Gyrfalcon numbers rise sharply in northeastern Iceland

Gyrfalcon numbers in northeastern Iceland have increased by about a third since last year, according to mbl.is, which reported on a survey by the Icelandic Institute of Natural History. The institute counted 35 occupied territories in a 5,300-square-kilometre research area containing 88 known gyrfalcon territories.

The increase is described in a report on research by ecologist Ólafur K. Nielsen, who has studied the gyrfalcon population for many years. The report puts the year-on-year increase at 40 percent, after 2025 saw the lowest level of territory occupancy since monitoring began.

The population has declined in recent years, partly because gyrfalcons have been severely affected by avian flu, which now appears to be receding. Ptarmigan are the gyrfalcon’s main food source, and the size of the gyrfalcon population has generally followed changes in the ptarmigan population. That pattern appears to have changed while avian flu was at its most widespread.

The outbreak began in the British Isles in 2020 and reached Iceland with migratory birds in spring 2021. Between early 2021 and March 2026, 26 gyrfalcons were tested for avian flu. All had been found dead or dying, and 14 tested positive. The first confirmed infection in a gyrfalcon was found in late July 2021 and the last in late September 2025. No infected wild birds have been found in Iceland since March 2026.

Much of the population’s growth was driven by one-year-old birds. Seven of the 29 territorial gyrfalcons aged in spring 2026 were one year old, or just under a quarter of the total. The report says it is unusual for birds that young to establish territories.

The high proportion of young territorial birds may reflect improved survival among juvenile birds over recent winters, as well as the large number of vacant territories. Similar developments have been observed among gyrfalcons in the British Isles and mainland Europe as populations begin recovering after avian flu outbreaks.

Young birds fledged from 12 gyrfalcon pairs. However, productivity, measured as the average number of young per occupied territory, was below average despite abundant ptarmigan and favourable weather during the breeding season. The report suggests that this may be because many breeding birds were inexperienced newcomers that had not previously attempted to breed.

Ptarmigan surveys in northeastern Iceland found the largest breeding population recorded since research began in 1981. The surveys counted 14.1 males per square kilometre. According to the report, a larger ptarmigan population in the region may not have existed for more than 70 years.

Monitoring also found that eggs had been taken from one gyrfalcon nest and that a monitoring camera at the nest had been removed. Signs suggested that another nest may also have been interfered with.

“Such behaviour is completely unacceptable, especially given that the gyrfalcon has been protected for decades and that its population has declined significantly in recent years,” the report says.