Echolocation in the notch-eared bat,Myotis emarginatus

Summary In Myotis emarginatus, the patterns of echolocation sounds vary with different foraging habitats: In commuting flights the echolocation sounds are linearly frequency modulated sweeps that start at about 100 kHz, terminate at 40 kHz, and have a duration of 1–3 ms. They consist of a loud first harmonic. The second and third harmonics are at least 15 dB fainter than the first one and often undetectable. A distinctly different type of sound is emitted when the bats search for flying insects in open spaces. The sounds are reduced in bandwidth and elongated by a constant frequency component that follows the initial frequency modulated part. Typically, sounds start at about 94 kHz and terminate in a constant frequency component at about 40–45 kHz. The average duration of the constant frequency tail is 2.8 ms; this approximately doubles the length of the pulse, with the longest recorded sound lasting 7.2 ms. When bats are foraging near and within foliage, and gleaning prey from foliage, echolocation sounds are brief (average 1 ms) frequency modulated pulses with a broad bandwidth. The pulses start at about 105 kHz and sweep down to 25 kHz. During gleaning within a building, the frequency range of the sounds is shifted to higher frequencies and extends from 124 to 52 kHz. When the bats forage for aireal insects in a confined area that creates echo-clutter, they emit sounds similar to those used during gleaning within buildings except that sound durations are extended to about 1.8 ms. In each foraging area, the echolocation sounds emitted during the search for and approach to prey are similar in structure. Sound and pause durations are reduced in the approach phase. Irrespective of foraging style and habitat, immediately before capture the bat emits a rapid and stereotyped sequence of 2-10 echolocation pulses (final buzz). These pulses are brief (0.2–0.5 ms), frequency modulated sounds with a reduced bandwidth. The sounds start at 45 kHz and sweep down to 35–20 kHz. The repetition rate is increased up to 200 pulses/s. Offprint requests to: G. Neuweiler     

Foraging behaviour and echolocation in the rufous horseshoe bat (Rhinolophus rouxi) of Sri Lanka

Summary In October 1984 foraging areas and foraging behaviour of the rufous horseshoe bat, Rhinolophus rouxi, were studied around a nursery colony on the hill slopes of Sri Lanka. The bats only foraged in dense forest and were not found in open woodlands (Fig. 1). This strongly supports the hypothesis that detection of fluttering prey is by pure tone echolocation within or close to echo-cluttering foliage. During a first activity period after sunset for about 30–60 min, the bats mainly caught insects on the wing. This was followed by a period of inactivity for another 60–120 min. Thereafter the bats resumed foraging throughout the night. They mainly alighted on specific twigs and foraged in flycatcher style. Individual bats maintained individual foraging areas of about 20x20 m. They stayed in this area throughout the night and returned to the same area on subsequent nights. Within this area the bats generally alighted on twigs at the same spots. Foraging areas were not defended against intruders. The bats echolocated throughout the night at an average repetition rate of 9.6±1.4 sounds/s. While hanging on twigs they scanned the surrounding area for flying prey by turning their bodies continuously around their legs. On average they performed one brief catching flight every 2 min and immediately returned to one of their favourite vantage points. Echolocation sounds may consist of up to three parts, a brief initial frequency-modulated (FM) component, a long constant frequency (CF) part lasting for about 40–50 ms, and a final FM part again (Fig. 4b, c). Adult males and females emitted pure tone frequencies in separate bands, the males from 73.5–77 kHz and the females from 76.5–79 kHz (Fig. 5). During scanning for prey from vantage points, the bats mostly emitted pure tones without any FM component (Fig. 4a). The last few pure tones emitted before take-off were prolonged to about 60 ms duration. The final FM part was therefore not an obligatory component of the echolocation signals in horseshoe bats. During flight and especially during emergence from the cave, most sounds consisted of a pure tone and loud initial and final FM sweeps. We therefore suggest that the initial FM part might also be relevant for echolocation. From our observations we conclude that the FM components are especially important during obstacle avoidance. In most sounds emitted in the field a fainter first harmonic was present. It was usually up to 30 dB fainter than the second harmonic, but in some instances it was as loud or even distinctly louder than the second one (Fig. 6a). Even within one sound the intensity relationship between the two harmonics may be reversed. We therefore suggest that the first harmonic is an integral part of the signal and relevant for information analysis in echolocation.     

