135,100 research outputs found
Size constancy in bat biosonar?
No full textPerception and encoding of object size is an important feature of sensory systems. In the visual system object size is encoded by the visual angle (visual aperture) on the retina, but the aperture depends on the distance of the object. As object distance is not unambiguously encoded in the visual system, higher computational mechanisms are needed. This phenomenon is termed "size constancy". It is assumed to reflect an automatic re-scaling of visual aperture with perceived object distance. Recently, it was found that in echolocating bats, the 'sonar aperture', i.e., the range of angles from which sound is reflected from an object back to the bat, is unambiguously perceived and neurally encoded. Moreover, it is well known that object distance is accurately perceived and explicitly encoded in bat sonar. Here, we addressed size constancy in bat biosonar, recruiting virtual-object techniques. Bats of the species Phyllostomus discolor learned to discriminate two simple virtual objects that only differed in sonar aperture. Upon successful discrimination, test trials were randomly interspersed using virtual objects that differed in both aperture and distance. It was tested whether the bats spontaneously assigned absolute width information to these objects by combining distance and aperture. The results showed that while the isolated perceptual cues encoding object width, aperture, and distance were all perceptually well resolved by the bats, the animals did not assign absolute width information to the test objects. This lack of sonar size constancy may result from the bats relying on different modalities to extract size information at different distances. Alternatively, it is conceivable that familiarity with a behaviorally relevant, conspicuous object is required for sonar size constancy, as it has been argued for visual size constancy. Based on the current data, it appears that size constancy is not necessarily an essential feature of sonar perception in bats
Vertical variation in flight activity of the lesser short-tailed bat in podocarp and beech forests, Central North Island, New Zealand
No full textDesigning robust monitoring programmes for cryptic species is particularly difficult. Not detecting a species does not necessarily mean that it is absent from the sampling area. A conclusion of absence made in error can lead to misguided inferences about distribution, colonisation and local extinction estimates, which in turn affects where and how conservation actions are undertaken. It is therefore important to investigate monitoring techniques that reduce the non-detection rate of cryptic species. As habitat complexity plays an important role in the activity of bats within a forest, it was hypothesised that the amount of vegetative ‘clutter’ present at different heights within two different forest types affected the flight activity of lesser short-tailed bats (Mystacina tuberculata). This could affect detection of the species within different forest structures. To compare bat activity at three heights – top (22.0–25.0 m), middle (10.0–12.0 m) and bottom (1.5–2.0 m) – within a podocarp and a beech forest we used automatic bat monitors during January to March 2005. The number of bat passes was recorded at each height at two study areas within each forest and compared between forest types. The forest structure was described using the Recce method and vegetative cover estimated within the three height tiers sampled for bat activity. Within both forest types, the middle-level bat detectors logged the greatest amount of activity. However, differences between the forest types were most pronounced closer to the ground, where a high amount of activity was detected within the beech forest, and very little within the podocarp forest. This suggests that flight activity of lesser short-tailed bats may be affected by the level of vegetative clutter found at different heights within a forest. When designing monitoring programmes for lesser short-tailed bats, it is recommended that consideration be given to the forest structure and how this may affect detection of bat activity
Experimental Evidence for the Effect of Small Wind Turbine Proximity and Operation on Bird and Bat Activity
No full textThe development of renewable energy technologies such as wind turbines forms a vital part of strategies to reduce greenhouse gas emissions worldwide. Although large wind farms generate the majority of wind energy, the small wind turbine (SWT, units generating <50 kW) sector is growing rapidly. In spite of evidence of effects of large wind farms on birds and bats, effects of SWTs on wildlife have not been studied and are likely to be different due to their potential siting in a wider range of habitats. We present the first study to quantify the effects of SWTs on birds and bats. Using a field experiment, we show that bird activity is similar in two distance bands surrounding a sample of SWTs (between 6-18 m hub height) and is not affected by SWT operation at the fine scale studied. At shorter distances from operating turbines (0-5 m), bat activity (measured as the probability of a bat "pass" per hour) decreases from 84% (71-91%) to 28% (11-54%) as wind speed increases from 0 to 14 m/s. This effect is weaker at greater distances (20-25 m) from operating turbines (activity decreases from 80% (65-89%) to 59% (32-81%)), and absent when they are braked. We conclude that bats avoid operating SWTs but that this effect diminishes within 20 m. Such displacement effects may have important consequences especially in landscapes where suitable habitat is limiting. Planning guidance for SWTs is currently lacking. Based on our results we recommend that they are sited at least 20 m away from potentially valuable bat habitat
