The eagle owl, which can have a wingspan of up to 6ft and has powerful claws to grab its prey, has been seen in and around Blair Atholl, in Perthshire, for almost a month.
The enormous raptor is believed to have escaped from captivity as the species is not native to the UK.
It was first spotted in the area just before Christmas, according to Atholl Estate ranger Polly Freeman.
“The eagle owl is a lot bigger than any owl we have living in Britain,” she said.
“It is more like the size of an eagle. It has got huge talons and a big beak, so can be really vicious if you didn’t know how to deal with it. They are big birds, so will take other things.
“Small dogs and cats are a possibility, and they do take other birds of prey.”
The Perthshire escapee has leather thongs known as jesses around its ankles. These are used by falconers to control a bird or tie it to a perch.
“The odd one does escape,” Ms Freeman added.
“It is quite a popular falconry bird, and this one is definitely a falconry bird as it has got leather jesses on its leg. I would imagine someone wants it back, as they are quite expensive.”
As well as its great size, the eagle owl can be identified by its distinctive ear tufts and piercing orange eyes. The species was once indigenous to the UK, but fossil evidence suggests it died out around 9,000 years ago.
A few pairs are known to breed in the wild in some parts of the country, but experts believe these are all escapees or their offspring as research has shown sea crossings such as the English Channel have stopped their spread from Europe.
Eagle owls will eat a wide range of birds and mammals and are known to be intolerant of other birds of prey and owls in their territory.
There are a huge number of eagle owls in captivity in the UK, according to Keith Morton, species policy officer for conservation charity RSPB Scotland.
He said: “It is a very commonly kept bird. There must be hundreds. Nobody really knows how many because it is a completely unregulated activity.
“And given that they are carried around and not really kept in cages, their opportunity for escape is pretty high.”
The charity estimates that around 65 abscond from their owners each year, with only about half ever being recaptured.
Mr Morton says it is impossible to know how likely the Blair Atholl bird is to survive on the loose in Perthshire.
He said: “There are various risks for it, not least getting the jesses caught in things. We know that eagle owls can support themselves in the wild but we don’t know this individual’s life history so it is impossible to say what its chances are.
“Of course these birds have owners who you might suppose would want them back, so perhaps somebody will try to catch it and claim it.”
Ms Freeman added: “If it’s tame enough and hungry enough, you can tempt it in with food. And if you know what you are doing then you can catch it.
“It is not meant to be living in the wild and we don’t know how good it is at fending for itself, especially when it’s this cold.”
People have been keeping eagle owls in the UK since at least the 17th century.