Echolocation,development, and vocal communication in the lesser bulldog bat,Noctilio albiventris

Summary Foraging and echolocation behavior and its ontogeny in the lesser bulldog bat, Noctilio albiventris, were studied in Panama under field and captive conditions. The vocalizations utilized for echolocation and communication were monitored. Adult N. albiventris captured insect prey from the water surface employing various combinations of CF/FM (constant frequency and frequency modulated) signals. The proportions of CF/FM and the repetition rate were a function of the bat's activity. Most adults exhibited post-sunset and pre-dawn foraging activity, although several telemetered lactating females foraged for only the half hour after dusk, spending the rest of the night with their babies in the roost. When the juveniles began to leave the roost at the age of two months, they appeared to accompany their mothers on initial flights.Captive infant Noctilio developed slowly, and did not fly until about 5–6 weeks postnatally. They continued to nurse for almost 3 months, even though they were capable of eating solid food at about 6 weeks. Previous to weaning, mothers fed their infants with masticated food from their cheekpouches.At birth, Noctilio emit a combination of long FM isolation calls and shorter CF/FM pulses. Mothers nurse only their own babies which they appear to recognize by a vocal signature contained in the infants' isolation calls. The individual isolation calls, as well as the mother's communication sounds, appear to be variations of an FM sinusoidal wave. The periodicity and amplitude change, and different portions including harmonics are added or deleted. The short CF/FM signals of the infant evolve into the adult orientation type signals as the CF component increases in frequency and the repetition rate increases. These sounds appear to serve a dual function in communication and echolocation. Mother-young pairs were observed to call antiphonally, utilizing CF/short FM signals in retrieval situations. This duetting was also observed in bats flying over the Chagras River after the time the juveniles began to fly, and may function to maintain vocal contact during initial foraging flights.Deceased     

Unusual echolocation behavior in a small molossid bat, <Emphasis Type="Italic">Molossops temminckii,</Emphasis> that forages near background clutter

When searching for flying insects, Molossops temminckii uses unusual echolocation calls characterized by upward modulation of frequency vs time (UFM). Call frequency increases asymptotically in the relatively long (∼8 ms) pulses from a starting frequency of ∼40 kHz to a long narrowband tail at ∼50 kHz. When approaching a prey, the bat progressively increases the duration of calls and intersperses in the sequence broadband downwardly frequency-modulated signals with a terminal frequency of about 53 kHz, which totally replaces the UFM signals at the end of the approach phase. The sequence progresses to a capture buzz resembling those from other molossid and vespertilionid bats. The M. temminckii wing morphology is characterized by an average aspect ratio and a high wing loading, suggesting that it is more maneuverable than the typical Molossidae but less than typical Vespertilionidae. M. temminckii regularly forages near clutter, where it needs to pay attention to the background and might face forward and backward masking of signals. We hypothesize that the UFM echolocation signals of M. temminckii represent an adaptation to foraging near background clutter in a not very maneuverable bat needing a broad attention window. The broadband component of the signal might serve for the perception of the background and the narrowband tail for detection and perhaps classification of prey. Bats may solve the signal masking problems by separating emission and echoes in the frequency domain. The echolocation behavior of M. temminckii may shed light on the evolution of the narrowband frequency analysis echolocation systems adopted by some bats foraging within clutter.     

The roles of echolocation and olfaction in two Neotropical fruit-eating bats, Carollia perspicillata and C. castanea, feeding on Piper

We studied the echolocation and foraging behavior of two Neotropical frugivorous leaf-nosed bats (Carollia perspicillata, C. castanea: Phyllostomidae) in a flight cage. To test which cues Carollia uses to detect, identify, and localize ripe Piper fruit, their preferred natural food, we conducted experiments under semi-natural conditions with ripe, unripe, and artifical fruits. We first offered the bats ripe fruits and documented their foraging behavior using multiflash stereophotography combined with simultaneous sound recordings. Both species showed a similar, stereotyped foraging pattern. In searchflight, the bats circled through the flight cage in search of a branch with ripe fruit. After finding such a branch, the bats switched to approach behavior, consisting of multiple exploration flights and the final approach when the bats picked up the fruit at its tip and tore it off in flight. Our behavioral experiments revealed that odor plays an important role in enabling Carollia to find ripe fruit. While foraging, Carollia always echolocated and produced multiharmonic, frequency-modulated (FM) signals of broad bandwidth, high frequency, short duration, and low intensity. We discriminated an orientation phase (mostly a single pulse per wingbeat) and an approach phase (groups of two to six pulses per wing beat). We conclude from the bats' behavioral reaction to real and artificial fruit as well as from characteristic patterns in their echolocation behavior that during exploration flights, Carollia changes from primarily odor-oriented detection and initial localization of ripe fruit to a primarily echo-oriented final localization of the position of the fruit. Received: 27 March 1997 / Accepted after revision: 28 February 1998     

