Search

We recorded social vocalizations from two sympatric species of glossophagine bats, Glossophaga soricina and G. commissarisi, using habituated captive groups that were housed in separate flight cages. Whenever possible, the species-specific vocalization types were described in the light of the social context in which they were produced. Several vocalization types within each species’ repertoire had remarkable similarities to vocalization types in the other species’ repertoire. Out of these, four vocalization types with interspecific acoustic similarities (approach pulses, distress calls, aggressive trills, and alert calls) were used in similar behavioral contexts in both species. Approach pulses were produced whenever a bat was flying towards an already occupied roost. Distress calls were uttered whenever a bat was attacked by conspecifics or restrained by the observer, whereas aggressive trills were produced during aggressive encounters prior to physical contact. Alert calls were uttered when bats were disturbed or when several individuals were circling the same location. The interspecific similarity of both the social context and the acoustic structure of vocalization types suggest that the potential for interspecific communication is high in G. soricina and G. commissarisi.

In males of the grasshopper Chorthippus biguttulus the relationship between song and mating success was investigated in three isolated field populations of individually marked animals within their natural habitat. In a population with muted males (forewings removed), females mated on average 1.7 days later than in a population with intact males. But approximately 14 days after the imaginal moult, roughly corresponding with the time of the first oviposition, 100% of females in both populations had mated. In a further test population, females with a choice between singing and mute males mated almost exclusively (16 from 17 observed copulations) with the intact, singing males. The chance encounter frequency of a male and female was equally high for all populations (on average one encounter every 1.2 h). Different encounter probabilities cannot therefore have caused either mating delay in the population with muted males or preferential selection of intact partners.

Most bat species inhabit roosting sites in whichthey are well concealed during the day, such ascaves or tree holes, whereas others roost in exposedlocations on tree trunks or branches (Kunz and Lum -sden, 2003). For the latter, it is essential to appearcryptic in order to avoid predation or disturbance atthe day-roost. Several traits have evolved to enhancethe bats’ cryptic appearance, including cryptic col-oration (e.g., the greenish wings of the foliage-roost-ing bat

Like many other mammals, Saccopteryx bilineata exhibits a polygynous mating system, in which each male defends a group of females called a harem. Colonies consist of several harems, and nonharem males roost adjacent to harems. Unlike most other mammals, females disperse from their natal colony and most juvenile males remain in it. Thus, colonies consist of patrilines, which promotes intense local mate competition. Females are in estrus during a few weeks at the end of the rainy season. Mating is most likely initiated by females and preceded by intense courtship displays of males. Forty percent of colony males do not sire any offspring during their tenure in the colony, whereas a few males can sire up to 6 offspring in a single year. Males use olfactory, visual, and acoustic signals for courtship, and they demonstrate territory ownership by scent marks, lowfrequency calls, and visual displays. Harem males sire on average more offspring than do nonharem males but produce only 30% of the offspring within their own harem territory, with 70% being sired by other harem males or nonharem males. Reproductive success of males increases with decreasing size, fluctuating asymmetry, and fundamental frequency of territorial calls. In addition, females that are closely related to the harem holder are more likely to mate with other males than with the harem holder. Sexual selection in S. bilineata is most likely influenced by intense local mate competition caused by scarce roosts and the patrilineal organization of colonies.

In many animal species, individuals compete for resources but avoid escalated conflicts by threat displays, i.e. a mutual signalling behaviour that enables the opponents to predict the outcome of the conflict without the necessity of actual fighting. For example, territory holders may use acoustic signals to communicate not only their own identity and the borders of their territory but also their competitive quality, fighting ability and motivation. Here, we show that male sac-winged bats, Saccopteryx bilineata, adjust their vocal territorial displays according to the fundamental frequency of territorial songs of their opponents. In playback experiments with territorial males, low-frequency stimuli elicited a higher territorial song rate and length than high-frequency stimuli. Male S. bilineata that sing more often and with lower fundamental frequencies have been shown to sire more offspring than their competitors. Fundamental frequency of territorial songs, hence, may reveal male quality and, consequently, the resulting threat posed to competing males. We argue that this is reflected in the increased response of competitors to low-frequency territorial songs shown here. Such competitive signalling behaviour has been shown in a few mammal species like red deer and baboons but, thus far, not in bats.

