Hibernating wildlife: the ‘Winter Whereabouts’ of Bats and Bees!

By Kristina Wood, Terrestrial Ecologist

With limited access to food sources over the colder months, many species of wild animal have adapted different survival strategies. Here, we will look mainly at two of them, asking - where do bats and bees go during winter?

Bats

Around this time of year, UK bats enter a (hibernation-like) state known as torpor. During torpor, their body temperature and metabolism drop, allowing them to survive on stored fat reserves when food supplies are scarce. Bats prefer to spend the winter in caves, mines, tunnels, or heated buildings where the temperature and humidity will remain stable throughout the winter. Some, however, roost in trees - including clefts of branches, under tree bark, and in hollows. When it comes to UK bats, the numbers counted during hibernation surveys don’t even come close to the numbers counted during summer surveys. This means that we don’t really know where all the bats go during winter! Many assume they are roosting in our cavity walls in great numbers.

Bees

The UK is home to 24 different types of bumblebee and one domesticated honeybee. The rest (around 90%) are all solitary bees. Here’s a summary of the different ways each survive winter:

• Bumblebees: The whole colony will die at the end of each summer, except for the queen who will hide away, often in loose soil, flowerpots and within earth banks. Next spring, she will emerge to find a nesting site where she will lay eggs – having mated the previous year.
• Honeybees: During winter the (male) drone bees will die, leaving only the (female) workers and the queen. The remaining swarm crowds together tightly within the hive to form the winter cluster, with the queen at the warmest, core section of the group and the workers shaking around to maintain warmth. To sustain themselves and the heat, the cluster moves in formation around the hive to reach their reserves of honey.
• Solitary bees: Eggs are laid in cells during spring. When the grubs hatch, they remain in the cell during summer. By the end of autumn, the grubs have matured into adult bees, but rather than leave the cell, they hibernate in cocoons until the following spring – emerging for the first time at one year old!

How can we help?

Due to climate change, bats and bees are facing a hard time - often waking up during the winter period. A few warm days at the start of the year may awaken a bat or bee before their food sources have emerged, leaving them out in the cold when the temperature drops again. We can help both species by including winter-flowering plants in our gardens, building bee and insect hotels, leaving compost heaps untouched through winter, providing bat boxes, and by not disturbing bats in places that you know they are (or might be) roosting – such as tunnels, caves and even our attics!

Other critters for consideration

In addition to bats and bees, other animals also rely on natural resources to survive the harsh weather of winter. For example, the larvae of butterflies live under autumn leaves, which are also a useful nesting site for hedgehogs – alongside log piles and under compost heaps. When it comes to birds, some species will actually migrate to the UK during winter! Species such as fieldfare, redwing, and brambling can be found in dense hedgerows and woodlands, feeding on the winter fruits and berries found there.

Happy hibernating!

In the interest of best practice, NatureBureau are winding down our bat survey work for the year. Whilst it is technically permissible to carry out Preliminary Roost Assessments (PRAs) all year round, we don’t want to risk disturbing bats who may be taking up residence in attics this winter. We will likely continue PRA work until the end of November (weather dependent), so there’s still time to get a quote for the 2024 season, before Kristina goes into hibernation until April.

We do have a wintering bird survey planned, with our bird expert Paul helping a Berkshire-based charity discover which species are utilising their woodland. The surveys are part of a wider (yearlong) project aimed to advise the charity on how best to manage their woodland for wildlife. As always, please do get in touch with us if you’re considering something similar for land you own or manage.

Photo: A Natterer’s bat Myotis nattereri found in torpor between bricks in a disused railway tunnel, January 2024.