The social organization of the common vampire bat

Summary At a site in Costa Rica, three groups of 8–12 adult female vampire bats, Desmodus rotundus, utilize group-specific sets of hollow trees as day roosts. Long-term nonrandom associations between pairs of females, as measured by the proportion of time one bat spends roosting in the same tree with another bat over a 3 year period, occur even when preferences for particular trees are removed. Significant associations exist between both related and unrelated adult females. Adult male bats, however, show few associations with females or other males. By observing bats within trees and while foraging, and by monitoring feeding flights with radiotelemetry, the following potential benefits of association could be tested. Females roost together to (1) share a suitable microclimate, (2) avoid predators, (3) avoid ectoparasite infestations, (4) minimize travel to mobile prey animals, (5) respond to coercive males, (6) feed simultaneously from a bite, (7) remove ectoparasites by allogrooming, and (8) share food by regurgitating blood to other bats within roosts. The data do not indicate that any of the first five hypotheses provide significant benefits for long-term associations although predators and ectoparasite levels may cause occasional changes in roost sites. Simultaneous feeding was uncommon and apparently confined to females and their recent offspring. Allogrooming, although common, occurred independently of the presence of ectoparasites. Food sharing, however, occurred between both related and unrelated adult females with high levels of association and provides at least one selective advantage for maintaining cohesive female groups.     

Low roost-site fidelity in pallid bats: associated factors and effect on group stability

Despite potential costs of changing roost or densites, many animals frequently move between roosts or dens. Pallid bats (Antrozous pallidus) change diurnal roost sites frequently and also reportedly have a variety of cooperative social behaviors, many of which are associated with the care of developing offspring. Roost switching is likely to increase the costs of maintaining the group stability expected with social cooperation. Pallid bats roosting in rock crevices in central Oregon were studied with radiotelemetry to (1) examine characteristics of day roosts, (2) determine what ecological factors were correlated with low roost fidelity, and (3) examine the temporal stability of roosting groups of pregnant and lactating bats. Pallid bats changed roosts an average of once every 1.4 days throughout the summer. The bats exhibited seasonal shifts in roost use, occupying roosts behind thin slabs of rock in cool weather and roosts in deep rock crevices in warm weather. Roost switching was not correlated with daily variations in weather conditions or with structural characteristics of the diurnal roosts, although switching may have allowed bats to maintain familiarity with several roosts that vary in microclimate. Roost switching was positively correlated with ectoparasite load. High ectoparasite levels were correlated with lower body weights in lactating females (Fig. 3), suggesting that parasites may be costly to the bats. Roost switching may be a strategy to decrease ectoparasite loads by interrupting the reproductive cycles of those parasites that spend at least part of their life cycle on the walls of the roost. Both pregnant and lactating pallid bats frequently changed their diurnal roost location, but lactating bats tended to travel shorter distances between consecutive roosts. Lactating bats were more likely to continue to associate with particular roostmates despite changes in the location of the diurnal roost (Fig. 4) and were less likely to roost alone. Although the stability of groups of lactating bats was not absolute, evidence supported the prediction that such groups are more cohesive than are those of pregnant bats. Received: 20 June 1995/Accepted after revision: 13 July 1996     

Relatedness structure and kin-biased foraging in the greater horseshoe bat (Rhinolophus ferrumequinum)

