[Update (14th May): Not just lemmings but a plague of Scottish Field Voles. They too have benefited from increased snow cover thermal insulation and protection from predators.]
Both Norway and Sweden are reporting a population explosion of lemmings this year. This is ‘back to normal’ after a period where the absence of the legendary periodic boom in numbers of the small rodents was being blamed on climate change and had consequences for animals further up the food chain.
In 2008 a study published in Nature “Linking climate change to lemming cycles” was widely reported.
Lemmings do not hibernate, but forage under the insulating snow pack, and the depth and duration of snow cover can therefore influence their survival. When conditions are favourable they breed rapidly, reaching maturity in 20 days and producing litters of up to sixteen young in a short gestation period. Up to the mid-1990s, lemming populations typically had a cycle of three to five years in the area studied on the Hardangervidda plateau in Southern Norway.
The research reported a general warming of the area from 1990 (see Fig. 6 below)
Warmer winters resulted in increased periods of freezing and thawing such that snow froze at ground level reducing access to food. This meant that the regular explosions in lemming numbers had ceased over the past 15 years. As the Telegraph reported, their breeding habits were being disrupted literally by the “wrong type of snow.”
The last two years in Scandinavia intense winter cold and increased snow cover have provided ideal conditions for the small rodents. The Local, an English Language Newspaper in Sweden, reports:
Hordes of lemmings have been spotted leaving the safety of the mountains to make their way down to more inhabited areas, falling victim to traffic and being preyed upon by other animals.
“I must have seen a thousand just since Saturday. They are absolutely everywhere. They are swimming about in the lake close to our house, they jump on the ice floes, and they scurry around the outside of our house,“
In Norway there are reports that some areas have not seen so many lemmings since the 1970s.
In northern Norway in 1970, lemmings were so common that snowploughs were used to clear the vast numbers of squashed animals from roads. Outbreaks don’t last long: food becomes scarce, and lemmings will then often disperse en masse in search of greener pastures. On occasion, desperate to find food, they jump into water and start swimming. This behaviour led to the myth that lemmings commit suicide. [Coulson & Malo, Nature, News & Views]
Good news for foxes, owls and the many other species that will benefit from the bumper lemming year. Bad news for snowplough drivers.