Natterer's bat

GB: Least concern

England: Least concern

Scotland: Least concern

Wales: Least concern

Global: Least concern

Head & body length: 40mm - 50mm

Forearm length: 36mm - 43mm

Wingspan: 245mm - 300mm

Weight: 7g - 12g

Colour: Fur light buff brown on black, white underneath. Bare pink face.

Natterer’s bats have a slow to medium flight, sometimes over water, but more often amongst trees, where their broad wings and tail membrane give them great manoeuvrability at slow speed.

They normally fly at heights of less than 5m, but occasionally may reach 15m in the tree canopy. Much of the prey is taken from foliage and includes many flightless or day-flying insects. Sometimes larger prey is taken to a feeding perch.

Relatively few summer roost sites of Natterer's bat are known. However, most known summer colonies are in old stone buildings with large timber beams, such as castles, manor houses and churches, or large old timbered barns. Crevices in beams or gaps in beam joints are common roost sites. They also roost under bridges.

Although it's rare for Natterer's bat to roost in houses, they can occasionally roost in the roof space or directly under ridge tiles, where they are often hidden amongst timber or tiles. Access to roost sites is often by direct uninterrupted flight through a permanently open aperture, or at the eaves but is sometimes via tortuous routes through hollow walls or behind tiles. There are usually a few droppings below the access point.

The emergence of Natterer’s bats from their roost reaches a peak about one hour after sunset. There is then a lull in activity before the bats begin to return. They have been observed returning an hour or two before sunrise, but when young are present they may do so soon after emergence.

Natterer’s bats start to arrive at their hibernation sites in December with peak numbers in January or early February. Most leave by early March. They show a preference for the cool entrance areas of caves and mines but will hibernate in any underground shelter. Natterer’s bats are one of the species most frequently found in any small cave-like site or even exposed rock crevices. They are usually solitary, but small groups are not uncommon and may include other species. An exceptional cluster of about 150 bats is regularly found at one site.

In their efforts to lodge in small crevices, Natterer's bats can be found in almost any position, including lying on their back or sides, or even resting on their heads. Individual Natterer’s bats are occasionally found hibernating in churches, in crevices between beams.

Natterer's bats eat flies (mainly midges), small moths, caddis flies, lacewings, beetles, small wasps, spiders.

Natterer's bat mate in the autumn, but has been observed in all winter months.

Maternity colonies of adult females are formed from May-June through to July and sometimes until September-October. They may change roost sites frequently. The female gives birth to a single young at the end of June or in early July. For the first 3 weeks the young bat feeds only on its mother’s milk and is left in a crèche inside the roost when its mother goes out at night to feed. During this time the juvenile may make its first flight inside the roost, and within 6 weeks it is fully weaned and able to forage for itself.

The echolocation calls of the Natterer’s bat are very quiet. Their frequency range is 35 to 80kHz with a peak at about 50kHz. On a bat detector the calls are heard as irregular rapid clicks, with a sound similar to cellophane being crumpled.

Natterer’s bats are found throughout most of the British Isles. Records have extended its range in Scotland, north to the Great Glen fault. Generally it is a scarce and poorly known species.

The UK population of Natterer’s bats is of international importance. To conserve its summer roosts, the conversion of barns should be discouraged and the maintenance and remedial timber treatment of other older buildings need to be carefully monitored. Important wintering sites should be protected. Feeding habitat requirements are poorly known.