Female greater horseshoe bats (Rhinolophus ferrumequinum) exhibit strong natal philopatry to their maternity roost over many years, leading to the aggregation of matrilineal kin. Maternity colonies may, therefore, be expected to comprise highly related individuals, and, as such, provide conditions suitable for the evolution of kin-selected behaviours. To test these predictions, we examined relatedness and behaviour among matrilineal kin within a colony in south-west Britain. Genetic analysis of 15 matrilines, identified from microsatellite genotyping and long-term ringing surveys, revealed average relatedness levels of 0.17 to 0.64. In contrast, background relatedness among colony females approximated to zero (0.03). These results suggest that inclusive fitness benefits may only be accrued through discriminate cooperation within matrilines, and not at the wider colony level. To examine whether the potential for such benefits is realised through kin- biased cooperation during foraging, females from two matrilines were radio-tracked simultaneously over 3 years. Pairwise home-range overlap correlated significantly with Hamilton's relatedness coefficient. The greatest spatial associations were observed between females and their adult daughters, which shared both foraging grounds and night roosts, sometimes over several years. Tagged females, however, generally foraged and roosted alone, suggesting that kin-biased spatial association probably does not result from either information-transfer or cooperative territorial defence. Such patterns may instead result from a mechanism of maternal inheritance of preferred foraging and roosting sites.     

Individual specific contact calls of pallid bats (<Emphasis Type="Italic">Antrozous pallidus</Emphasis>) attract conspecifics at roosting sites

Contact calls are utilized by several bird and mammal species to maintain group cohesion and coordinate group movement. From a signal design perspective, contact calls typically exhibit acoustic features that make them easily localizable and encode information about individual or group identity. Pallid bats (Antrozous pallidus) are unusual among vespertilionids in that they often emit a loud, partially audible frequency-modulated social call several times in rapid succession while in flight. This call appears to function as a contact call in that it is frequently given when bats return from foraging and perform circular flights before entering a crevice roost. However, the degree to which pallid bats respond to the calls of conspecifics and what information is provided in the call is unknown. Thus, the goal of this study was to investigate pallid bat calling behavior to determine if calls attract roostmates or elicit responses from them and provide sufficient information for individual recognition. In playback studies, we found that contact calls, elicit calls, and approaches and that free-flying bats respond more to familiar than unfamiliar calls. In addition, analysis of frequency and temporal measurements of calls collected from multiple sites and spectral cross correlation analysis of calls recorded from the same radio-tagged bats on multiple evenings revealed that the frequency pattern of contact calls is highly repeatable over time within individuals but exhibits significant differences among individuals. Thus, contact call structure appears to be unique to individuals and stable through time, which makes these calls well-suited for roostmate recognition.     

Interindividual use of echolocation calls: Eavesdropping by bats

Summary The use of other individual's echolocation calls by little brown bats, Myotis lucifugus, was tested by observing the response of free-flying bats to presentations of recorded echolocation calls and artificial sounds. Bats responded by approaching conspecific calls while searching for food, night roosts, nursery colonies and mating/hibernation sites. Response was low or non-existant to other sounds. While searching for prey, M. lucifugus also responded to the echolocation calls of Eptesicus fuscus, a sympatric species with overlapping diet but distinctly different echolocation calls. Subadults were especially responsive to conspecific calls.All four situations in which the bats responded involve patchily distributed resources at which bats accumulate. Concentrations of echolocation calls thus likely serve as cues regarding the location of resources. Individuals approaching feeding groups, for example, could increase prey detection range by up to 50 times over individuals relying solely on their own echolocation.Although the costs associated with eavesdropping may be negligible for M. lucifugus, for other species, particularly territorial ones, being conspicuous may be a disadvantage and the possibility of being over-heard by other bats may have been one factor involved in the evolution of echolocation call design.     

The use of Doppler-shifted echoes as a flutter detection and clutter rejection system: the echolocation and feeding behavior of Hipposideros ruber (Chiroptera: Hipposideridae)

Summary Hipposideros ruber use CF/FM echolocation calls to detect the wing flutter of their insect prey. Fluttering prey were detected whether the insects were flying or sitting on a surface, and prey in either situation were captured with equal success (approximately 40% of capture attempts). Stationary prey were ignored. The bats did not use visual cues or the sounds of wing flutter to locate their prey. Wing flutter detection suggests that H. ruber exploit the Doppler-shifted information in echoes of their echolocation calls. These bats fed primarily upon moths, usually those of between 10 and 25 mm wingchord, although moths of less than 5 mm and greater than 40 mm wingchord were also attacked and captured. They showed no evidence of selecting moths on the basis of species or other taxonomic distinction, and occasionaly captured other insects.     

