Energy Conservation

Flying uses a huge amount of energy, far more than any physical work we do. This means that not only do bats need lots of food as fuel, for their size, but they must also do all they can to conserve energy.

Whereas our temperature is constant, changing only a degree or two unless we are unwell, a bat will deliberately change its temperature to save energy when food is not easily available. Dropping their temperature to a low level is known as becoming torpid, and at these times everything in their body works very slowly. This may happen even in the middle of summer if there are few insects about because of bad weather.

When flying a bat’s body temperature may reach 42° C. At the other extreme when hibernating in winter it can drop down to 2° C. Most of the time it’s somewhere in between. By doing this the bat saves energy, rather like our turning down the heating when we want to keep the fuel bills low.

Maternity roost of Natterer's bats

The most energy-expensive time of all is for the mother bats when they are lactating, that is, producing milk in order to suckle their young baby. At this time bats use an extra way of conserving energy. Before the babies are due to be born, the pregnant females gather in what is known as a maternity roost. This means they save on the heating ‘bills’ by keeping close together. and also helps keep the babies warm from the time of birth.