Mammals

Bats (Chiroptera)

With more than 1200 species, bats (order Chiroptera),  make one of the largest groups of mammals (Mammalia). They are unique among mammals because of their ability to fly, for which they developed specific adaptations. Their wing membrane is composed of a double layer of skin with blood vessels, nerves and muscle fibres, and it encloses the fore and hind limbs. Four fingers in bats forearms are greatly elongated, and gave this order its name, which in translation means „hand wing“ (Greek cheir – hand, pteron – wing). The body of a bat is covered in fur, and females give birth to a live young that feeds on milk. In Croatia, 34 bat species have been recorded.

Different bat species use different roosts. In the active period from spring to the middle of autumn, they inhabit warmer shelters: warmer caves, crevices, tree holes, fractured barks, house and church attics, etc. Some species in Croatia have been recorded in caves only, like Longfingered bat (Myotis capaccinii). In winter, they hibernate in underground roosts like caves, pits, tunnels or mines. Caves represent a very important bat roost, and half of all bat species found in Croatia have been recorded in caves, either while forming maternity colonies, in hibernation, migration or swarming. While some species use caves constantly, some use them only in unfavourable conditions. Bats are faithful to their roosts and will use the same roost for many years, and the loss of a roost is not desirable because the alternative roost does not necessarily provide the ideal conditions necessary for their survival.

All temperate-zone bats spend the unfavourable winter period in hibernation. Before winter, they migrate to cooler roosts that are more suitable for hibernation. Hibernation period starts in November or December and lasts until April or May, depending on general climatic conditions. Bats hibernate individually, in smaller groups or in bigger colonies. During hibernation, bats use complex regulatory mechanisms to reduce the number of heart beats, breeding frequency and body temperature, in order to slow down metabolic processes and spend the minimum amounts of energy. Their body temperature reaches values that are only 1 to 2 °C higher than the surrounding environment. In this period, they are particularly sensitive to disturbance. Waking up from hibernation is energetically demanding and causes the to spend energy supplies that are needed for the survival of winter. Harsh winters may cause death of bat individuals with lower fitness and smaller energy reserves.

In the temperate zone, bats mate mainly in autumn and sometimes in winter sites, but in most species the fertilization itself is delayed until spring. Females of one or more species gather into maternity colonies where they raise their offspring and usually give birth to one young in May or June. Maternity roosts are characterized by higher temperatures that are suitable for youngsters. These colonies are especially sensitive to any kind of disturbance, which may cause abortion of pregnant females ormothers that fail torecognize their young due to stress. In just a couple of months, young bats have to learn flight, echolocation and hunting techniques in order to successfully gather reserves of adipose tissue and find a suitable wintering site. That is why bat populations are hard to sustain, and juvenile mortality is high.

Many bat species migrate in spring and autumn in search of suitable maternity, summer or winter roosts. They exhibit high site fidelity, and usually return to the same sites each year. Some species, like Nathusius pipistrelle (Pipistrellus nathusii), can migrate as much as 2000 km, whereas resident species, like Common pipistrelle (Pipistrellus pipistrellus), move to areas that are only 50 km away.

More than 750 bat species use echolocation for orientation and hunting. They produce high frequency signals (between 11 and 212 kHz) that bounce back from objects in space and return to bats` ears, allowing them to recognize obstacles and pray. European bat species feed on insects or spiders within a species specific microhabitat (above water, above canopy level, along the forest edge or around street lamps taking prey from leaves, branches or ground). Since they control populations of night insects, they have a vital role in the conservation of natural ecosystems and are considered to be a natural pesticide. Number of bat species in an area also indicates the state of ecosystem preservation, which is why bats are considered an indicator species.

On the UNEP/Eurobats List of internationally important underground sites for bat species, 55 sites are from Croatia.

BIBLIOGRAPHY:

Some bat species recorded in caves in Croatia

Rhinolophus blasii Blasius` horseshoe bat

Medium-sized horseshoe bat with a horseshoe-shaped flap of skin around the nostrils. As opposed to Greater and Lesser horseshoe bat, they do not wrap themselves in their wing membranes in a cloak-like manner. Inhabits warm caves both in summer and winter.

IUCN category in Croatia: Vulnerable (VU)

Length of head and body: approx. 5 cm

Wing span: approx. 28 cm

Weight: 10 – 14 g

Rhinolophus euryale – Mediterranean Horseshoe Bat

Medium-sized horseshoe bat with a horseshoe-shaped flap of skin around the nostrils. As opposed to Greater and Lesser horseshoe bat, they do not wrap themselves in their wing membranes in a cloak-like manner.

IUCN category in Croatia: Vulnerable (VU)

Length of head and body: 4 – 6 cm

Wing span: approx. 30 cm

Weight: 9 – 14 g

Rhinolophus ferrumequinum Greater Horseshoe Bat

The largest horseshoe bat with a horseshoe-shaped flap of skin around the nostrils. In winter, they wrap themselves in their wing membranes in a cloak-like manner. Young specimens are grey, and older ones more brown in colour.

IUCN category in Croatia: Near Threatened (NT)

Length of head and body: 6 – 7 cm

Wing span: approx. 35 cm

Weight: 18 – 24 g

Rhinolophus hipposideros Lesser Horseshoe Bat

The smallest horseshoe bat and therefore easily identifiable. Has a horseshoe-shaped flap of skin around the nostrils. In winter, they also wrap themselves in wings in a cloak-like manner. Generally they are found individually, usually in winter.

