Series: Schriftenreihe für Landschaftspflege und Naturschutz Volume: 66
374 pages, plates with 41 colour photos; b/w illustrations, colour maps, tables
Language: German, with trilingual summary in English, German, and French (2 pp.)
This report on "Bats in Forests" encompasses the results of a three-year research and development project, involving more than 100 experts and bat workers.
Besides a thorough search of the relevant literature, we also studied the occurrence and ecology of several bat species in forests. The focus was on radiotracking species for which very little ecological data had been available: barbastelle, Brandt's bat, Leisler's bat, Natterer's bat, Bechstein's bat, Nathusius' pipistrelle. Using a variety of approaches (netting, bat detectors, checking of roost sites including nest boxes and tree holes), the bat faunas of a set of different forests were determined. One subproject dealt with riverine forests and their relevance for the migrating species noctule bat and Nathusius' pipistrelle. Additional information an the use of riverine forests during migration was gathered through direct observation of migrating bats, and by banding and recapture of bats. In several investigated areas stands were mapped according to a specially developed key. The resulting forest type distibutions were overlaid with the radiotracking data of the respective bats.
All 20 bat species which regularly occur in Germany make use of the habitat "forest" in some way. The following species regularly rear young in forests: Bechstein's bat, Natterer's bat, brown long-eared bat, noctule, Leisler's bat, Brandt's bat, Dauberton's bat, barbastelle, Nathusius' pipistrelle. whiskered bat, Geoffroy's bat, greater mouse-eared bat and the common pipistrelle (incl. "55 kHz-type") only occasionally stay in natural tree holess or nest boxes. In most of these cases single males were found. Nursery colonies of these species have only very rarely been observed in forests. In almost all species, however, forests, forest edges, and canopy gaps are parts of their hunting grounds regularly. In decreasing order of the intensity of usage, we find Bechstein's bat (almost nowhere else), greater mouse-eared bat, barbastelle. brown long-eared bat, Nathusius' pipistrelle, Natterer's bat, Brandt's bat, lesser horseshoe bat, greater horseshoe bat, whiskered bat, Leisler's bat, Geoffroy's bat, serotine, Daubenton's bat, grey long-eared bat, northern bat, common pipistrelle, noctule, pond bat, and particoloured bat.
Holes in trees and cracks behind bark represent the most important roost sites for bats in forests. Holes may be caused by rotting and/or through the work of woodpeckers. The single species prefer certain roost sites. A new and very significant finding for forest management is that barbastelles almost exclusively use cracks behind bark as a roost site. Bats very often, sometimes daily, move from one roost site to the next indicafing a for a high density of potential roost sites. A minimum required number of available roost sites of 50 was estimated for a nursery colony of Bechstein's bat. For other species a similarly high number of required roost sites has been documented.
Depending on their flight behaviour and hunting strategy, bats use all strata of the forest from the free air space above the canopy down to the forest floor (e.g. Leisler's bats hunt in the free air space, Bechstein's bats close to the vegetation, greater mouse-eared bats over and on open floor). Moreover, different bat species may be attributed to different developmental stages of forest stand. Some species target high insect densities, for example in canopy gaps and small clearings.
Depending on the bat species, the size of hunting grounds and the area used by an individual bat range from a few hectares to more than one hundred. Individual Bechstein's bats very faithfully returned to the same hunting grounds, even over several years. Therefore, the long-term availability of a forest habitat is an important conservation issue. The minimum area and the optimal habitat for a breeding colony of 20 Bechstein's bats was calculated to be 250-300 ha of deciduous forest rich in structure and with little undergrowth (ca. 20-30%).
Most likely, a colony hunting in a less stuctured forest, e,g, a coniferous forest, has to disperse over a larger area. The minium area for a breeding colony of 270 greater mouse-eared bats was estimated at 80-90 km2. The most important type of stands for this species offers open forest floor used for hunting ground beetles (carabids).
From the project results we derived recommendations for forest management which are intended to serve bat conservation.
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