Bats are the world's only flying mammal and they comprise about one quarter of all the worlds mammal species.
All British bats are insectivorous, and in a group called ‘microchiroptera’; in contrast to the ‘megachiroptera’ group which are also called the fruit bats There are no native fruitbats in Britain, and also no vampire bats. British bats consume many billions of insects such as midges, gnats and flies each summer, some specialise in moths. In general they are a good indicator of the condition of our countryside: lots of bats show healthy ecosystems and that the plants and other animals are doing well. Sadly there are not so many bats as one would expect in this country….which is one of the reasons bats are so heavily protected by international laws. Bats are very long-lived mammals, with even the small pipistrelle species potentially living 15 years in the wild. Brant’s bats have been found at over 41 years old.
Although they have quite good eyesight, they hunt in the dark so emit their own sonar called echolocation which they use to find their prey and navigate with incredible accuracy. For this reason they are unlikely to crash into you so the myth about bats becoming tangled in hair is just that! These echolocation calls are at a very high frequency (usually between 20 - 110 kHz) so humans cannot hear them very well, which is why we use bat detectors.
A year in the life of a bat
In the summer, females gather together to form maternity roosts where they give birth and raise their young. Females usually only have one baby a year; twins are rare and often they take a year out from breeding. Maternity roosts are often in trees, buildings or barns. Babies are usually born in June or July. After about four weeks the young are almost full size and can fly around with their mother. Males do not take part in the rearing of young, and in many species the males have their own small roosts away from the maternity roosts.
Bats usually mate in the autumn, in some species they fly about cave or building entrances to meet each other, in others the males call to females from a perch. Occasionally mating also occurs in the winter. The females store the sperm throughout the entire winter, and wait until the spring to ovulate and fertilize the egg. This enables the females to wait until they perceive the conditions to be right to become pregnant. They can also slow pregnancy if conditions get worse and food is scarce or the weather very cold. This reproductive strategy is unique to bats.
In winter, when insects are scarce, bats hibernate. They choose places that heat and cool slowly, usually in caves, cold parts of buildings or hollow trees. Warm weather or disturbance can cause them to wake, using precious reserves of stored energy, which may cause them to run out before spring and die. Studies indicate nearly half of young bats do not survive their first hibernation. We still only know where a very small proportion of the bat population in Britain go to roost and hibernate, unfortunately some of the ones we know about are because people have accidentally discovered the bats during hibernation and the roost has run into problems.
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