Image: The Royal Family (left)
During his visit on May 26, 2026, the King met scientists at the Animal and Plant Health Agency’s York Biotech Campus in Sand Hutton and learned about research into an oral contraceptive for grey squirrels. Weight data gathered by the Animal and Plant Health Agency showed that a 450g threshold would exclude every red squirrel measured while admitting more than 90% of grey squirrels. Researchers are therefore developing the contraceptive and its delivery system side by side.
Grey squirrels are an introduced species that competes with red squirrels for food and living space. King Charles visited a research project in North Yorkshire exploring a new way to control Britain’s grey squirrel population and help protect its native red squirrels. The approach is designed to reduce reproduction rather than rely only on conventional population control. They also carry squirrelpox, a virus that is usually fatal to reds. Researchers are developing a targeted feeding system to deliver the contraceptive to greys while keeping red squirrels and other wildlife out. The project is part of wider research into non-lethal ways of managing grey squirrel populations. Charles, patron of the Red Squirrel Survival Trust, has championed red squirrel conservation for decades. The research programme, led by the Animal and Plant Health Agency and funded by the UK Squirrel Accord, is developing an oral immunocontraceptive vaccine. Rather than capturing animals individually, scientists hope to incorporate the treatment into bait distributed through specialised feeders, gradually lowering grey squirrel numbers. The vaccine works by preventing an animal’s immune system from producing sex hormones. Agency researchers have achieved infertility in rats fed the oral formulation, a world first for wildlife fertility control. In grey squirrels the formulation has so far produced an immune response but not infertility, and work continues to refine its potency and duration. Delivering the contraceptive only to grey squirrels is one of the project’s biggest challenges. Researchers are developing a species-selective hopper that opens only for animals above a set body weight. Trials of feeders with a weighted plate are being carried out in areas where both species live. The contraceptive is not yet a routine method of controlling grey squirrels in Britain. The project remains in research and development, with scientists still assessing how reliably it reduces fertility and whether it can be delivered without affecting other wildlife.