Social thermoregulation exerts more influence than microclimate on forest roost preferences by a cavity-dwelling bat

Nest or roost temperature (T _roost) is thought to impact reproductive fitness in many endotherms but few studies have directly tested the hypothesis that naturally occurring variability in nest or roost microclimate is large enough to affect reproductive success. We conducted a field experiment to test whether roost selection by cavity-dwelling, reproductive female big brown bats (Eptesicus fuscus) is more strongly influenced by roost microclimate or a physical characteristic of roosts that facilitates social thermoregulation (i.e., cavity volume). We quantified spatial variability in T _roost within different-sized, unoccupied cavities and also recorded T _roost in occupied vs unoccupied roost trees. We used equations relating energy use and ambient temperature for big brown bats to calculate values of daily energy expenditure from T _roost data because energy is a currency that likely affects reproductive fitness. We found no difference between maximum and minimum T _roost, spatial variability in T _roost, or predicted energy expenditure in more-preferred vs less-preferred roosts. However, there was a significant difference between T _roost and predicted energy expenditure when we compared occupied vs unoccupied roosts. The presence of bats increased T _roost by as much as 7°C, and there was a significant positive correlation between the number of bats occupying a roost, maximum daily T _roost, and energy savings. We calculate that, on average, a normothermic individual would save about 6.5 kJ/day (roughly 9% of the daily energy budget) by roosting in an occupied cavity relative to roosting alone and that savings may increase to 40 kJ/day (about 53% of the energy budget) for an individual roosting in a group of 45 bats. Our findings suggest that variability in microclimate among potential roost or nest sites may be less important to some cavity-dwelling endotherms than has been suggested in previous studies. Our results reinforce the importance of sociality and social thermoregulation to the roosting ecology of forest-living bats and socially roosting or nesting endotherms in general.     

Genetic relationships between roost-mates in a fission–fusion society of tree-roosting big brown bats (<Emphasis Type="Italic">Eptesicus fuscus</Emphasis>)

Kin-based patterns of associations are often observed in group living mammals. Colonies of forest-living big brown bats (Eptesicus fuscus) exhibit fission–fusion roosting behavior and female philopatry. Within a roosting area of forest, adult females are distributed into several subgroups roosting in different trees during the day. At night, adult females leave the roost subgroups to forage and, upon return to the roosting area at dawn, both the individual composition and location of subgroups often change. Individuals exhibit nonrandom roosting associations, and we hypothesized that genetic relationships would influence roosting associations. We determined (1) whether the strength of roosting associations between pairs of bats (based on radiotelemetry) was correlated with relatedness, (2) whether individuals that roosted together in roost subgroups were more related than by chance, and (3) from roost subgroups, the pairs of bats that roosted nonrandomly and whether the proportion of related pairs was higher than expected at random. Relatedness measures were based on microsatellite genotyping and mitochondrial DNA sequences. We found from all analyses that roosting associations were not influenced by relatedness or matrilineal relationships. These results provide clear evidence that, contrary to other mammals, kinship does not mediate roosting associations within forest living big brown bats that exhibit fission–fusion roosting behavior.     

The effect of reproductive condition on the foraging behavior of female hoary bats,Lasiurus cinereus

Summary Female mammals experience larg changes in time and energy budgets associated with reproduction and these may influence the foraging strategies of individuals. I studied the changes in foraging behavior associated with reproduction in female hoary bats, Lasiurus cinereus. As lactation progressed, individuals departed to forage earlier in the evening and spent more time foraging per night and less time roosting with their young. Foraging time increased by at least 73% between early lactation and fledging and then declined as the young became independent. Females with two young foraged for longer than did those with one and females with pre- and postfledging young foraged in different habitats. The changes in foraging time suggest that foraging activity of female L. cinereus is constrained and individuals act as time minimizers, adjusting their foraging behavior to meet current energy demand. Predation risk is unlikely to constrain the behavior of these bats. However, maximizing energy intake throughout lactation may not be the optimal strategy because storing excess energy increases flight cost and may reduce foraging efficiency. The need to keep newborn young warm may also influence foraging time. Such constraints, causing changes in foraging activity, may alter the availability of habitats and prey and must be considered when modelling foraging strategies. In addition, changes in flight time may significantly alter the energy budgets of bats in different stages of reproduction.     

