Endangered red squirrel populations in the UK have dropped dramatically—from around 3.5 million to less than 300,000. This decline is especially severe in England, where estimates suggest only between 15,000 and 39,000 red squirrels remain, even in protected areas like Formby on Merseyside. Grey squirrels, which were introduced from North America in the 19th century, have outcompeted red squirrels for food and habitat and are responsible for spreading a deadly disease called squirrel pox. This disease causes severe ulcers and blindness in red squirrels, often leading to their death. Grey squirrels were first brought to the UK around 150 years ago when Thomas V. Brocklehurst, a Victorian banker, reportedly released a pair into Henbury Park in Cheshire after returning from the United States. Today, there are an estimated 2.5 to 2.7 million grey squirrels in the UK, according to Graham Paskett from the Red Squirrel Survival Trust. Jackie Foott, from the British Red Squirrel conservation group, explained that red and grey squirrels cannot coexist in the same area. She said, "To protect the reds, you have to get rid of the greys—we realized that a while ago." Grey squirrels are considered invasive, non-native pests that cause at least £40 million in annual damage to forests and forestry services. The inability of red and grey squirrels to coexist is due to several factors. Grey squirrels are more efficient at finding food and shelter, and they carry squirrel pox, which is fatal to red squirrels. Currently, there is no fertility control method that targets grey squirrels without affecting other species, and gene therapy is still at least a decade away. For now, lethal control—shooting or trapping—is the only method available to reduce grey squirrel numbers and protect red squirrels. Paskett, however, believes a new method could be available within five years. The Red Squirrel Survival Trust is funding a field trial by the government's Animal and Plant Health Agency to test an oral contraceptive for grey squirrels. The trial will use a "hopper" device that allows grey squirrels to access the contraceptive, as they are larger and stronger than red squirrels. If successful, landowners and forest rangers could adopt this method to help control grey squirrel populations. Another potential solution involves the reintroduction of pine martens, a native predator that evolved alongside red squirrels. Pine martens eat grey squirrels, which are less cautious around them, while red squirrels can detect and avoid them. Foott noted that while the exact origin of grey squirrels in the UK is uncertain, they were introduced largely for aesthetic reasons. Today, conservationists work with landowners and farmers to manage grey squirrel populations near red squirrel colonies. The UK government has acknowledged the threat posed by non-native grey squirrels and is taking steps to protect the endangered red squirrel population.