Brown Long-eared Bat Plecotus Auritus Research Articles

Social and population structure of a gleaning bat, Plecotus auritus

Brown long-eared bats Plecotus auritus occupying 30 summer roosts in north-east Scotland were studied over 15 years. During this time 1365 bats were ringed, and a further 720 recaptures were made. Individual bats showed a high degree of roost fidelity, returning to one main roost site; < 1% of recaptured bats had moved among roost sites, and all recorded movements (n= 5) were < 300 m. Adults of both sexes were loyal to the roost sites at which they were first captured, indicating long-term use of roosts. At least some juveniles (n= 32) of both sexes returned to the natal roost. Mark–recapture estimates indicated that colonies of this species were substantially larger (c. 30–50 individuals) than assumed in previous studies. Plecotus auritus differs from most other temperate zone, vespertilionid species in that there was no evidence of sexual segregation during summer, with males present in all colonies throughout the period of occupancy. Population structure in summer seems to be consistent with a metapopulation model, with discrete sub-populations showing minimal interchange. The group size, colony composition and population structure described in this species may be associated with the wing shape (particularly aspect ratio) and foraging behaviour of P. auritus. It is postulated that relative motility, linked to wing structure, may affect the distribution of individuals, and may have implications for the genetic structure of this species. Correlations between aspect ratio and both colony size and migratory behaviour, across British bat species, indicate that wing shape could be an important factor contributing to patterns of social behaviour and genetic structuring in bats.

Morphological changes during postnatal growth and reproduction in the brown long-eared bat Plecotus auritus: implications for wing loading and predicted flight performance

Patterns of postnatal growth, and changes in mass and wing loading during reproduction were studied in captive free-flying brown long-eared bats (Plecotus auritus, Linnaeus, 1758). The bats were fed on noctuid moths occasionally supplemented with mealworms. Growth in body mass was best described by the von Bertalanffy model (n = 5 individuals), while growth in forearm length, wingspan and wing area, were best described by the logistic equation (n = 5 individuals). Because the wings developed more rapidly than body mass, wing loading decreased from high levels following birth to a minimum at around 30 days of age. Predicted mechanical power requirements for flight (minimum power Pmp and maximum range power Pmr) and the corresponding flight speeds (Vmp and Vmr) as well as the minimum theoretical radius of a banked turn (rmin) also reached minima at this time. At 30 days of age juveniles could fly with lower predicted power requirements and were more manoeuvrable (could fly more slowly at minimum power and make tighter turns) than adults. These minima corresponded to the time when juveniles first left the roost box to fly. Reproductive females (n = 6) displayed a near two-fold increase in body mass and wing loading over 50 days prior to birth. This resulted in a three-fold increase in the predicted mechanical power requirements for flight (Pmp and Pmr), and a decrease in predicted flight manoeuvrability. Non-reproductive individuals (n = 22) had a similar pattern but increased in body mass and wing loading to a lesser extent. Over days 1 to 40 postpartum, both mass and wing loading declined in lactating females, but continued to increase in the non-reproductive bats.

Population genetic structure and gene flow in a gleaning bat, Plecotus auritus

During summer the brown long-eared bat Plecotus auritus (Vespertilionidae) forms stable colonies, comprised of both adult females and males and young of the year. A long-term ringing study conducted in north-east Scotland has established that little movement occurs among colonies and that both sexes are recruited into their natal colony. The aim of the present study was to investigate, using microsatellite DNA markers, if genetic structure within the population reflects the spatial structure indicated by ringing. Inter-colony FST estimates obtained for all colony members, and for females and males separately, were low (0.019, 0.026 and 0.011, respectively), but all values differed significantly from zero. These data indicate high gene flow between colonies, although some coancestry among colony members is evident in both sexes. On combining the ringing and genetic data, it is concluded that gene flow occurs via extra-colony copulation, rather than natal dispersal, and that each colony behaves as a distinct subpopulation. Microgeographical genetic isolation by distance was demonstrated for, to our knowledge, the first time in a bat species, and found to be apparent both across the entire study area and along one river valley. The results suggest that extensive macrogeographical population genetic structure may be evident across the species' range.

Roost Selection by the Brown Long-Eared Bat Plecotus auritus

1. One of the key threats to bats in Britain is loss of suitable roost sites, but little is known about roost requirements for most species. 2. Roost selection in the brown long-eared bat Plecotus auritus was demonstrated by comparison of buildings used as summer roosts in north-east Scotland with (i) random buildings in the same area, and (ii) a set of adjacent houses located in the same habitat. 3. Buildings containing roosts were situated closer to woodland and water relative to the random houses, and also had a greater area of woodland within a radius of 0.5 km, but not at distances beyond this. This suggests that feeding habitat in the vicinity of the roost is important for roost selection. 4. When compared with adjacent houses, roosts were older, and had roof spaces divided into more compartments, which were more likely to be fully lined with rough wooden planking. 5. The temperatures inside summer roosts (mean 17.9°C) were significantly warmer than those from random and adjacent houses (mean 16.7°C). 6. These results suggest that P. auritus is selective of its roosts, relative to the houses available. 7. The selection of specific types of roosts by P. auritus has implications for the management advice provided when roosts are threatened, and conservation actions should focus on efforts to avert significant change to, or destruction of, roost sites or the woodland in their vicinity.

Addition of Artificial Loads to Long-Eared Bats Plecotus Auritus: Handicapping Flight Performance

ABSTRACT A series of experiments is described in which two brown long-eared bats Plecotus auritus Linnaeus (Chiroptera: Vespertilionidae) were flown in a 1 m ×1 m×4.5 m flight enclosure at a range of body masses (n=9 experiments for a female bat, and n=11 for a male bat). The highest three of these masses incorporated artificial loads. Stroboscopic stereophotogrammetry was used to make three-dimensional reconstructions (n=124) of the bats’ flight paths. Over the entire range of experiments, wing loading was increased by 44% for the female and 46% for the male bat. Effects arising from captivity were controlled for: experiments at certain wing loadings were repeated after a period in captivity and the response to load was found to be unaltered. Flight speed fell with total mass M or with wing loading, varying as M−0.49 in the female and M−0.42 in the male bat. Wingbeat frequency increased with total mass or wing loading, varying as M0.61 in the female and M0.44 in the male bat. Hence frequency, but not speed, changed with mass in the direction predicted by aerodynamic theory. These results were used in a mathematical model to predict wingbeat amplitude, flight power and cost of transport. The model was also used to estimate the optimal flight speeds Vmr and Vmp. The model predicted that amplitude increases with load. Measurements of wingbeat amplitude did not differ significantly from the predicted values. The observed flight speed was below the predicted minimum power speed Vmp (which increases with load), and diverged further from this with progressive loading. The increase in cost of flight calculated by the model over the range of wing loadings was approximately double that which it would have been had the bats adopted the optimal approach predicted by the model. The limitations inherent in the theoretical model, and the possible constraints acting on the animals, are discussed.