British red deer could face the same fate as red squirrels

A study of deer on Scottish estates found invasive sika deer increased while native red deer declined, and researchers warn this pattern could mirror past losses of red squirrels.

Researchers report that invasive sika deer are increasing while native red deer populations are falling in parts of Britain. The sika, introduced from east Asia in the 19th century, are described in the study as more fertile, more tolerant of poor conditions, and better able to maintain condition on the same feed. The study, published in Ecological Solutions and Evidence, analysed deer on estates in Scotland and reported a 10% rise in sika and a 22% decline in red deer for 2024–25. Key findings: - Analysis on Scottish estates found sika numbers rose by 10% in 2024–25 while red deer numbers fell by 22%. - Authors and land managers reported that sika display higher fertility, broader diet tolerance, and greater resilience to poorer habitats and weather. - Researchers note current culling often does not distinguish species and may not be reducing sika populations effectively. - Experts warned that sika–red hybrids could carry traits that further challenge native red deer. Summary: The study suggests native red deer may face sustained declines where sika gain a toehold, and authors draw parallels with earlier losses of red squirrels. Undetermined at this time.