Small rodents
Did you know that the abundance of a single prey species can determine whether the snowy owls and arctic foxes reproduce? Lemmings are the most important food source for predators, and during the so-called “lemming years”, their numbers can become incredibly high.
However, the populations of lemmings and other small rodents are strongly affected by climate changes. How? And what do these changes mean for the rest of the ecosystem?
Munching on the tundra
The Varanger Peninsula is full of small rodent specialists - that is, predators that primarily feed on small rodents.
The snowy owl and the arctic fox are considered lemming specialists, while other species also enjoy voles.
Small rodents – especially lemmings – are what we call keystone species.
They are a vital source of food for many animals, and thus also for keeping entire food chains going.
Photo: Least weasel: Jeroen van der Kooij, Rough-legged buzzard: Eeva Soininen, Snowy owl; Geir Vie, Arctic fox: Laurent Demongin og Norwegian lemming: Rolf A. Ims.
Why do we have lemming years?
When there are fewer lemmings in the tundra, the predators fare worse, and their numbers decrease.
Plants grow well in years with less grazing from lemmings.
The combination of many predators and little plant food causes the lemming populations to collapse.
The combination of few predators and a good supply of food causes the lemming population to increase.
If there are many lemmings in the tundra, the predators have more to live on, and their populations increase.
At the same time, much of the lemming food - that is, plants - is eaten up, and food becomes scarce.
What causes the lemming population to suddenly soar, then collapse and remain low for several years before increasing again?
There are many factors that affect the lemming population, and we are still not entirely sure exactly which mechanisms drive the lemming cycles.
However, research has shown that predators - especially stoats and least weasels that hunt under the snow - play an important role.
In addition, the availability of food is important for how many lemmings survive.
Ground ice: Jan Erik Knutsen, lemming: Rolf A. Ims, and arctic fox: Laurent Demongin.If you have spent a lot of time in the tundra over the years, you may have noticed that the dramatic lemming years are becoming rare?
Research suggests that the changes in small rodent populations in the tundra are due to climate changes. In the winter, small rodents live in tunnels under the snow where they dig their way to plants that they eat.
Climate changes are leading to wetter and more unstable winters. Often, a layer of ice forms on the ground covering the food for small rodents.
This particularly affects lemmings, which also reproduce under the snow, and their populations do not reach the same peaks as often as before. This can be critical for species that depend on lemmings.
DID YOU KNOW that the airport in Alta in 2011 had to establish round-the-clock lemming watch to keep the runway free of lemmings? If there were too many lemmings, they risked the runway becoming too slippery!
The picture shows a road in Kvalsund the same year, covered with lemmings. Photo: Allan Klo / NRK
What does the decline in small rodents mean for predators?
If there are fewer small rodents in the tundra, the small rodent specialists fare worse. The arctic fox and snowy owl live
almost exclusively on lemmings and end up not having offspring in years when lemming populations are low.
Other animals, such as the rough-legged buzzard and the stoat, will gladly eat voles instead of lemmings and manage well even when few lemmings are available.
The populations of grey-sided voles and tundra voles have more regular peak years and are less sensitive to climate, and easier for predators to live off.
Friends of the Plants
Lemmings and voles are herbivores, and in peak years they can remove large amounts of grass and other plants.
So, fewer small rodents should be good news for the vegetation, right?
Actually, no. Small rodents do not eat just anything, and the plants that are not eaten fare better when the plants around them disappear.
In this way, more plant species may get the opportunity to survive.
Without small rodents, some species may risk being outcompeted.
Small rodents give species that would otherwise struggle to survive a chance to thrive.
Small rodents often leave clear traces
when they have been around.
Photo: Eeva Soininen
They also leave behind a lot of good nutrients for the plants.
Photo: Eeva Soininen
Many different plant species thrive in
meadows that are grazed regularly.
Photo: Eeva Soininen
In the years between small rodent peaks, which usually occur every 4 years, grass and other forage plants have time to recover.
Small rodents are therefore important for preserving the diversity of plant species.
How we study small rodents
The life of small rodents during winter is hidden beneath the snow. Boxes with wildlife cameras give us the opportunity to monitor the activity of small rodents (voles and lemmings) and small mustelids (least weasels, stoats, and minks).
To learn about what happens to vegetation when there are fewer small rodents present, we have set up cages.
These cages are called exclosures and keep out small rodents – but also other grazing animals, like reindeer.
Exclosures make it possible to compare the plant life inside the cage with that which grows outside and is grazed.
This is not an ordinary cairn – it is a hide for one of our wildlife cameras.
Photo: Leif Einar Støvern
Here is one of our researchers busy counting plant species in an exclosure.
Photo: Hans Ivar Hortman
This is what research on small rodents used for
Knowledge about how the lemming population is affected by the climate is important for the management of the endangered arctic fox. In years with few lemmings, for example, we can put out extra food for it. Read more about the arctic fox.
Photo: COAT wildlife camera
How the small rodents fare also has an indirect impact on small game, such as the ptarmigan. Our research is used to predict the development of small game populations and improve their management. Read more about ptarmigan.
Photo: Geir Vie