Variability of foraging and roosting activities in adult females of Daubenton’s bat (Myotis daubentonii) in different seasons

Novel passive detection approach reveals low breeding season survival and apparent lactation cost in a critically endangered cave bat

Capture-mark-recapture/resight (CMR) methods are used for survival-rate studies, yet are often limited by small sample sizes. Advances in passive integrated transponder (PIT) technology have enabled passive detection or ‘resight’ of marked individuals using large antennas with greater read-ranges than previously possible. We used passively-detected resight data and CMR models to study survival rates of the southern bent-winged bat Miniopterus orianae bassanii, a critically endangered, cave-dwelling bat. Over three years, we used PIT-tagging to monitor 2966 individuals at the species’ largest breeding aggregation, using daily detection data (> 1.6 million detections) to estimate seasonal survival probabilities, structured by age, sex and reproductive status, and parameterise population projection matrices. This has hitherto been impossible using traditional CMR methods due to disturbance risk and low recapture rates. Bats exhibited lowest apparent seasonal survival over summer and autumn, particularly for reproductive females in summer (when lactating) and juveniles in autumn (after weaning), and high survival in winter. Lowest survival rates coincided with severe drought in summer–autumn 2016, suggesting that dry conditions affect population viability. Under all likely demographic assumptions, population projection matrices suggested the population is in deterministic decline, requiring urgent action to reduce extinction risk. Passively-collected resight data can now be used in combination with CMR models to provide extensive, robust information for targeted wildlife population management.

The influence of night length: Activity of the northern bat Eptesicus nilssonii under conditions of continuous light in midnight sun compared to a southern population

Background

Nearly all insectivorous bats (Chiroptera) are strictly nocturnal, flying and feeding only between sunset and sunrise despite lower insect availability than by day, most likely to avoid predation by diurnal birds. This may represent a great challenge to bats living north of the Arctic Circle, which are exposed to bright nights in the period of the midnight sun. The northern bat Eptesicus nilssonii was studied at different latitudes in Norway (69, 66 and 58°N) by three techniques; visual counts of exits from and returns to roosts, infrared detection with a datalogger and an ultrasound data recorder, to reveal how their activity varied across latitude, season, and night, as well as across light levels. How does a nocturnal bat adjust to perpetual light and what light levels are tolerated?

Results

In the north the bats’ active season lasted 2.5 months, 1.5 months shorter than in the south. The bats only flew in 3-4 weeks of midnight sun, and hardly ever left the roost until the sun went behind a hill in the evening. In addition, the timing of their nightly hunting was highly influenced by the darkness of the sky, and they very rarely flew in light levels above 200 foot-candles (FC). As the night became darker than twilight from early August, the bats restricted their activity to between sunset and sunrise. This was the normal situation in southern Norway, where the bats tracked sunset and sunrise throughout the entire season. Those bats appeared to prefer light levels below 100-50 FC and hence, also did fly in twilight conditions.

Conclusions

The willingness to fly in twilight by the southern population may be a prerequisite to the northern bat’s survival in the land of the midnight sun. These bats must accept short nights in the first part of their summer season and must be willing to fly in light levels 2-4 times higher than in the south. Most likely, this depends on a reduced predation risk and good abundance of insects at night.

Adult males in maternity colonies of Daubenton’s bat, Myotis daubentonii: what are they?

During summer, females of temperate zone bats form maternity colonies consisting almost exclusively of mothers and their offspring. However, in some species the proportion of males in nurseries is relatively high. We explored the presence of these males in Daubenton’s bat, with respect to their age and relatedness to the local maternity colony. Using automatic PIT-tag readers, we recorded individual swarming activity at roosts used for day roosting and discovered that most of the males were yearlings that returned to their nursery roost after hibernation. The elevated occurrence of yearling males in spring could be explained by late mating attempts or toleration in the territory of adults.

Following the water? Landscape-scale temporal changes in bat spatial distribution in relation to Mediterranean summer drought

Understanding how the spatial distribution of ecological resources shapes species' diversity and abundance in human-modified landscapes is a central theme in conservation biology. However, studies often disregard that such patterns may vary over time, thereby potentially missing critical environmental constraints to species persistence. This may be particularly important in highly mobile species such as bats, which are able to track temporal variations in spatial resource distribution. Here we test the hypothesis that bats in Mediterranean landscapes are strongly affected by the progressive reduction in water availability during the seasonal summer drought. We analyzed the effects of landscape composition and structure on bat diversity and activity, during pregnancy, lactation, and postlactation periods, and identified the most influential variables within and across periods. Water bodies showed the strongest positive effect on bats, followed by riparian habitats and areas with steeper (>30%) slopes. However, while during pregnancy, there were only small landscape effects, these increased during lactation and postlactation, highlighting a progressively stronger association with water habitats during the summer drought. The spatial projection of habitat models showed that the landscape distribution of bat diversity and activity hotspots changed markedly over time. During pregnancy, the spatial pattern of hotspot distribution was weakly defined, while during lactation and particularly postlactation, there was a concentration of hotspots along permanently flowing watercourses. Our study highlights that permanently flowing watercourses are critical for bat conservation in Mediterranean landscapes, calling for measures to counteract their ongoing degradation due in particular to climate change, water abstraction and damming. More generally, our study underlines the importance of considering the temporal dimension in habitat selection studies, without which there is the risk of overlooking the importance of habitats that are key for species persistence only at certain times of the year.