Echolocation in two very small bats from Thailand Craseonycteris thonglongyai and Myotis siligorensis

Summary The echolocation and hunting behavior of two very small bats, Craseonycteris thonglongyai (Hill) and Myotis siligorensis (Horsfield), from Thailand, were investigated using multiflash photographs, video, and high-speed tape recordings with a microphone array that allowed determination of distance and direction to the bats. C. thonglongyai is the world's smallest mammal and M. siligorensis is only slightly larger. Both bats hunted insects in open areas. The search signals of C. thonglongyai were 3.5 ms long multiharmonic constant frequency (CF) signals with a prominent second harmonic at 73 kHz repeated at around 22 Hz. The band width (BW) of the short terminal frequency modulated (FM) sweep increased during the very short approach phase. In the final buzz the CF component disappeared, the duration decreased to 0.2 ms, and the repetition rate increased to 215 Hz (Figs. 2, 3, 4). There was no drop in frequency in the buzz. The video recordings of C. thonglongyai indicated that it seizes insects directly with the mouth (Fig. 1). M. siligorensis produced 5.4 ms long CF search signals at 66 kHz. The repetition rate was around 13 Hz. In the approach phase an initial broad band FM sweep was added. The buzz consisted of two phases, buzz I and buzz II. Buzz 11 was characterized by short cry durations (around 0.3 ms), a constant high repetition rate (185 Hz), a distinct drop in frequency, and a prominent second harmonic (Figs. 5, 6, 7). The drop in frequency, apparently typical of vespertilionid bats, has been explained by physiological limitations in sound production. However, C. thonglongyai produced very short signals at very high repetition rates without any frequency drop. The drop may be of adaptive value since it enables M. siligorensis to produce very short signals with high sweep rates. The drop moves the pronounced second harmonic into the frequency range of most interest to the bat (Fig. 7D). The sweep rate in this frequency range may now increase to twice the maximum rate that the vocal cords can produce directly. C. thonglongyai and M. siligorensis belong to different superfamilies, Emballonuroidea and Vespertilionoidea, respectively. In spite of their phylogenetic distance they produce strikingly similar search signals of narrow BW around 70 kHz with high source levels (100–115 dB peSPL peak equivalent sound pressure level). We argue that the signal resemblance is due to the similarity in size and hunting behavior of the two bats both hunting insects in open areas. High frequencies are heavily attenuated in air, but because of their small size the bats are restricted to hunting small insects which only reflect echoes at high frequencies. Thus, the emitted frequency is probably the lowest possible given the prey size. Hence, the two bats can only maximize the range of their sonar by decreasing the BW and emitting high intensities. Correspondence to: A. Surlykke     

Foraging habitat and echolocation behaviour of Schneider's leafnosed bat, Hipposideros speoris, in a vegetation mosaic in Sri Lanka

The Hipposideridae and Rhinolophidae are closely related families of bats that have similar echolocation (long-duration pure-tone signal, high duty cycle) and auditory systems (Doppler-shift compensation, auditory fovea). Rhinolophid bats are known to forage in highly cluttered areas where they capture fluttering insects, whereas the foraging habitat of hipposiderid bats is not well understood. Compared to rhinolophids, hipposiderid calls are shorter in duration, have lower duty cycles, and they exhibit only partial Doppler-shift compensation. These differences suggest that the foraging habitat of the two families may also differ. We tested this hypothesis by studying foraging and echolocation of Hipposideros speoris at a site with a range of vegetation types. Bats foraged only while in flight and used all available closed and edge habitats, including areas adjacent to open space. Levels of clutter were high in forest and moderate in other foraging areas. Prey capture (n=42) occurred in edge vegetation where it bordered open space. Echolocation signals of H. speoris lacked an initial upward frequency-modulated sweep and were of moderate duration (5.1-8.7 ms). Sequences had high duty cycles (23-41%) and very high pulse repetition rates (22.8-60.6 Hz). Variation in signal parameters during search phase flight across foraging habitats was low. H. speoris showed a greater flexibility in its use of foraging habitat than is known for any rhinolophid species. Our study confirmed that there are differences in habitat use between hipposiderid and rhinolophid bats and we suggest that this divergence is a consequence of differences in their echolocation and auditory systems.     