Bat community structure and habitat use across logging regimes in jarrah eucalypt forests of south-western Australia
No full textIn many parts of the world, the increasing demand for timber and other forest products has led to loss, fragmentation, degradation or modification of natural forest habitats. The consequences of such habitat changes have been well studied for some animal groups, however not much is known of their effects on bats. In Australia, logging of native forests is a major threat to the continent‘s biodiversity and while logging practices have undergone great changes in the past three decades to selective logging (including ecologically sustainable forest management), which is more sympathetic to wildlife, there is still concern about the effects of logging on the habitat of many forest-dwelling animals. The goal of this thesis was to investigate the effects of logging on the bat species assemblages at both community and individual species levels in terms of their foraging and roosting ecology in jarrah forests of south-western Australia. This information is necessary to strengthen the scientific basis for ecologically sustainable forest management in production forests. The outcome of this research may help in the formulation of policy and management decisions to ensure the long-term maintenance and survival of viable populations of forest-dwelling bats in these altered environments. Bats were selected because they comprise more than 25% of Australia‘s mammal species and constitute a major component of Australia‘s biodiversity. In addition, bats play key roles in forest dynamics and may act as indicators of disturbance. In the jarrah forests, bats are a significant proportion of the mammal fauna (9 of around 30 native extant species).
As a basis of understanding how bats use modified habitats, nine species of bats were investigated by assessing their foraging and commuting habits (measured as bat activity) in different forest types (logged, young regrowth and old regrowth forest). To assess patterns of habitat use across a gradient of managed forest conditions, and to help predict impacts of logging on bats, four replicates were selected from each of three distinct post-harvest management treatments, recently logged forest or gaps ( 30 years old). Sites were monitored for bat activity on two nights, with Anabat detectors placed on track and off-track positions. The relationships between bat species assemblages in terms of their relative use and foraging activity and various forest structural variables, and the relationship between bats and the insect biomass were examined in order to identify the effects on the bat fauna of historical logging practices. Overall, 12 sites were sampled (four sites for each forest type) with bat activity and vegetation structure conducted on-track and off-track at each site and insect abundance sampled only at off-track sites.
Secondly, because roosts are an important resource for bats, and may be a limiting factor in modified landscapes, we investigated the roosting requirements of two sympatric species of jarrah forest-dwelling vespertilionid bats, the Southern forest bat Vespadelus regulus and Gould‘s long-eared bat Nyctophilus gouldi. Their sensitivity to the loss of roost sites from logging and the effectiveness of current management practices at conserving appropriate roost sites were examined. As part of the research, tree (age, size, type, condition, presence of hollows, loose bark) and landscape characteristics (elevation, logging history, distance to water holes and creeklines, etc) of roosting sites were compared with random trees and their surrounding forest structure at local roost tree and broader landscape scales to determine whether bats selected roost trees and sites with particular characteristics.
The fieldwork was carried out during 2007 – 2009 and information was gathered through capture, radiotelemetry and passive monitoring using echolocation call detectors. Specifically, harp traps and radiotelemetry were used for roost-selection studies while Anabat bat detectors were used to assess bat activity (commuting, foraging) among different logging histories and in response to forest structural attributes and insect activity. Light traps were used to assess insect availability in relation to bat activity and forest structure.