In the Neotropics ongoing deforestation is producing open and heavily fragmented landscapes dominated by agriculture, mostly plantations and cattle pastures. After some time agriculture often becomes uneconomical and land is abandoned. Subsequent habitat regeneration may be slow because seed inputs are restricted by a lack of incentives--such as suitable roost sites--for seed dispersers to enter deforested areas. Increasing environmental awareness has fostered growing efforts to promote reforestation. Practical and cost-efficient methods for kick-starting forest regeneration are, however, lacking. We investigated whether artificial bat roosts for frugivorous bat species can attract these key seed dispersers to deforested areas, thereby increasing seed rain. We installed artificial bat roosts in a forest-pasture mosaic in the Costa Rican Atlantic lowlands and monitored bat colonization and seed dispersal. Colonization occurred within a few weeks of installation, and 10 species of bats occupied the artificial roosts. Five species of frugivorous or nectarivorous bats colonized artificial roosts permanently in both primary habitat and in deforested areas, in numbers similar to those found in natural roosts. Seed input around artificial roosts increased significantly. Sixty-nine different seed types, mostly of early-successional plant species, were transported by bats to artificial roosts in disturbed habitats. The installation of artificial bat roosts thus successfully attracted frugivorous bats and increased seed inputs into degraded sites. This method is likely to speed up early-vegetation succession, which in turn will attract additional seed dispersers, such as birds, and provide a microhabitat for seeds of mid- and late-successional plants. As well as supporting natural forest regeneration and bat conservation, this cost-efficient method can also increase environmental awareness among landowners.

Since its description in 2001 Alcathoe's myotis (Myotis alcathoe) was recorded from several locations across Europe. Here we describe the first records of this species from Germany, Poland, Albania, and from the European part of Turkey, including the northernmost locality in central Germany (51°23′N, 11°01′E). Compilation of all up-to-date records shows that M. alcathoe has a wide European distribution although it seems to be rare at most places. The habitats where the bat was recorded are natural, moist and deciduous forests with old trees and water streams as can be found, for example, in canyons or forests of alluvial origin. Such habitats suggest that the species probably has a more continuous and wider distribution than currently known and might be expected to occur even further to the North.

Neotropical nectar-feeding bats (Glossophaginae) are highly specialized in the exploitation of floral nectar and have one of the highest mass-specific metabolic rates among mammals. Nevertheless, they are distributed throughout the tropics and subtropics over a wide elevational range, and thus encounter many extreme and energetically challenging environmental conditions. Depressing their otherwise high metabolic rate, e.g., in situations of food restriction, might be an important adaptive physiological strategy in these dietary specialists. We investigated the thermoregulatory behavior of captive 10-g nectar feeding bats (Glossophaga soricina; Chiroptera, Phyllostomidae) under variable ambient temperatures (T a) and feeding regimes and predicted that bats would use torpor as an energy-conserving behavior under energetic constraints. All tested animals entered torpor in response to energetic restrictions and the depth of torpor was dependent on the body condition of the animals and hence on their degree of physiological constraints. Periods of torpor with body temperatures (T b) below 34°C were precisely adjusted to the photoperiod. The median length of diurnal torpor was 11.43 h. The lowest T b measured was 21°C at a T a of 19°C. Estimated energy savings due to torpor were considerable, with reductions in metabolic rate to as low as 5% of the metabolic rate of normothermic bats at the same T a. However, contrary to temperate zone bats that also employ diurnal torpor, G. soricina regulated their T b to the highest possible levels given the present energetic supplies. To summarize, G. soricina is a precise thermoregulator, which strategically employs thermoregulatory behavior in order to decrease its energy expenditure when under energetic restrictions. This adaptation may play a crucial role in the distribution and the assembly of communities of nectar-feeding bats and may point to a general capacity for torpor in tropical bats.

The songflight and the territorial behaviour of courting male pipistrelles (Pipistrellus pipistrellus) were observed in an urban habitat of this bat species, in the city of Bayreuth in Bavaria. (1) Within the city limits, from the middle of July to the end of October but most intensively in September, the male bats occupied courtship territories averaging about 200 m in diameter. At night they patrolled these territories along regular flight routes emitting characteristic advertisement calls. By day they sheltered in crevices in buildings. (2) The courtship territories were densely distributed in the center of the inner city and rarer at the outskirts. As all known larger winter roosts as well as the ‘invasion centers’ (typical late summer swarming sites of this species) also were in the inner city, territories were situated around winter quarters, but not in the vicinity of the nursery roosts, which were lying at the edge of the city and outside it. (3) The males evidently arrange their courtship territories in such a way that as many females as possible pass through them when they inspect the winter roosts. That is, they are not defending resources important to the females; instead, they position their courtship territories near the resources the females require. As male territories are densely packed, the males offer a possibility for mate choice to the females, so that the mating system also bears some likeness to a lek.

We report bat visits to the inflorescences of Marcgravia pittieri. The animals were videotaped visiting the nectaries of the inflorescences in short hovering flight. Nectarivorous bats caught in front of the inflorescences were Anoura cultrata and Hylonycteris underwoodi (both Phyllostomidae: Glossophaginae). Furthermore, we provide a short overview on inflorescence architecture within the genus Marcgravia with a special focus on functional morphology in chiropterophilous species.

