A female snowy owl was spotted over a week ago at the RSPB's Balranald Reserve on North Uist, and on Saturday a male also turned up, about five miles away at Grenitote.

Ornithologists now hope the pair will get together and become the first snowy owls to breed in the UK for more than 30 years. The last time was in Shetland in 1975.

Small numbers of the spectacular birds show up from time to time in the Western Isles, but have not bred as far as is known. In February last year, two birds were spotted, but they were both males.

Martin Scott, the Western Isles officer with RSPB Scotland, said: "This is great news. These birds are an absolutely spectacular sight and an inspiration to anyone that's lucky enough to see them. Just to have snowy owls around is special enough, but to have the prospect of them breeding is even better."

He added: "They are five to six miles apart, but they do move around to hunt over quite large areas, so there is a good chance they might bump into each other.

"Hopefully, they are compatible and settle down, which would be a huge coup for the islands.

"There has been a snowy owl seen in Uist since 2003, which we think is a male, and the fact that a female has turned up at this time of year is just right, as they will both be looking for mates."

The birds, among the largest owls in Europe, stand almost 2ft tall with a wingspan of over 5ft. They would normally be found around Arctic Norway or Russia at this time of year.

Mr Scott said: "They should be up in the Arctic Circle, but they are obviously getting plenty of food. There are lots of rabbits about, so it's all set up perfectly for them."

It is thought the male is a Canadian bird which was blown off course during a storm in the Atlantic. It is unclear whether the female is from North America or Europe.

Mr Scott added: "They can get blown off course and then get stuck on the wrong side of the Atlantic as it is difficult for them to get the energy up to fly against the prevailing wind back across. Lewis is probably a bit warmer just now than they are used to, but hopefully it will be OK for them."

The species is known to millions of JK Rowling followers because Harry Potter has a pet snowy owl, Hedwig.

It is one of a number of species that go through cycles, with periodic "irruptions" – a spreading out of their territory in response to food being more widely available. It is thought the arrivals in the Western Isles could be related to an increase in the number of lemmings, the snowy owl's favoured prey, in the Arctic Circle.

Until 1975, snowy owls did breed for a number of years near Fetlar in Shetland.

In 2003, a snowy owl set up home around Traigh Ear, north of the Balranald nature reserve, and attracted bird-watchers from Glasgow, Edinburgh and Inverness.

Two years later there were sightings in Shetland, Wester Ross and Aberdeenshire.

In 2006, a number of the birds were spotted in the Western Isles, but it is not thought they bred.