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Like other small terrestrial mammals, bats have a high mass-specific energetic demand because of the fact that they have an unfavorable surface area to volume ratio. Furthermore, bats have a very energy-expensive mode of locomotion: flight. This high energetic demand has to be covered by food intake. The retention time of the digestive tract is one factor affecting the energy intake of bat species. Factors like energy demand, gut volume and dietary specialization influence retention time in mammals. However, maximum retention time for only Myotis myotis and transit time only for M. lucifugus, Nyctophilius gloudi and Nyctalus noctula is known. This study investigated the maximum retention times and transit times of 10 Central European bat species. It was hypothesized that the level of specialization of the digestive tract, energy-demanding processes and intestine length would affect the retention time of bats. Fluorescence-marked mealworms Tenebrio molitor were used to measure the time between the first ingested mealworm and the first appearance of the marker or the last fluorescing feces, respectively. For the first time, the retention time of 10 insectivorous bat species was measured to determine interspecific differences. Additionally, we measured the retention time of post-lactating female and spermatogenically active male Pipistrellus pipistrellus to determine intraspecific differences. The retention time of bats differed significantly between species and is probably influenced by the level of specialization of the digestive tract. High-level specialization of the digestive tract resulted in short retention times. Furthermore, significant intraspecific differences between postlactating and spermatogenically active individuals of P. pipistrellus showed that the retention time within a single species might be influenced by energy-demanding processes (e.g. reproduction).

The parasite load of seven European bat species (Myotis daubentonii, Myotis emarginatus, Myotis myotis, Myotis mystacinus, Myotis nattereri, Nyctalus noctula, Pipistrellus pipistrellus) was compared and tested to see if there was a relationship between high parasite load and poor body condition in bats. Considerable variations of the parasite load between host species, ages and sexes were found, which can be attributed to roosting conditions and behavioural differences of the bats. Overall, male bats had the fewest parasites. Very different parasite population densities were found in different years, and also at the same time at different sites. A generally high parasite load during the nursing season was not observed. There was no strong trend of increasing parasite load in bats with decreasing condition. If weak bats had more parasites than other individuals, the high number of parasites seemed to be a symptom and not the direct cause of the bad condition.

Roost selection by tree roosting noctules Nyctalus noctula and Daubenton's bats Myotis daubentonii was determined by comparing roost characteristics with the characteristics of randomly chosen tree cavities in the area. The following parameters were determined for 81 noctule roosts and 27 Daubenton's bat roosts: tree species, type of cavity (woodpecker or natural), entrance height, compass direction of entrance and distance to the edge of the wood. Roost choice of both bat species was similar except that Daubenton's bats used woodpecker cavities less than noctules. Both bat species were selective in their roost choice. Daubenton's bats preferred oaks over beeches, and noctules preferred woodpecker cavities over natural cavities, indicating dependence on woodpeckers. Both bat species preferred to roost close to the edge of the wood. Roosting close to the edge of the wood may reduce commuting flight costs for both species or may be preferable for thermoregulatory reasons.

Pipistrellus pipistrellus, Eptesicus serotinus, Nyctalus noctula, N. leisleri, Myotis daubentonii, M. myotis, unidentified small Myotis spp. and Plecotus spp. were recorded during bat detector transects within a central European city of 350,000 inhabitants. Bats were recorded in all seven habitat types under study, the levels of activity for each species and habitat type were significantly different. The relative activity of the whole bat community was highest in old outskirts (low density housing) and at the river, and lowest in the city centre and new housing estates (high density housing). Significant differences were found in the timing of bat activity during the night and the season. Within the first two hours after sunset, relative activity of P. pipistrellus and E. serotinus was highest in the first 0.5 h and decreased thereafter. In N. noctula, it was highest during the second and third 0.5 h and in Myotis spp. it was low in the first 0.5 h and increased till the end of monitoring. Flying bats were recorded from March till October; the lunar cycle had no significant effect on the amount of flight activity. The relative activity of E. serotinus was positively correlated with temperature. No significant correlation was found between the activity of bats and the number of trees and streetlamps per transect. Comparison with the results of an earlier visual census showed that more bats were recorded acoustically than visually except in the city centre. This is attributed to the effect of white streetlamps during the visual census. During the acoustic census, most white lamps were replaced by yellow lamps which biased the impact of lamps on bat traffic. Nevertheless, bat species known to benefit from white streetlamps remained the most common foragers within the city.