The activity of different bat species related in different ways to the structural vegetation parameters, generally reflecting bat echolocation ability and manoeuvrability. Bats tended to use tracks more than off-track locations, thereby avoiding clutter at off-track locations. At the same time, tracks recorded similar activity across logging histories. However, off-track activity in old regrowth was significantly greater than either young regrowth or recently logged forest. Two taxa, Vespadelus regulus and Nyctophilus spp. were more active in old regrowth than other logging histories. Similarly, V. regulus, Nyctophilus spp., Chalinolobus gouldii, C. morio and Falsistrellus mackenziei activity was significantly greater on-track than off-track, but this activity was similar on-track across forest types, suggesting bats‘ use of forest tracks was unaffected by logging. As an indication of the association of low bat activity off-track with clutter, negative relationships of under-storey clutter were the most consistent predictors of bat habitat use. Conversely, reduced clutter and abundant roost resources seemed the most likely explanations for greater activity at old regrowth sites.
There were both inter-specific similarities and differences in the selection and location of roost trees and roost sites between V. regulus and N. gouldi. Both species were highly selective, preferring old large trees (> 80 cm diameter at breast height over bark – DBHOB) at intermediate or advanced stages of decay, crown senescence and deterioration with a lower percent bark cover compared to random trees. Both species also selected hollows for roosting, with V. regulus roosting exclusively in hollows but a few N. gouldi also used roosts under decorticating bark, cracks and under balga (Xanthorrhoea preissii) skirts. V. regulus preferred tall trees in the canopy with roost entrances high above the ground with little surrounding vegetation while N. gouldi preferred roosting closer to the ground and in dense clutter. In general, little evidence was found of bats roosting in either shelterwood creation or gap release silvicultural treatments, although a few N. gouldi bats roosted in retained habitat, or remnant, trees in these silvicultural treatments. Only riparian buffers and structurally mature forests appeared to provide multiple alternate roosts, containing a higher density of trees with hollows required by bats for roosting. In contrast, gap release and shelterwood creation sites contained substantially lower densities of hollow bearing trees. Pockets of mature forest that were previously only lightly and selectively logged before the introduction of Ecologically Sustainable Forest Management (ESFM) were important roosting sites for bats. However, although some N. gouldi bats selected roosts in retained or remnant trees in gap release and shelterwood creation silvicultural treatments, it remains unclear if bats can successfully breed in such regrowth forests in the absence of older forest stands and this should be a priority for future studies.
This study demonstrated that unharvested buffer strips surrounding ephemeral streams, and more open mature forests, with reduced midstoreys, were important roosting habitats for bats because they provided a large pool of older and mature trees in a variety of decay classes as roost sites. With short logging rotations in the jarrah forests and with only approximately 39 % total forest area currently reserved from logging in the study area, the roosting requirements of bats may be affected negatively as the abundance of old trees with hollows, exfoliating bark and other forms of senescence may be reduced. Thus, although this study demonstrated the importance of mature forest and buffers as mitigating measures on bat roost sites, it was unclear whether the area of retained habitat is adequate for for roosting bats given the dynamics of logging regimes in the jarrah forests, and this should be a priority to address in future research.
