Scottish Bat Life cycles

Bats are highly adapted animals, with unique life cycles. Scotland’s seasons shape everything our bats do, from winter survival to busy summer activity.

Winter

Winter is all about surviving the cold and making it to spring.

Winter is the quietest period for bats. Insects are scarce, so they save energy by entering long periods of torpor. Their heart rate, breathing, and body temperature fall to very low levels to help them survive until spring. Winter roosts are usually cool, sheltered spaces such as tree cavities, stone buildings, and cellars with stable temperatures and humidity.

Roosts used in winter are called hibernacula, and it’s important not to disturb winter roosts. Waking from torpor comes at a significant energetic cost for bats, and can impact their chances of surviving until spring.

Mild spells when insects are flying can bring brief bursts of activity, which is normal and not usually a cause for concern!

Spring

In spring, bats wake up and begin feeding, moving to intermediate roosts on their way to their summer homes.

As temperatures rise, bats wake more frequently and begin feeding more regularly to rebuild their energy reserves. Females prepare for pregnancy after storing sperm in the autumn, and make their way towards their summer maternity roosts.

Early sightings often involve bats feeding along hedgerows, woodland edges, parks, and gardens. You may spot bats for the first time each year during April or May, especially on calm evenings.

Early summer

Early summer is all about new babies.

After a short pregnancy, females gather in warm, safe maternity roosts where they each give birth to a single pup. These roosts are usually warmed by the sun or manmade features and are essential for successful breeding. Young bats grow quickly and begin to fly within just a few weeks.

During this period, it is especially important not to disturb roosts or flying bats. Unexpected noise, lighting changes, or building work can cause unnecessary stress to nursing mothers with only a short period of time to raise their young.

Late summer

This year’s young bats begin feeding independently.

This is when bats are most visible, and people may notice more evening activity than at any other time of year. This year’s young and the adults are all feeding and preparing for winter at this time of year. This is a critical period in determining whether young bats survive their first winter.

Autumn

It’s breeding season!

During autumn, youngsters often stay in their maternity roosts while the adult females move to breeding roosts. Males will attract harems of female bats by ‘song flighting’, and successful males can share their roosts with large numbers of females. The female bats do not become pregnant right away, instead storing semen over winter and having a short pregnancy the following spring.

At the end of autumn, bats begin returning to their preferred hibernacula, often returning to the same locations year after year for decades.

Why the life cycle matters

Scotland’s bat species rely on different types of roosts throughout the year. Each stage comes with its own sensitivities, and different roosts have different levels of significance for each bat. Understanding this helps people recognise why bats and their roosts are protected and why expert advice is needed before carrying out work on buildings, trees, or other structures.

Small changes in weather patterns can affect feeding opportunities and winter survival, making awareness even more important!

References

Bat Conservation Trust 2023. The Bat Life Cycle. Bat Conservation Trust, London.
NatureScot 2020. Bats: Licensing and Guidance. NatureScot, Inverness.
Scottish Government 2019. Wildlife Crime and Protected Species. Scottish Government, Edinburgh.