Muntjac are joining the grey squirrel and mink as the most successful foreign animals to colonise the UK.
Runner Toni Chaplin-Armer has put in a marathon effort to help the region's red squirrels as they are pushed back by the greys.
Toni, 42, competed in the London Marathon to raise over £800 for the endangered animals.
A member of the Quakers Running Club in County Durham, she completed the 26-mile course in four hours and 25 minutes.
"I couldn't have completed the race without the support and motivation of Quakers. Less than two years ago I smoked 40 cigarettes a day and could barely run for a bus. The race itself was unbelievably tough but I am honoured to have taken part in one of the greatest races in the world, the atmosphere was incredible," says Toni.
The donation will go to Save Our Squirrels, a three-year project run by the Northumberland Wildlife Trust.
Toni first became involved with the charity via her role as operations manager at Eshott Hall Estate in Eshott, Northumberland.
The estate runs training courses for local farmers and landowners on how to control grey squirrels, and manage habitats to benefit the red squirrel.
"Red squirrels are a vital part of our cultural heritage and native fauna but are under serious threat from greys," says Toni.