Schreiber's long-fingered bat - MINIOPTERUS SCHREIBERSII

Schreiber's long-fingered bats congregate in caves in densely packed colonies of up to 300 000 during the day. The interfemoral membrane is skilfully employed as a scoop to catch insects in flight. The most outstanding biological characteristic of this species is its occurrence in immense colonies in the deep, dark interiors of caves (colonies of up to 300 000 individuals have been recorded) and it is therefore restricted to areas that offer suitable roosting sites. The heat generated by such a mass of bats can alter the temperature of a cave, and this is often employed to manipulate optimum temperatures for nursing colonies during summer. These nursing colonies are typically found in domes, where the warmer air is trapped.Research on a colony of 300 000 Schreiber’s long-fingered bats residing in the guano caves at the De Hoop Nature Reserve near Bredasdorp in the Western Cape, vividly illustrates the important role of bats in an ecosystem. It was estimated that during the eight months that this colony uses the caves as its summer residence, at least 100 metric tons of insects are consumed. This prey is apparently hunted within a radius of 15 kilometres. Guano was mined from the caves in earlier years, but since then tons of the material have again accumulated and will in time fill the cave and deprive the colony of its roost. While disturbance of roosting colonies is strongly to be discouraged, controlled guano mining is clearly in the long-term interest of this and similar colonies.The long and narrow wing morphology of the bat enables it to fly very fast but, by the same token, prevents it from being very acrobatic, and it prefers uncluttered air space in which to forage.Banding experiments in the Pretoria environment showed that the species, like other insectivorous bats, may live for 20 years or more. Other small mammals of similar size have a life expectancy of two year at most. The reason for bats attaining such disproportionate longevity remains a mystery, but may be related to their ability to enter torpor to conserve energy. Distribution and Status Of all bats, probably once of the most widely distributed – found in Europe, India, Australia, and the Far East. In Africa it is known from the extreme north and most of sub-Saharan Africa excluding the arid regions and the tropical areas of central West Africa. A common species, but sensitive to disturbances, especially during winter. Habitat Deep, dark, moist interiors of caves, where they congregate by day in densely packed colonies. An abundant food supply in summer is crucial. Particulars of the habitat over which the species preys seem to be less significant as it survives in various plant and physiographical associations. Field Characteristics Average body length of 110 millimetres and mean weight of 10 grams. The fur on the back is very dark brown or charcoal, and on the abdomen is slightly lighter. The wings are long and pointed; wing and interfemoral membranes are dark. The snout is shortened and the skull highly domed, although the latter is obscured by dense fur. The 3 different species of long-fingered bat occurring in the region are not easily distinguished from one another. Breeding Biology Copulation and fertilization occur in autumn. Females are pregnant when they enter hibernation; foetal development is delayed to facilitate birth 8 month later, after the first rains in early summer. A single pup is born. Pups are tended by their mothers in separate nursery colonies until they are old enough to fend for themselves. Sounds Echolocation calls are at a high frequency, inaudible to the human ear. When disturbed during the day may utter high-pitched alarm calls. Food and Feeding Methods Subsists on a variety of small, soft bodied insects, which are hunted on the wing at night. Insect concentrations over water are a rewarding source of prey. Social System Highly gregarious; colonies numbering hundreds of thousands are know. Individuals form closely packed clusters, sometimes even piled on top of each other. Migrates seasonally over distance of about 250 kilometres. During winter prefers cool, damp caves in which to hibernate, and at the end of summer migrates to caves in warmer areas, where there is a abundance of insects to sustain the immense numbers that constitute a colony. (Dr Naas Rautenbach)