I found this story in the UK's Daily Mail:
"Mutant 'testosterone-fuelled' Russian black squirrels in Cambridgeshire are giving their grey cousins a taste of their own medicine and driving them from their homes.
A Cambridge academic believes the unusual black squirrel now makes up half of the total squirrel population in the area from which they have originated.
The upstarts are the genetic mutations of grey squirrels. And although nuts may be their food of choice there have been reports of their hungry Russian counterparts savaging stray dogs.
<snip>
"Three years ago, a pack of Russian black squirrels bit to death a stray dog in a Russian park. They were said to have scampered off at the sight of humans, some carrying pieces of flesh."