Until recent years, sightings of the owl in Norway were extremely rare.
The 113 nests counted so far this represents a remarkable turnaround on the fortunes of the bird, according to a report by broadcaster NRK.
Trond Berg, a nature film maker with the broadcaster and member of Birdlife Norway in the Elverum area of Hedmark, said that the high number of nests was “extreme”.
The great grey owl, which is considered a endangered species, is native to taiga areas of Russia, Scandinavia and North America.
Sightings of it in Norway are rare and, until 1989, were restricted to the far northeastern Finnmark county, before sporadic appearances in Hedmark began to create a sensation amongst birdwatchers.
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“When we observed three nests in Elverum in 2010 it was big news. But now things have completely taken off,” Berg told NRK.
The number of sightings is related to prevalence of mice, the main prey of the birds – good years for mice are also good years for the owls, he said.
Great grey owl in flight. Photo: mzphoto/Depositphotos
“We have seen before that when rodent numbers peak, we see increased numbers of great grey owl nests. But this year's figures smash all previous records,” the film maker added.
The bird has now been observed in 13 of Hedmark's 22 municipalities, according to NRK's report.
Half of those sightings were in the Elvedal area.
Berg said that researchers were still trying to find out why the area had become such a popular choice for the owl.
“It's a mystery. And why has it not happened before now? There have been almost no nests here, probably for hundreds of years. Something new is happening in nature and that's what makes this so special,” he told NRK.
The film maker also said that the low numbers of mice in 2015 and 2016 made the high amount of sightings even more surprising.
“We hope, believe and guess that 2018 will be a super mouse year. Only the gods know how things will go for the [owl] nests then,” he said.