Chorthippus lacustris is an endemic grasshopper (Orthoptera) species in Epirus, Greece. Its population status, habitat characteristics, and relation to historical and current human land use are investigated. The species has a restricted and fragmented distribution pattern. Five locations, four within Pamvotida Lake basin and one in Lake Paramythia, cover a total of 0.12 km2. It is strongly dependent on wet grasslands, flooded on a seasonal basis. The greatest population density is recorded in the site with the greatest diversity of dominant plant species. Ch. lacustris is estimated to have lost 85–99% of its habitat during the last 50 years due to wetland drainage. The main threat to the species survival is further habitat loss by urbanisation around Pamvotida Lake and by land conversion to agriculture in Paramythia Lake, even though both sites belong to the Natura 2000 network. The species status is Critically Endangered and it should be listed in Annex II of the Habitat Directive (92/43/EEC) as a priority species for conservation. Restoring wet grasslands, protecting them from further urbanisation and drainage, and monitoring species population are the main measures proposed for its conservation.

We studied the echolocation calls emitted by Phyllops falcatus (Chiroptera: Phyllostomidae) during foraging, in the field and in the lab. Calls emitted in free flight, in a more or less uncluttered situation, were about 4.5 ms (up to 5.3 ms) long and characterized by a sweep of the first harmonic (= fundamental) from ca. 73 kHz down to about 23 kHz, which is unusually large for phyllostomid bats. A less intense second harmonic was always present. The intervals between pulses varied between 55 and 170 ms with a mean of about 110 ms. During approach to bushes or trees (or during flight in confined space between bushes), or in the flight room, calls became shorter (ca. 2 ms) and more energy was allocated to the second harmonic, sometimes also a third harmonic appeared. During approach to a fruit calls were further shortened (about 1 ms or less), and call frequency increased to about 5 calls/100 ms, calls often being grouped. The large bandwidth of the first harmonic separates Phyllops from all other Cuban bat species and allows identification in the field.

Vocalisations of many songbirds, anurans, and insects are shaped by sexual selection. Males acoustically compete for territories, and females choose their mates by means of male courtship songs. In courtship, richness and complexity of elements are often favoured characters. Only a few examples of complex songs are known in mammals. Males of the harem-polygynous sac-winged bat (Saccopteryx bilineata, Emballonuridae) have an uncommonly complex vocal repertoire, and different song types of males are used in the context of territorial defence and in courting females. We classified the daytime vocalisations of 16 male S. bilineata from a colony in Costa Rica, both on the basis of their acoustical properties and the social context in which they occurred. Seven vocalisation types were differentiated: echolocation pulses, barks, chatter, whistles, screeches, territorial songs and courtship songs. Territorial songs were short, rather stereotyped and not obviously directed towards a certain conspecific. They appear to be of importance in male competition for harem territories, in which females roost during the day. Courtship songs were exclusively observed when males displayed towards a female; they were long and complex, and consisted of highly variable elements (“calls”). We classified the calls in courtship songs of six males into call types, based on acoustical properties, mainly spectral purity and duration. Four call types are described in detail: trills, noise-bursts, “short tonal” calls, and “quasi constant frequency” calls. Twelve parameter values were extracted from the most common call type, the trill. Discriminant function analysis of trills showed that different males had different repertoires. This could allow females to use trill parameters for recognition of individual males and thus for mate choice.

Glossophagine bats (Phyllostomidae, Glossophaginae) are specialized visitors to the flowers of several hundred species of neotropical plants. They are able to exploit flowers in hovering flight by imbibing nectar with a highly protrusile brush-tip tongue. As tongue extension is achieved by muscular and vasohydraulic mechanisms, its operational length can be inferred only from actively feeding animals. For this study, we measured maximum tongue extensions during nectar feeding in 9 species of glossophagine bats. We trained bats to feed from vertically oriented glass test tubes (9- and 15-mm inside diameter). The maximum depth of nectar drainage by a bat was recorded as maximum operational tongue length. Measured operational tongue lengths were in the range of the total body length of bats. The record length was 77 mm (in tubes with 15-mm inside diameter) in the 17-g flower specialist Choeronycteris mexicana. This compares with only 11–24 mm in the nonglossophagine frugivorous bat Carollia perspici...

SUMMARY Nectar-feeding glossophagine bats searching for flowers are guided by their echolocation system as well as olfactory cues in detecting and recognizing nectar sources. Therefore, chiropterophilous plants, which depend on these bats as pollinators, may be expected to have evolved acoustically conspicuous flowers that facilitate detection. As it is poorly understood how bats manage to find and recognize flowers acoustically, we investigated the echoes of some of the flowers pollinated by bats. Echoes of bell-shaped bat-pollinated flowers have characteristic features with respect to the echoes they reflect to a calling bat and differ from the echoes of leaves or other objects in their surroundings: the echoes are comparatively long and of complex spectral composition. Owing to the specific shape of the flowers, characteristic `spectral directional patterns' result when the spectra of the echoes are plotted against the angle of sound incidence. We suggest that bats are able to recognize such flowers — and probably other objects as well — not only by a characteristic spectral composition of the echo but also by comparing sequential echoes, at the same time taking into account their exact calling position relative to the object.

