The pine marten would, of course, eat any kind of squirrel given the chance, but the reds appear to be better at avoiding this native predator than their grey rivals.
Since their arrival from North America in the 1800s, the bigger greys have driven out the reds from much of the UK. Scotland is now one of the reds’ last bastions with about three-quarters of the total British population.
It seems counter-intuitive that increasing the numbers of a predator could help one of its prey species, but it is another example of the importance of individual species to the health of an eco-system, in this case making it more resistant to a non-native invasive species.
This was famously demonstrated by the extraordinary “ecological cascade” of effects following the reintroduction of wolves to Yellowstone National Park. It raises the question about how many more species could be reintroduced to the benefit of the natural world.