average mass of each deer species and estimated the phosphorus, nitrogen, and calcium present in these.
The researchers warn that their findings are only estimates and that they couldn’t directly evaluate how removing deer carcasses affects ecosystems. Future experiments analyzing carcass decomposition and environmental features would be needed for this.
Ferrero added that “Our estimates probably underestimate the actual nutrient losses because the official records of deer culling in Scotland don’t include every instance of deer being killed or every deer death. For example, several thousand deer are killed each year in vehicle collisions.”
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