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Myotis nattereri born and reared by their mothers in a flight room had a mean birth body mass of 3.4 g and forearm length of 17.00 mm. Infants opened their eyes at 6 days old, and they were no longer always found roosting attached to their mothers after this age. They were fully furred at 7-8 days and began to flap their wings at days. Growth was initially rapid and linear until 20 days of age and then slowed. At 58-60 days, mean body mass was 8.8 g (89% of adult mass) and mean forearm length was 40.55 mm (98% of adult length). Juveniles began to fly at 20 days, at which age their forearm length was 93.4% of mean adult value. Forearm data were best fitted by the logistic growth model (k = 0.18; asymptotic length = 40.79 mm for males) and body mass data by the von Bertalanffy equation (k = 0.10; asymptotic mass = 8.42 g for males). Pre-flight growth and development rates were similar to those in other British vespertilionid bats, but M. nattereri showed very rapid development of foraging ability after they began to fly. Mothers suckled only their own infants and transported flightless young between roost boxes, on average every 5.3 days.
Many bats are specialized to detect and capture arthropods from vegetation. As echoes from sitting arthropods and vegetation background overlap strongly, it is difficult for those bats to detect prey by echolocation alone. Within the largest genus of bats, Myotis, at least three species from different sub-clades show a characteristic fringe of hairs on the trailing edge of their uropatagium. All three species are capable of gleaning arthropods from vegetation with this tail membrane. Phylogenetic analyses strongly suggest that these specializations evolved convergently. Therefore, one can hypothesize that the hairs at the rim of the tail membrane have an important tactile and/or mechanical function for gleaning prey from substrate. To assess this question, we used light microscopic techniques to investigate the morphology and innervation of the bristle-like hair fringe, and for comparison, the structure of sensory mystacial vibrissae in Myotis nattereri. The results revealed that the fringe possesses two types of hair: larger guard hairs and smaller vellus hairs. Both hair types are well innervated underneath their sebaceous glands. They are encircled by a piloneural complex, which functions as a stretch and tension receptor. Although the bristle-like hairs are clearly not vibrissal follicle-sinus-complexes, their position, morphology and innervation strongly support a sensory function for prey detection and capture. An additional mechanical function, e.g., brushing prey off substrate, is plausible.
I show that a Natterer's bat (Myotis nattereri) was operantly conditioned to echo cues from a large object; in this case a round bowl full of mealworms. In a subsequent choice experiment the bat preferred the empty, round bowl over an unknown, quadratic bowl filled with prey. I suggest that the quick but transient learning of cues indicating prey rich habitat patches might be adaptive for bats hunting in cluttered environments, where they can often not directly detect prey using echolocation. Therefore, it might be an additional foraging strategy of some gleaning bats to search for specific structural cues indicating a high probability of prey being present.
Numbers of wintering Natterer’s bats Myotis nattereri (Kuhl, 1817) and Daubenton’s bats M. daubentonii (Kuhl, 1817) were monitored at seven study sites (three single large hibernacula and four groups of roosts) in central Poland. The longest monitoring period was 1987–2009, the shortest – 1999–2009. The aim of the study was to find out if the numbers of the two species are stable, or if any trends could be detected. For most of the study period, bats were counted twice during each hibernation season: in autumn (November/December) and in winter (January/February). The numbers of Natterer’s bats show a strong increase all over the study area – a trend similar to that reported earlier from other parts of the country. Daubenton’s bats, on the other hand, declined in the hibernacula located in the north-eastern part of the study area, while in those located in the south-western part their numbers were stable or even slightly increased. A decrease in the numbers of Daubenton’s bats is in contrast with reports from other hibernacula in Poland and elsewhere in Europe, where the species increases in numbers. The changes in the numbers of both studied species could be explained by neither changes in the hibernacula nor weather conditions during the study period, so our results probably reflect changes in the numbers of local populations.
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