The big sleep
05 December, 2013
As the cold weather closes in, some of Historic Scotland’s properties in care become home to winter visitors. They include bats. The location of their hibernation sites is something of a mystery, but bat roosts have been identified at the castles of Doune near Stirling, Craignethan near Lanark, and Glenbuchat in Aberdeenshire.
All British bats hibernate, singly or in small groups. In preparation, they have to bulk up their body weight by at least one third, so autumn is a time of frenzied feasting.
They usually see out the winter in old trees and caves, but they also use many man-made structures that mimic caves, such as ruined buildings, tunnels, cellars and ice houses. These places are unlikely to vary in temperature during hibernation. The ideal range for a bat is 0–5° Celsius.
As the bat sleeps through the winter, it enters a state of suspended animation. Its body temperature falls to match that of the surrounding air. Its breathing becomes minimal, as does its heart rate. The heart may slow to as few as six beats a minute – compared with up to 1,000 beats a minute during flight.
During mild spells of the winter, bats may wake up and fly to feed or move to a different site. However, staff at our sites are careful not to disturb them. When they wake, they rapidly increase their body temperature, using up a lot of energy. If this happens too often they will not be able to survive until the spring.
As I mentioned above, ice houses are a favoured location for hibernating bats. An ice house is a precursor to the domestic refrigerator: a cellar-like structure that will remain cool regardless of the weather. They were often built next to large houses, mainly during the 1700s. Doune Castle has an ice house dating from a later period of its long history; and there is also one at Mavisbank House, near Loanhead.
During the winter, ice and snow would be taken into the ice house and packed with insulation such as straw or sawdust. It would remain frozen for many months, often until the following winter, and could therefore be used throughout the summer months.
Ice houses are often found next to curling ponds. These may well have been used for curling matches, but their primary function was to produce ice for the ice house.
One of the main uses of this ice was for the storage of perishable foods, but it could also be used simply to cool drinks, or to allow ice-cream and sorbet desserts to be prepared.
The Victorians were very fond of iced puddings. One example is Nesselrode Pudding, made from chestnuts, vanilla, eggs and, of course, ice. According to tradition it was first created for the Russian diplomat Count Karl von Nesselrode in 1814. It became the most popular iced pudding of the 1800s and was particularly appreciated by the upper classes. I imagine a bat would find it rather refreshing too, when roused from a long sleep by its annual spring awakening.