The resurgent population of pine martens that is returning to Powys may be helping reduce the area's grey squirrel population.

Research has shown that while both red and grey squirrels are on the pine martens' menu, it is the greys, the non-native species which has become by far the more prominent in the UK in recent years, that really whet the animals' appetite.

The study by Queen’s University Belfast, published in Mammalian Biology and funded by UK wildlife charity People’s Trust for Endangered Species (PTES), also shows that pine martens gobble down grey squirrels exclusively in spring and summer, during the squirrels’ breeding season.

As such, it is now thought pine martens may raid grey squirrel nests (known as ‘dreys’), specifically targeting juveniles and females caring for young - which may go some way towards explaining a fall in the number of greys in Ireland and Britain.

In 2019 the pine marten had returned to the woodlands of Mid Wales, thanks to a pioneering project to restore the native mammal to a region in which it once thrived.

Between 2015 and 2017, more than 50 martens were brought from the Highlands in Scotland to the forests of the Cambrian Mountains where they were on the brink of extinction.

This new research, led by Dr. Joshua Twining from the School of Biological Sciences at Queen’s University Belfast, also showed that pine martens do feed on native red squirrels, but at a much lower level.

Red squirrels have adapted to live alongside pine martens as both species evolved in Europe, and have a greater awareness of the threat posed by the predators.

Grey squirrels may also provide pine martens with more energy, so are larger and are found in higher numbers than red squirrels.

Dr. Joshua P. Twining, from the School of Biological Sciences at Queen’s University Belfast, adds: “Our findings align with the evolutionary physiology and morphology of many small carnivores - slim and slender, pine martens are adapted to pursue prey into small ‘hidey holes’, such as dreys, that other predators cannot access.

"With semi-retractable claws, and extremely flexible joints which can turn almost 180 degrees, pine martens have evolved to climb.

"Although such adaptations make pine martens less efficient at chasing down prey, being the only arboreal predator in Great Britain and Ireland gives them easy access to the refuges of squirrels high up in trees.

"Our results are interesting as they help explain the mechanism underpinning how pine martens are able to regulate invasive grey squirrel populations, and give a much-needed boost for another one of its prey species, our native red squirrels.

"This magnificent yet mysterious member of the mustelid family is native to Britain and was once one of the most abundant predators in the country.

"Now, after centuries of widespread persecution and habitat loss, most recent estimates suggest there are only around 3,000 in Ireland and 9,000 in Great Britain, with only approximately 100 thought to be living in England. Just last week, pine martens were listed as ‘Critically Endangered’ on the Red List for England’s mammals."