Life Cycle of a Bat

January

Bats spend most of the winter hibernating, a state of inactivity characterized by lower body temperature, slower breathing, and lower metabolic rate. During hibernation, bats use fat stores for fuel.

February

Bats are still hibernating, but fat stores are running low. They have little fat left to live off of now. They may leave the roost on warmer nights to find food and a drink of water.

March

If winter weather is not still severe, bats may begin to emerge and signs of limited activity can be seen. There are small numbers feeding as it gets warmer. If bad weather returns, they may become torpid (cool and inactive).

April

Bats have mainly come out of hibernation and are hungry and active, feeding on most nights. They may move between several roost sites and can become torpid again when cold. If more severe winter weather is still hanging on (which is not unusual in Colorado), bats will be slower to emerge from hibernation.

May

Bats are fully active and feeding. Females start forming maternity colonies and looking for suitable nursery sites, such as buildings or trees. Males roost on their own or in small groups.

June

Female bats usually give birth to a single pup, which they feed on their milk. Young bats are very small (less than an inch) with thin, slightly grey fur. Adult bats will catch thousands of insects each in a night.

July

Mothers continue to nurse babies. Some bats grow fast and are almost full-size; others are still very small. At around three weeks, young bats are sometimes found on the ground as they learn to fly.

August

At six weeks old, the young bats begin to catch insects for themselves and no longer need their mothers’ milk. The summer maternity colonies begin to disperse and bats may move to mating roosts.

September

Mating season begins. Males of most species use special calls to attract females, which can include purrs, clicks, and buzzing. Bats also concentrate on building up fat stores for the coming months.

October

More mating is taking place, and building up fat reserves is becoming crucial to survive the winter season. Bats are seeking suitable hibernation sites, and beginning periods of torpor.

November

Periods of torpor are lasting longer. Some begin hibernation, to save energy over the colder months, when insects are harder to find. They are using stored fat as fuel.

December

Bats are hibernating. They may roost on their own or in small groups, often in cool, quiet places like disused buildings, old trees or caves, where they hopefully won’t be disturbed.