A genetic investigation is underway in Denmark to determine whether sika deer, recently classified as an invasive species by the EU, have crossbred with native red deer. Blood and muscle samples are being collected from hunted sika deer across the country to test for hybridization, a concern that prompted the EU classification but which many experts believe is unfounded in Danish conditions.
Collecting Samples from Hunted Deer
Veterinarian Flemming Thune-Stephensen sticks a needle into a fresh wound and fills it with blood. With a knife, he cuts off a small piece of meat to take with him. Behind him lie two dead sika deer with blank eyes, shot shortly before.
The blood sample will be used for chromosome studies, while DNA from the muscle sample will reveal whether there are unexpected genetic strains in the sika deer. Thune-Stephensen collects samples for a genetic mapping project investigating whether two deer species have interbred, as some fear may be the case.
Debate Over Invasive Species Classification
At the end of 2025, the debate surrounding sika deer in Danish nature took a turn when the Danish Agency for Green Land Conversion and Water Environment announced that the animals would henceforth be considered an invasive species to be eradicated throughout the EU.
Many viewed this as an unfortunate decision, including officials responsible for managing the old deer park in Marselisborg forest near Aarhus. The park houses many sika deer alongside fallow deer, wild boar, ducks, and other animals.
Sika deer are not naturally native to Europe. They come from Asia, and therefore some believe there is a risk they could breed with red deer and create hybrid populations that would damage the native deer population. However, others argue that the risk of breeding between two different species like sika and red deer is only theoretical and minimal at best.
Physical Barriers to Crossbreeding
At the Danish Hunters Association, Niels Søndergaard, head of wildlife management, called the decision “out of proportion” and “overkill” when not a single case of species crossbreeding has been seen in the more than 125 years the animals have lived side by side in Danish nature.
Flemming Thune-Stephensen explains that the average weight of a red deer hind is 80 to 120 kilos, while a red deer stag weighs 140 to 180 kilos. This size difference creates practical barriers to crossbreeding. If a red deer stag attempted to mount a sika hind, she simply could not bear his weight and would collapse, making mating impossible. Similarly, a sika stag trying to mount a red deer hind would be unable to reach.
Minister Softens Culling Requirements
In late December, Minister for Green Tripartite Jeppe Bruus announced that the new EU rules would be implemented as leniently as possible. This meant that although sika deer are unwanted, they would not be shot when living in deer parks. Even in the wild, there would be no active culling campaign.
In other words, they would be allowed to die naturally of old age and disease. However, the minister’s statement did not explain how it would be ensured that they do not escape or breed.
Scientific Investigation Launched
In early January 2026, it was decided that genetic studies would be conducted. The Danish Forest Association initiated the investigation, with veterinarian Astrid Ingstrup from Store Merløse serving as project leader alongside Niels Tommerup, a professor of genetics at the University of Copenhagen.
Results are expected in a couple of months. The Danish Forest Association has around 650 members, primarily private forest owners, including Count Bendt Tido Hannibal Wedell, Denmark’s largest private landowner through his company Wefri.
Citizen Proposal Demands Better Evidence
A citizen proposal titled “Postpone the decision that sika deer in Denmark should be eradicated” has gathered significant support. The proposal, co-sponsored by Wedell and initiated by Thune-Stephensen, argues that the decision to eradicate sika deer was made on a very thin scientific basis.
The proposal contends that experiences from England, Scotland, and Ireland have been uncritically transferred to Danish conditions. Red deer on the British Isles are considerably smaller than Danish red deer, meaning the physical prerequisites for mating between sika and red deer exist there, which is why hybridization occurs. However, hybridization has never been observed in Denmark.
Additionally, sika deer in Denmark have 66 chromosome pairs while red deer have 68. Therefore, any potential mating between the two species would likely not result in viable or fertile offspring.
Hope for Danish Exemption
If no crossbreeding has occurred in Denmark, the Danish Forest Association hopes the country can apply for an exemption from the EU rule. The association points to the process involving mink, which also landed on an EU list of unwanted species in 2025.
Denmark voted against that classification, and the Environmental Protection Agency subsequently stated that Denmark would fight for a special arrangement for Danish mink farmers. A similar approach could potentially be applied to Denmark‘s sika deer population.
The chairman of the Danish Hunters Association expressed support for the investigation, stating that creating more knowledge in this area can only be beneficial. As research continues, the fate of Denmark’s approximately 1,000 sika deer remains uncertain, pending scientific evidence that could challenge the EU’s invasive species classification.
Sources and References
The Danish Dream: Denmark issues formal apology to Greenland spiral victims
The Danish Dream: Best Gartners in Denmark for Foreigners
TV2: Prøver skal afsløre om invasiv art har parret sig med de forkerte