Lyssavirus-reactive antibodies in Swedish bats

INTRODUCTION

To study the presence of European bat lyssavirus (EBLV) infections in bat reservoirs in Sweden, active surveillance was performed during the summers from 2008 to 2013.

MATERIAL AND METHODS

Bat specimens were collected at >20 bat colonies in the central, southeastern, and southern parts of Sweden. In total, blood and saliva of 452 bats were examined by a virus neutralization test and by reverse transcription polymerase chain reactions (RT-PCRs).

RESULTS AND DISCUSSION

EBLV neutralizing antibodies were detected in 14 Daubenton's bats (Myotis daubentonii), all trapped in Skåne or Småland (south and southeast of Sweden). The result was not unexpected since EBLV has been shown to be present in many neighboring countries, for example, Denmark, Finland, Germany, and Norway. However, Sweden has been regarded free of rabies in terrestrial mammals since 1896. Although very rare, spillover of EBLV into other animals and humans have occurred, and the risk of EBLV infection to other species including humans should not be ignored. This is the first report of lyssavirus infection in Swedish bats.

The influence of reproductive condition and concurrent environmental factors on torpor and foraging patterns in female big brown bats (Eptesicus fuscus)

Unlike many other mammals, bats in temperate regions employ short bouts of torpor throughout the reproductive period to maintain a positive energy balance. In addition to decreasing energy expenditure during the day, they typically alter foraging patterns as well. It is well known that various environmental conditions influence both torpor and foraging patterns, but studies of these factors often have focussed on one element in isolation thus it is not known how the two behaviours are collectively influencing temperate bats. The objective of our study was to assess how reproductive condition and environmental factors concurrently affect energy balance in female big brown bats (Eptesicus fuscus). We equipped pregnant and lactating bats in southwest Saskatchewan, Canada with temperature-sensitive radio-transmitters. While transmitters were active, skin temperature data were collected and foraging patterns were determined using triangulation. Of the various environmental and physiological parameters used to model torpor characteristics, roost type was the most important factor. Bats roosting in trees used deeper and longer torpor bouts than those roosting in buildings. Lactating bats had a tendency to forage for longer durations than pregnant bats, and often made more foraging trips. When taken together, we found that foraging duration and torpor duration were not directly related during pregnancy, but exhibited an inverse relationship during lactation. This provides support for the hypothesis that there are physiological trade-offs for reproductive bats and suggests that how bats compensate is not entirely predictable based on current environmental conditions.

Bat rabies surveillance in Finland

Background

In 1985, a bat researcher in Finland died of rabies encephalitis caused by European bat lyssavirus type 2 (EBLV-2), but an epidemiological study in 1986 did not reveal EBLV-infected bats. In 2009, an EBLV-2-positive Daubenton’s bat was detected. The EBLV-2 isolate from the human case in 1985 and the isolate from the bat in 2009 were genetically closely related. In order to assess the prevalence of EBLVs in Finnish bat populations and to gain a better understanding of the public health risk that EBLV-infected bats pose, a targeted active surveillance project was initiated.

Results

Altogether, 1156 bats of seven species were examined for lyssaviruses in Finland during a 28–year period (1985–2012), 898 in active surveillance and 258 in passive surveillance, with only one positive finding of EBLV-2 in a Daubenton’s bat in 2009. In 2010–2011, saliva samples from 774 bats of seven species were analyzed for EBLV viral RNA, and sera from 423 bats were analyzed for the presence of bat lyssavirus antibodies. Antibodies were detected in Daubenton’s bats in samples collected from two locations in 2010 and from one location in 2011. All seropositive locations are in close proximity to the place where the EBLV-2 positive Daubenton’s bat was found in 2009. In active surveillance, no EBLV viral RNA was detected.

Conclusions

These data suggest that EBLV-2 may circulate in Finland, even though the seroprevalence is low. Our results indicate that passive surveillance of dead or sick bats is a relevant means examine the occurrence of lyssavirus infection, but the number of bats submitted for laboratory analysis should be higher in order to obtain reliable information on the lyssavirus situation in the country.