Reproduction

Breeding can occur year round. Females can breed once again within a month of giving birth. As many as 8 litters may be reared each year.

Between 5 and 13 young are born after a 2 to 3 week gestation period. They are able to produce multiple broods each year.

During a good year the Norway lemming will produce so many young that it can lead to food shortages in an area. This tends to occur once every 3-4 years.

This will cause them to undertake mass migrations to colonize new areas with more moving from the mountains down to the valleys.

Sexual maturity is reached within four weeks of being born.

Behavior

After a large breeding season the Norway lemming will undertake mass migrations before the winter sets in. During this period lemmings have become well known due to what appears to be a mass suicide event. This is caused by a number of unfortunate combinations mainly the animals winding up in unusual habitats due to their movements. Large numbers die as they try to cross rivers and lakes.

Periods of activity occur both at day and night. They tend to be active for six hours each day. In the northern parts of their range they may be exposed to days with 24 hours of daylight during summer.

When food is scarce the males will engage in bouts of boxing and wrestling.

They burrow in to hardpacked snow during winter. When this melts in the spring they must move either to higher ground or lower ground where they spend summer.

Outside of the breeding season these animals spend much of their time alone.

Predators and Threats

Natural predators of the Norway lemming include Arctic foxes, red foxes and the ermine along with birds of prey such as snowy owls and common ravens.

Their main way to avoid predation is to hide in their burrow.

In Sweden these lemmings are affected by reindeers grazing in parts of their habitat.

Climate change is thought to be a developing threat to this species going forward. A recent increase in length of time between population peaks has been attributed to climate change.

Quick facts

A common myth suggests that Norway lemmings are prone to exploding. This comes from the habit of predators moving through fields with a number of lemmings in them and killing them all. They may not eat the whole lemming leaving a body which looks like its exploded.