Distribution and minimum population densities for seven UK bat species known to be resident in northern England were calculated in an area covering 2500 km2. The species present were pipistrelle (Pipistrellus pipistrellus), brown long-eared (Plecotus auritus), Daubenton's (Myotis daubentonii), whiskered (Myotis mystacinus), Natterer's (Myotis nattereri), noctule (Nyctalus noctula) and Brandt's (Myotis brandtii). Data were collected primarily from counts at summer roosts over the period 1983 to 1990. A total of 310 bat roosts were discovered within the study area. Of the 256 roosts at which the species present was identified, the majority, 127 (49.6%) were P. pipistrellus, with a mean maternity roost size of 69.6 bats. A minimum population density of 12.6 batskm−2 was estimated for P. pipistrellus, based on summer (maternity) roosts. The minimum population density estimate was higher than previous studies in northern England but substantially lower than those reported in Scotland (18.2 bats km-−2). The combined density of M. mystacinus, M. brandtii, and P. pipistrellus, which have similar foraging styles (15.8 bats km−2), is comparable to Scottish P. pipistrellus densities. The density of M. duubentonii was also lower than in Scotland, although the density of P. auritus was comparable. The majority of summer roosts for all species were found in buildings, except N. noctula and M. duubentonii which used bridges/tunnels or trees.

The noctule Nyctulus noctula (Schreber, 1774) is a relatively large (c. 25 g) insectivorous bat which catches insects on the wing (by aerial hawking). Emergence at a maternity roost was earliest relative to sunset when females were lactating, and bats may then have risked predation by flying at higher light levels during a period of high energy demand. Flight performance was quantified by using stereophotogrammetry. At feeding sites bats flew at 6.0 ± 2.1 m/s. This was faster than predicted minimum power speed (V mp), and either between V mp and maximum range speed (V mr), or close to their predicted V mr, depending on which aerodynamic model of flight power requirements was used. The echolocation behaviour of noctules is flexible. Long duration, low frequency calls (c. 20 kHz) with little frequency modulation were emitted while cruising, but at foraging sites the calls became more frequency-modulated. As the noctule is traditionally thought of as using low frequency echolocation, it was expected to receive weak echoes from small targets and therefore to specialize in eating large insect prey. Although the bats ate mainly beetles, large numbers of small dipterans were also eaten. The noctule is probably able to detect such small items because, when foraging, its calls become broadband and sweep from high frequencies. Higher harmonics are also present, and these may assist in the detection of small prey. In noctules, as in many bats, there appears to be a 1:1 link between wingbeat and call production during the search phase of foraging.

Insectivorous bats have rarely been considered suitable as breeding laboratory animals despite their unique reproductive physiology. The purpose of this study was to compare maternal care and growth of young in several species of British vespertilionids in order to find one or more species that would adapt well to conditions of captivity. During the spring of 1966 and of 1967, 17 noctule (Nyctalus noctula Schreber), eight serotine (Eptesicus serotinus, Schreber), 33 pipistrelle (Pipistrellus pipistrellus, Schreber), and four long-eared (Plecotus auritus, Linnaeus) bats were brought into the laboratory after insemination or when pregnant, and most gave birth. One noctule mated in the laboratory in the autumn of 1966 and gave birth to twins in June 1967, thus providing the first known breeding record of any British vespertilionid in captivity. Noctules (13) housed in near natural conditions with limited food gave birth four weeks after others (four) fed ad lib. and housed in a room which buffered the changes in external temperature, and two long-eared bats gave birth in late May (the normal birth season is June to July). These early births may have resulted from premature ovulations and/or a shortened gestation. Fourteen of 17 live-born noctules, all live-bom serotines (four), 12 of 14 live-born pipistrelles, and none of the long-eared bats were reared to weaning age. As part of maternal care all females allogroomed and retrieved their young until the second week post-partum, and recognition of offspring seemed to be effected primarily by sound and individual odour. Neonates of three species were about 20% of the mother's weight at birth and doubled their weight by the end of the second week. Forearm growth ceased at approximately five weeks of age. Weaning, which was assisted, was completed by the end of the second month and adult weight was reached soon thereafter. The development of the three species, i.e. the opening of the eyes, hair growth, and the replacement of the deciduous teeth, differed, and the pipistrelles and serotines developed more rapidly than the noctules.