Scotland is being colonised by escaped German beavers after the £2million official reintroduction of the animals proved a flop.
A new report from environment chiefs shows a group of rogue Bavarian beavers, which most likely broke free from captivity, are thriving.
It comes after recent study suggested the Norwegian specimens imported to Argyll under an official government trial would most likely not survive without outside help because their young were dying.
Beavers were hunted to extinction in Scotland 500 years ago but in 2006 a mysterious group of the animals was discovered in Tayside.
Genetic tests showed the escaped animals were from Germany, most likely Bavaria.
A new report from Scottish Natural Heritage (SNH) says the rogue beavers have been found to be “well adapted to living in Scotland”.
One of the largest species of rodent, the creatures can weigh up to 30kg (66lbs).
About 150 of them were found to be living on the River Tay – and the only ill-effects they seem to have suffered were most likely caused by fighting.
The SNH report states: “All live-trapped animals were physically healthy, presented no obvious deformities, external parasites, discharge or obvious signs of disease.
“Two individuals had evidence of previous, healed wounds (on tail), indicative of beaver-inflicted injuries, most probably as a result of former territorial disputes, which is common and to be expected in this species.”
In 2012 the Scottish Government decided to allow the Tayside beavers to stay while they carried out an official reintroduction programme 100 miles away in Knapdale, Argyll.
The Government beavers were flown from Norway and placed in quarantine in Devon before travelling to Scotland to be released.
However, the results of the five-year trial showed only one or two of the 14 kits, or baby beavers, born in the wild survived.
In addition, only half of the 16 adult beavers could be accounted for. Three of the males had died, while five of more of the animals were recorded as “missing”.
A report on the programme concluded that the mortality levels for kits meant the beavers would not be able to establish a self-sustaining population.