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The Norwegian lemming
By: Mona Maria Solesmlie

Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Mammalia
Order: Rodentia
Suborder: Sciurognathi
Family: Muridae
Subfamily: Arvicolidae
Genus: Lemmus
Species: lemmus

Introduction:
I want to focus my paper on the population of lemmings in Norway. This is a subject with a lot of uncertainty and I find it quite fascinating. Scientists have been arguing for several years on why the lemming population size changes so radically just over a year. Only recently have they started to agree somehow on the most important factors.

General facts:
First of all I want to give you the most general facts about the Norwegian lemming. We find the lemmings in higher places in south of Norway and middle Sweden to the north and also in the north of Finland and Russia. The lemmings feed on grass, shrubs and mosses. The population of lemmings differ markedly every year. If we have an overall look, Norway houses the biggest part of the lemming population.

The lemming looks like a mouse. It is 13-15 cm long and has a stout body with thick fluffy fur. The fur is also waterproof which is essential when they live in the cold northern climate. It has long claws and small ears and tail. They live up to two years and live a solitary life, except when they group together to find new feeding areas.

The lemming is active and searching for food both day and night, usually with two hours resting periods. In the summer it burrows under tree stumps, fallen trees or rocks where it digs a small channel with grass around. In the winter they construct tunnels under the snow, where the temperature remains stabile around 1-2degrees Celsius. Here it can still search for food on the ground. In the spring, when the snow is still there, the mating season begins.

Breeding:
The lemmings are sexually mature already when they are three weeks old. The gestation period lasts for three weeks, each litter can be over ten individuals and a female can have three to five litters during a summer. These factors are also an important reason for how population size can change so fast.

Population dynamics:
The interesting thing about the lemming is that the population size differs so much from year to year. Some years we have the so-called “lemming year”, usually occurring cyclic every third to fourth year. Then density of the population is extremely high these years. Some places you we’ll have problems walking without stepping on a lemming. The funny thing is that the year after, the population size can be so small that you’ll be very lucky if you see a lemming.
Several predators and birds of prey has specialized themselves to live on the lemmings and other small rodents. These will multiply in the “lemming year”. Other preys will have a load off these years and they will reproduce a lot more these years as well. So the changing in the lemming population also affects the population size of other animals. For this reason the lemming is an important key species in the mountains.

Reasons for the changes:
The great boom and bust cycles of lemmings is what makes the species fascinating to ecologists interested in population dynamics.
The winter has a lot to say on the population size. If the temperature a winter is stabile without mild periods, most lemmings will survive the winter. There are also greater survival if we have a short winter. After a lemming year, we can usually still see a lot of lemmings following the winter. Most of the death actually happens after that!

The predators play an important role. The weasel and the snowmouse is among the biggest enemies of the lemming. Birds as owls, buzzards, gyrfalcons and gulls, and mammals such as wolves, bears, wolverines, ermines and foxes prey on the lemming as well. When the lemming population increases, it is more food for the predators and more predators survive. In the end there are so many predators that they will eat too many lemmings and the lemming population will decrease a lot. After some time the predator population will decrease and the lemming population will start to increase once more. The weasel cycle looks a lot like the lemming cycle, just a bit delayed. It is very much dependent on the lemming population cause the lemming is it’s main food source in contrast to the other predators.

One of the most important reasons is though the amount of food the lemmings can find. The lemmings eat moss instead of grass. The moss has a much longer re-growth period. So when the lemming population expands, all the moss will in the end be eaten. Now the lemmings have to travel in search of food. In these periods they travel together. On the way most of them die of hunger or they will be eaten by predators. On their search for food they follow paths and roads which often lead them through areas of human habitation. Also, a characteristic thing is that they tend to travel across rivers and oceans on their search for food. But they soon get exhausted and drown.

This behaviour has been the start of many folklore stories. The most known is that the lemming commit mass suicide. Even Walt Disney helped building up on this story. In 1958 the company made the nature documentary “White Wilderness” showing the mass suicide, which was actually staged.

An endangered species?
The Norwegian lemming is not considered an endangered species. But the last years the lemming cycle has been a bit irregular. We don’t know the reason for this though, but some people believe that the lemming is starting to be an endangered species.


Sources:
All the sources are internet addresses. You can’t find many books on lemmings, especially not here in Hungary where we don’t find the species. It was also difficult to find a real research paper on the internet

 
 
Notes (if any) by Peter Kabai: the paper found on the Internet is NOT a research article.  


 
   
 
  
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