Contrasting home-range size and spatial partitioning in cryptic and sympatric pipistrelle bats

The extent of spatial partitioning in insectivorous bats, whose prey is patchily distributed and transient in nature, remains a contentious issue. The recent separation of a common Palaearctic bat, the pipistrelle, into Pipistrellus pipistrellus and Pipistrellus pygmaeus, which are morphologically similar and sympatric, provides an opportunity to examine this question. The present study used radio telemetry to address the spatial distribution and foraging characteristics of P. pipistrellus and P. pygmaeus in northeast Scotland, to test the hypothesis that coexistence between these species is facilitated through spatial segregation. We reveal large and significant differences in the spatial distribution and foraging characteristics of these two cryptic species. Individual P. pipistrellus home ranges were on average three times as large as that of P. pygmaeus, and they foraged for approximately an hour longer each night. Inter-specific spatial overlap was minimal (<5%) and core foraging areas of either species were essentially mutually exclusive despite the proximity of the two roosts. Inter-specific differences in range size were associated with the spatial dispersion of productive foraging sites within individual foraging ranges. P. pipistrellus foraging sites were highly dispersed, necessitating larger ranges. It is predicted that the spatial segregation revealed by the present study is a result of selection favouring the avoidance of competition in these species through differential habitat use.     

Echolocation behavior of the bat <Emphasis Type="Italic">Vespertilio murinus</Emphasis> reveals the border between the habitat types “edge” and “open space”

We test the hypothesis that echolocation behavior can be used to find the border between bat habitats. Assuming that bats react to background targets in “edge space” but not in “open space”, we determined the border between these two habitat types for commuting individuals of the parti-colored bat Vespertilio murinus. We recorded sequences of bats’ echolocation signals while they flew parallel to the walls of large buildings and to the ground and determined the signals’ average bandwidth, duration, and pulse interval. These parameters varied systematically with the estimated horizontal and vertical distances between the bats and the background. A distinct effect of horizontal distance to the background on echolocation behavior was found for horizontal distances of less than 6 m, thus indicating the border between edge and open space. Only a few bats flew at vertical distances below 5 m. However, enough passages at vertical distances of 5 m and above indicated that the vertical border is somewhere below a distance of 5 m. Within edge space, V. murinus reacted to the background by reducing signal duration, increasing bandwidth at closer distances, and often emitting one signal per wing beat. In open space, signal parameters did not vary as a function of distance to the background. There, V. murinus emitted the longest signals with the narrowest bandwidth and often made one or two wing beats without emitting a pulse. With our data we support with statistical methods the hypothesis that echolocation behavior reveals the border between the habitat types “edge” and “open space”.     

Ground gleaning in horseshoe bats: comparative evidence from<Emphasis Type="Italic"> Rhinolophus blasii</Emphasis>,<Emphasis Type="Italic"> R. euryale</Emphasis> and<Emphasis Type="Italic"> R. mehelyi</Emphasis>

The 71 species of horseshoe bat (genus Rhinolophus) use echolocation calls with long constant-frequency (CF) components to detect and localize fluttering insects which they seize in aerial captures or glean from foliage. Here we describe ground-gleaning as an additional prey-capture strategy for horseshoe bats. This study presents the first record and experimental evidence for ground-gleaning in the little-studied Blasius horseshoe bat (Rhinolophus blasii). The gleaning bouts in a flight tent included landing, quadrupedal walking and take-off from the ground. The bats emitted echolocation calls continuously during all phases of prey capture. Both spontaneously and in a choice experiment, all six individuals attacked only fluttering insects and never motionless prey. These data suggest that R. blasii performs ground-gleaning largely by relying on the same prey-detection strategy and echolocation behaviour that it and other horseshoe bats use for aerial hawking.We also studied the Mediterranean horseshoe bat (R. euryale) in the flight tent. All four individuals never gleaned prey from the ground, though they appeared to be well able to detect fluttering moths on the ground. It is not known yet whether ground-gleaning plays a role in Mehelys horseshoe bat (R. mehelyi). In a performance test, we measured the ability of these three European species of middle-sized horseshoe bats (R. euryale, R. mehelyi and R. blasii) to take-off from the ground. All were able to take flight even in a confined space; i.e. the willingness to ground-glean in R. blasii is not related to a superior take-off performance. In contrast to ground-gleaning bats of other phylogenetic lineages, R. blasii appears not to be a specialist, but rather shows a remarkable behavioural flexibility in prey-capture strategies and abilities. We suggest that the key innovation of CF echolocation paired with behavioural flexibility in foraging strategies might explain the evolutionary success of Rhinolophus as the second largest genus of bat.Communicated by T. Czeschlik