As the only mammals capable of true flight, bats may persist in selectively logged forests. However, as this study showed, bats are specialised in their foraging and roosting requirements. Therefore, the maintenance of forest tracks and the protection, and sustained recruitment, of hollow-bearing trees are essential for the conservation of these animals in such modified landscapes. Current management practices in the jarrah forests have created a mosaic of successional stages within logged landscapes that may satisfy the foraging requirements of many bat species. This is especially true because tracks and unlogged buffers and structurally mature forest with reduced clutter provided access to post-disturbance forests such as regrowth areas. The study also demonstrated that habitat retention, as provided by adjacent streamside buffers and mature forest in the jarrah forests were important roost sites for bats, and could mitigate against logging impacts in the long term. However, retained habitat trees in logged coupes were avoided by roosting bats and further studies are required to demonstrate if these can be used effectively by viable bat populations, especially in the absence mature unlogged forest and unlogged riparian buffers nearby. In addition, further research is required to shed light on bat overwintering and maternity roost sites that are important for the survival of bat populations. In addition, a long-term study to clarify temporal/seasonal and intra-specific variation in bat distribution and roost site selection needs to be undertaken in the jarrah forests of south-western Australia to better determine if current ESFM practices are effective at maintaining bat populations in logged forests
Geographic distribution and composition of the parasite assemblage of the insectivorous bat, Miniopterus natalensis (Chiroptera: Miniopteridae), in South Africa
No full textIncludes bibliographical references.All free-living animal species have their own unique parasite assemblages. These parasites can have a significant impact on the fitness and ecology of their hosts, and through them the ecological systems in which they occur. Gaining knowledge about these parasites offers important information on the biology, systematics and phylogenies of their hosts. During this study the following were collected: flea, fly, mite, tick and helminth species from 96 Natal Long-Fingered bat (Miniopterus natalensis Smith, 1834) individuals sampled from seven localities across South Africa. This study aimed to both identify the species forming part of this parasite assemblage, and attempted to explain the distribution of the parasites and the factors influencing it
Changing the maps of urban bat distribution
No full text© 2021 The Authors. Published by Bat Conservation Trust.
The published version can be accessed at the following link on the publisher’s website: https://cdn.bats.org.uk/uploads/pdf/Resources/Bat-Groups/Accessing-journals/BritishIslandsBats_VolTwo_2021.pdf?v=1625915928Over three decades after the establishment of the Birmingham and Black Country Bat
Group, the results of just a few years of targeted advanced surveys at woodland sites in the
green belt of the county have begun to challenge the misconceptions of bat assemblages in
urban areas. The data from the Urban Bat Project have altered the distribution maps of
species previously thought to be 'rare', 'very rare' or 'locally extinct' in the county. The
rediscovery of Brandt's bat Myotis brandti and the re-assessment of the rarity scores of nine
of the remaining 11 extant county species is likely not due to a legitimate increase in their
numbers or a broadening of their distribution. It is, rather, attributable to the increase in
recent years of higher quality acoustic monitoring devices and also to a concerted increase
in the recording of cryptic and non-ubiquitous species in a previously under-studied and
under-valued landscape
Instrumented transducer for study of the bat echolocation process
No full textEvolution has enabled the bat to echolocate with ease and efficiency, to the extent that the bats capabilities far exceed the most technologically advanced manmade systems. Such capabilities reinforce mans intrigue in the animal kingdom. In studying bats we aspire to quantify and understand their inherent skills in the hope of transferring them to engineering systems. In trying to further our understanding of the animal kingdom it is often the case that we try to replicate or mimic what the animal is doing. In terms of echolocation it is thought that a bat emits a signal and retains memory of an exact copy to be used in conjunction with the returning echo to reveal information about the target. To emulate the vocalisation and auditory system of a bat it is necessary to both accurately generate and detect sound waves
Interaction of excitation and inhibition in processing of pure tone and amplitude-modulated stimuli in the medial superior olive of the mustached bat
