Whinfell Forest, a short drive from Penrith, is one of few red squirrel sanctuaries left in Britain, due in no small part to Miller and his team of rangers. Since 2001 they have been responsible for protecting the species in Whinfell. Red squirrels are endangered in Britain because of the bigger and more aggressive greys that arrived from north America in the late 19th century.
For four years in a row the population has stayed above target levels, and between January and September this year the rangers counted 215 reds, a 24 per cent rise on the same period last year.
The red population is also booming in other parts of the country. Vic Paine, from the Clocaenog Red Squirrels Trust in Denbighshire, confirmed that the squirrel count was up there, and a recent study found that the Isle of Wight's 3,500 reds had the right conditions to almost double in population. In Aberdeen, red squirrels were spotted in the city centre for the first time since the 1970s.
Miller believes there has been a highly unusual second breeding period this year, mostly because the reds have more food. Ecologists have recently declared 2025 a mast year, in which trees like oaks, horse chestnuts and hazels produce huge numbers of seeds and nuts to improve the likelihood of germination.
"Red squirrels are omnivorous, but during the summer and autumn they mainly eat smaller seeds like hazelnuts and pine nuts," Miller says. "Acorns and horse chestnuts tend to be too big for them. They also love eating fungi and the weather this year has been great for mushrooms too."
Robert Benson, chairman of the Penrith and District Red Squirrel Group, said that smaller shrubs like blackthorn and hawthorn had also produced an expanded number of berries that the squirrels feast on.
"Very worryingly from a conservation point of view, it has also been a huge bonus for grey squirrel breeding," said Benson. "It is particularly the oak acorns which the greys really benefit from, not the reds. Most greys are carrying squirrel pox which is lethal to the reds."
At Whinfell Forest, the grey squirrel population is controlled by a mixture of high and low tech. As well as thermal-scanning devices, GPS software is loaded into a tablet computer that lets the rangers tag a location whenever they see something notable, like a drey or a dreaded grey squirrel.
Scattered throughout the park, between the wooden Center Parcs chalets, remotely monitored trail cams are set up next to feeders where Miller thinks grey squirrels are most likely to find their way onto the site.
The holiday company encourages guests to report potential incursions but, happily, they have had zero grey sightings for more than four years. Derwentwater, 20 miles into the Lake District, was the fictional home of Squirrel Nutkin in the Beatrix Potter tale about the impertinent red squirrel, written in 1903.
Miller said that the topographical features of Whinfell made it ideal for keeping out greys. "We're kind of isolated because we are surrounded by agricultural land. It means there is limited connectivity for the greys to travel over here," he said. "There are also road barriers like the A66, and the types of trees we have here are less attractive for the greys."
Failing all else, there is a 5km "buffer zone" around the 400-acre site. It is regularly patrolled by Jerry Moss, the dedicated red squirrel ranger. Moss has a licence from Natural England to trap and humanely kill any greys he gets his hands on.
Soon, the conservation rangers hope nature will find its own way to cull the grey invaders. Several red havens around the UK have found success by reintroducing the pine marten, a small weasel-like mustelid native to Britain that preys on grey squirrels. Pine martens tend to nest on lower branches and in hollow tree trunks, but can't reach the reds, who live in dreys high up in pine trees.
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In a small camouflaged bird hide, a few metres from the cycle trail that threads through the park, Miller watched a tray of seeds and nuts, including peanuts and sunflower seeds, left out for birds as well as squirrels to provide a base of calories year-round. Typically after mast years trees will produce few to no nuts in the following cycle, potentially meaning there will be much less food in 2026.
After a few moments, a skinny juvenile red hesitantly approached the tray and began to dig in, before taking some of the nuts to bury near by. "Perhaps he thought there ought to be a tree there," joked Miller.
"Really it is a privilege to look after these red squirrels," said the ranger after the squirrel he was watching had scuttled away. "They're truly fantastic creatures and one day I'd love to see them everywhere in the UK, not just in pockets like Whinfell."