Wildlife experts at the University of Aberdeen, who carried out the research, have also raised fears over the potential impact spiralling stoat numbers could have on Orkney’s £14.2 million nature tourism industry by depriving visitors of interesting species to watch.
The report recommends “rapid and decisive intervention” to avoid any further spread of the stoats, which are predicted to cause long-term damage to the local ecosystem.
Stoats are opportunistic predators and will attack rabbits, rodents, game birds, waders, chicks and eggs. They have been shown to eat hen harrier chicks.
The first stoats were spotted in Orkney just five years ago, but the latest figures show 380 ‘reliable’ sightings.
They have been established in Shetland since the 17th century, but numbers remain moderate to low and with no major impact on local species. This is thought to be due to the lack of equivalent species to the Orkney vole.
The report concludes that measures are required in Orkney to “reduce or remove” the population.
SNH has now set up a technical advisory group made up of experienced SNH staff, academics and conservation specialists to tackle the stoat problem.
“Orkney is fortunate to have such a diverse and high-quality landscape and natural heritage,” said SNH’s Graham Neville.
“Arable land complements cliff colonies and the seas around Orkney are teeming with life and marine plants. That makes it plain we have a duty to conserve its nature.
“The report tells us it is highly likely that invasive, non-native stoats will change the ecology of Orkney.
“That will have a heavy impact on its place as a home for birds of prey and other species.
“This is a significant issue with implications for the affected species of Orkney.”
But he warned that ridding Orkney of stoats would not be easy or cheap as the latest distribution figures are “conservative”.
He added: “We estimate that in reality the majority of mainland and connected islands will be occupied by stoats now or in the very near future.”
A cull has not been ruled out but the agency has given assurances that “handling of stoats will be carried out with the individual animal’s welfare as a priority”, with support from bodies including the Scottish SPCA.