No full text 1. In mammals with good low-frequency hearing, the medial superior olive (MSO) processes interaural time or phase differences that are important cues for sound localization. Its cells receive excitatory projections from both cochlear nuclei and are thought to function as coincidence detectors. The response patterns of MSO neurons in most mammals are predominantly sustained. In contrast, the MSO in the mustached bat is a monaural nucleus containing neurons with phasic discharge patterns. These neurons receive projections from the contralateral anteroventral cochlear nucleus (AVCN) and the ipsilateral medial nucleus of the trapezoid body (MNTB). 2. To further investigate the role of the MSO in the bat, the responses of 252 single units in the MSO to pure tones and sinusoidal amplitude-modulated (SAM) stimuli were recorded. The results confirmed that the MSO in the mustached bat is tonotopically organized, with low frequencies in the dorsal part and high frequencies in the ventral part. The 61-kHz region is overrepresented. Most neurons tested (88%) were monaural and discharged only in response to contralateral stimuli. Their response could not be influenced by stimulation of the ipsilateral ear. 3. Only 11% of all MSO neurons were spontaneously active. In these neurons the spontaneous discharge rate was suppressed during the stimulus presentation. 4. The majority of cells (85%) responded with a phasic discharge pattern. About one-half (51%) responded with a level-independent phasic ON response. Other phasic response patterns included phasic OFF or phasic ON-OFF, depending on the stimulus frequency. Neurons with ON-OFF discharge patterns were most common in the 61-kHz region and absent in the high-frequency region. 5. Double tone experiments showed that at short intertone intervals the ON response to the second stimulus or the OFF response to the first stimulus was inhibited. 6. In neuropharmacological experiments, glycine applied to MSO neurons (n = 71) inhibited any tone-evoked response. In the presence of the glycine antagonist strychnine the response patterns changed from phasic to sustained (n = 35) and the neurons responded to both tones presented in double tone experiments independent of the intertone interval (n = 5). The effects of strychnine were reversible. 7. Twenty of 21 neurons tested with sinusoidally amplitude-modulated (SAM) signals exhibited low-pass or band-pass filter characteristics. Tests with SAM signals also revealed a weak temporal summation of inhibition in 13 of the 21 cells tested.(ABSTRACT TRUNCATED AT 400 WORDS) </jats:p
Bat response to differing fire severity in mixed-conifer forest California, USA
No full textWildlife response to natural disturbances such as fire is of conservation concern to managers, policy makers, and scientists, yet information is scant beyond a few well-studied groups (e.g., birds, small mammals). We examined the effects of wildfire severity on bats, a taxon of high conservation concern, at both the stand (<1 ha) and landscape scale in response to the 2002 McNally fire in the Sierra Nevada region of California, USA. One year after fire, we conducted surveys of echolocation activity at 14 survey locations, stratified in riparian and upland habitat, in mixed-conifer forest habitats spanning three levels of burn severity: unburned, moderate, and high. Bat activity in burned areas was either equivalent or higher than in unburned stands for all six phonic groups measured, with four groups having significantly greater activity in at least one burn severity level. Evidence of differentiation between fire severities was observed with some Myotis species having higher levels of activity in stands of high-severity burn. Larger-bodied bats, typically adapted to more open habitat, showed no response to fire. We found differential use of riparian and upland habitats among the phonic groups, yet no interaction of habitat type by fire severity was found. Extent of high-severity fire damage in the landscape had no effect on activity of bats in unburned sites suggesting no landscape effect of fire on foraging site selection and emphasizing stand-scale conditions driving bat activity. Results from this fire in mixed-conifer forests of California suggest that bats are resilient to landscape-scale fire and that some species are preferentially selecting burned areas for foraging, perhaps facilitated by reduced clutter and increased post-fire availability of prey and roost
Bat eyes have ultraviolet-sensitive cone photoreceptors
No full textMammalian retinae have rod photoreceptors for night vision and cone photoreceptors for daylight and colour vision. For colour discrimination, most mammals possess two cone populations with two visual pigments (opsins) that have absorption maxima at short wavelengths (blue or ultraviolet light) and long wavelengths (green or red light). Microchiropteran bats, which use echolocation to navigate and forage in complete darkness, have long been considered to have pure rod retinae. Here we use opsin immunohistochemistry to show that two phyllostomid microbats, Glossophaga soricina and Carollia perspicillata, possess a significant population of cones and express two cone opsins, a shortwave-sensitive (S) opsin and a longwave-sensitive (L) opsin. A substantial population of cones expresses S opsin exclusively, whereas the other cones mostly coexpress L and S opsin. S opsin gene analysis suggests ultraviolet (UV, wavelengths <400 nm) sensitivity, and corneal electroretinogram recordings reveal an elevated sensitivity to UV light which is mediated by an S cone visual pigment. Therefore bats have retained the ancestral UV tuning of the S cone pigment. We conclude that bats have the prerequisite for daylight vision, dichromatic colour vision, and UV vision. For bats, the UV-sensitive cones may be advantageous for visual orientation at twilight, predator avoidance, and detection of UV-reflecting flowers for those that feed on nectar
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