IUCN category in Croatia: Near Threatened (NT)

Length of head and body: approx. 4 cm

Wing span: approx. 20 cm

Weight: 4 – 7 g

Barbastella barbastellus Barbastelle

Medium-sized bat with black ears and muzzle, and fur with yellowish or white on tips, as if frosted. It inhabits crevices in houses and holes in trees (under the bark), and during very cold weather might use caves for hibernation.

IUCN category in Croatia: Data Deficient (DD)

Length of head and body: 4.5 – 6 cm

Wing span: approx. 27 cm

Weight: 7 – 10 g

Eptesicus serotinus Serotine

One of the largest bat species in Europe. Although referred to as a house bat, during the winter it can be found in different roosts: cellars, attics, chimneys and in caves, where it hangs freely on the ceiling or wall, rarely wedged into tight cracks. Not listed in the Red List of Mammals in Croatia.

Length of head and body: 6 – 8 cm

Wing span: approx. 35 cm

Weight: 18 – 25 g

Miniopterus schreibersii Schreiber`s Bat

Relatively easy to identify because its small, triangle shaped ears do not stick out of the fur as in other bat species. Inhabits caves exclusively, both in winter and summer. One of the three most endangered bat species in Croatia.

IUCN category in Croatia: Endangered (EN)

Length of head and body: 5 – 6 cm

Wing span: approx. 35 cm

Weight: 10 – 14 g

Myotis bechsteinii Bechstein’s bat

Bechstein’s bat is a medium-sized bat, specific for its conspicuously long and broad ears. In summer it can be found in forests (tree holes, barks), and in the winter it occasionally comes in caves or cellars where it hangs freely on the ceiling or wall, rarely wedged into tight cracks.

IUCN category in Croatia: Vulnerable (VU)

Length of head and body: 5 – 6 cm

Wing span: approx. 27 cm

Weight: 7 – 10 g

Myotis capaccinii Long-fingered Bat

Medium-sized bat, fur colour is grey to grey-brown. Inhabits caves exclusively, both in winter andsummer, and is generally found further away from the entrance. One of the three most endangered bat species in Croatia.

IUCN category in Croatia: Endangered (EN)

Length of head and body: 5 cm

Wing span: 25 cm

Weight: 7 – 10 g

Myotis daubentonii Daubenton’s bat

Daubenton’s bat is a medium-sized species. Usually it inhabits forests and lives near water surfaces and hibernates in underground sites like caves, mines, wells or basements. Not listed in the Red List of Mammals in Croatia.

Length of head and body: 4 – 6 cm

Wing span: approx. 26 cm

Weight: 6 – 10 g

Myotis emarginatus Geoffroy`s Bat

Medium- sized bat, fur colour is predominantly ginger. Usually it inhabits caves where it hangs individually or in smaller groups, in crevices and holes in walls or ceilings of the cave.

IUCN category in Croatia: Near Threatened (NT)

Length of head and body: approx. 5 cm

Wing span: approx. 23 cm

Weight: 6 – 9 g

Number of bats / m2: approx. 2 000

Myotis myotis & Myotis blythii Greater Mouse-eared Bat & Lesser Mouse-eared Bat

Two largest species of this genus. Very similar and frequently hard to distinguish. Fur colour is gray-brown. Nurseries are generally recorded in entrance areas of the caves. Lesser Mouse-eared Bat is not listed in the Red List of Mammals in Croatia and Greater Mouse-eared Bat is listed as Near Threatened (NT).

Length of head and body: 7 – 8 cm

Wing span: approx. 40 cm

Weight: 20 – 27 g

Myotis nattereri Natterer’s bat

Medium-sized bat that is primarily a forest bat. It hibernates in caves, mines, cellars and abandoned houses. Not listed in the Red List of Mammals in Croatia.

Length of head and body: 4 – 5 cm

Wing span: approx. 26 cm

Weight: 7 – 10 g

Plecotus macrobullaris – Mountain Long-eared Bat

Species with conspicuously long ears (over 38 mm) that are folded back during hibernation and tucked under the wings. Summer roosts are recorded in attics and churches. In winter it occurs in caves where it can be found wedged into tight cracks.

IUCN category in Croatia: Data Deficient (DD)

Length of head and body: 4.6 – 5.5 cm

Wing span: approx. 22 cm

BIBLIOGRAPHY:

  • Antolović, J., Flajšman, E., Frković, A., Grgurev, M., Grubešić, M., Hamidović, D., Holcer, D., Pavlinić, I., Tvrtković N. & Vuković, M. (2006): Crvena knjiga sisavaca Hrvatske. Ministarstvo kulture, Državni zavod za zaštitu prirode, Zagreb. pp. 20-22.
  • Dietz, C & von Helversen, O. (2004): Illustrated identification key to the bats of Europe. Electronic Publication. Version 1.0. Tuebingen & Erlangen. pp 72.
  • Schober, W. & Grimmberger, E. (1987): Die Fledermäuse Europas: kennen-bestimmen-schűtzen. Frank’sche Verlagshandlung, W. Keller&Co., Stuttgart, kosmos Nathurfǘhrer. pp 222.