By Emma Brennand
Earth News reporter
The owls rotate their bodies to face the sun
Snowy owls use their white feathers to reflect sunlight, warning rivals of their presence, scientists say.
The reflective feathers create a blindingly bright warning beacon that can be seen over long distances.
Owls with the whitest plumage showed the brightest signals, often signalling from perches on the ground where they use the light reflected from snow to enhance the glare.
The findings are published in the International Journal of Avian Science.
Researchers from the University of Saskatchewan, Canada, and the Museum of Natural Sciences (CSIC) in Spain, observed the colour and behaviour of snowy owls (Bubo scandiacus) over ten winters.
Despite their evocative name, the colour of the owls' feathers can vary from brown to pure white, depending on their age and sex.
When fully mature, the birds are predominantly white - a colour perfectly suited to their snow covered habitat.
The team found that the brightest areas of plumage were always found on a bird's face, throat and breast.
The owls orientated these birght white areas to face the sun.
"Their lack of spots and the high reflectance of the face are indicative of enhancement for signalling," explained lead researcher Gary Bortolotti.
"And [we think] plumage colour variation influences the size of the signal."
The owls' plumage can vary from pure white to brown
White is an ideal signalling colour because, since it reflects light so effectively, it can be seen from long distances.
Researchers believe that many birds use their plumage as a visible signal to defend their territory.
And this study suggests that a snowy owl's bright white feathers are a very effective signal, allowing it to make its presence known over large areas of its very open habitat.
The team monitored the colouration, orientation and height of the perched birds at a number of wintering sites.
They saw that the snowy owls would rotate their bodies towards the sun, and follow it over the course of the day.
This "solar orientation" is believed to optimise the strength of their territorial signal.
"The birds constantly shift throughout the day, and even change the height of their perch depending on the sun," Dr Bortolotti told BBC News.
He explained that "heavily spotted" birds preferred to signal from high perches, such as electricty poles.
"But the white birds, which are predominately male, and the older birds, actually signalled from the ground," he said.
The team suspect that the low-perching birds were taking advantage of the reflection of light off the snow, which is known as albedo.
"What surprised me was that the birds were looking directly into the sun across a flat snow covered landscape," said Dr Bortolotti.
"To be human and do this is literally painful on the eyes."
Snowy owls have adapted "eyelashes", which are made up of long bristles and other feathers which help to reduce glare.
The study supports previous research that colour and patterns of plumage play an important role in visual communication between birds.