We analysed the polygynous mating system of the bat Saccopteryx bilineata using behaviour observations and genetic data on 11 microsatellite DNA loci. Basic social units in S. bilineata are harem groups that consist of single males and up to eight females. Colonies comprise several harem groups, and the composition of colonies and harems is often stable over several reproductive seasons. The combination of parentage exclusion and likelihood-based parentage assignment in this study produced detailed parentage information for a large colony of S. bilineata. Reproduction occurred mostly within the colony (17% extra-colony paternity), but social associations in harems within the colony did not represent reproductive units (70% extra-harem paternity). The latter finding was consistent over three reproductive seasons. Spatial association of the roosting sites of males and females could not explain parentage patterns in the colony. Even though intra-harem paternity was less frequent than expected, it contributed significantly to reproduction of harem males. On average, the number of offspring sired by a male with females in his harem territory increased significantly with harem size, which corresponds to the higher energetic investment that is related to the maintenance of large harems. However, extra-harem paternity was not correlated with a male's harem size or intra-harem reproductive success. This suggests that individual preferences of females rather than male traits associated with the ability to defend large harems are most likely to cause the detected differences between social association and genetic mating system.

Alternative tactics in reproductive behavior enable individuals to maximize their fitness in relation to competitors in the same population. In many taxa, territoriality is a common tactic of males to increase their reproductive success. In the bat Saccopteryx bilineata, territorial males defend roosting areas for females against other males and court females throughout the year. Peripheral males in the same colonies do not defend territories but compete with territorial males for reproduction with females. In this study, we monitored the behavior of the males in a natural colony over three reproductive seasons. We compared morphological and age data and measured the reproductive output of males adopting the territorial or peripheral tactic. No differences in body size or weight were detected between male types, but the probability of adopting a tactic seemed to be age dependent. Peripherals were often young males and replaced territorials in several cases, whereas the opposite case was not observed. Peripherals were not excluded from reproduction, but territorials were more likely to reproduce. Variation in reproductive success was high within both male tactics, and the reproductive success of some peripherals was comparable to territorials, but, on average, the reproductive success of territorials was more than twice as high. Therefore, behavioral tactics do not seem to be equally profitable in general but may represent different phases in the reproductive life of many S. bilineata males. Copyright 2002.

Saccopteryx bilineata has a polygynous mating system in which males defend females in a harem territory. Harem defense and courtship include energetically costly flight maneuvers and hovering displays. We tested if (1) harem males have a greater field metabolic rate than non-harem males or females and if (2) the field metabolic rate of harem males is correlated with the number of females in a harem territory. We measured the energy budget in 32 S. bilineata with the doubly labeled water method and compared these estimates with behavioral observations in the daytime roost. Among adult bats, field metabolic rate varied with body mass by an exponent of approximately two. We found no significant difference in field metabolic rate or mass-specific field metabolic rate between harem and non-harem males. The mass-specific field metabolic rate of harem-males increased with harem size. The latter finding supports the hypothesis that the energy costs of courtship display and territorial defense influence the energy budget of harem males. Overall, field metabolic rates of S. bilineata were lower than those of similarly sized bats of the temperate zone and only 2.3 times above the basal metabolic rate recorded for this species. We suggest that male S. bilineata did not take advantage of their metabolic capacity because a prudent allocation of energy to activities of harem maintenance is an adaptive strategy for males in this mating system.

We studied the interaction between the bromeliad Werauhia gladioliflora and its flower visitors in the Caribbean lowland forest of Costa Rica, in order to quantify the mutual benefits to both partners. Over 6 y, the bromeliads flowered mainly between October and December; with an individual inflorescence flowering for an average of 34 d (n = 233 inflorescences). The bromeliad showed a flexible breeding system with autogamy occurring in addition to cross-pollination. Exclusive pollinators were small nectar-feeding bats (Phyllostomidae: Glossophaginae). The average volume of nectar produced per flower was 1.1 ml (n = 25 flowers). The main visitor was the bat Glossophaga commissarisi, which approached the flowers exclusively using hovering flight. Visitation by bats, measured by infrared light sensors, occurred throughout the night with an activity peak after midnight. Median hovering duration of the bats at the flowers was 320 ms (n = 1246 visits). Hourly mean of hovering duration was negatively correlated with hourly nectar secretion rate. The flower visitation behaviour of a bat over the night seems to be shaped by a combination of intrinsic physiological factors and by nectar availability. Size of both flowers and visitors make Werauhia gladioliflora a very accessible system for quantification of factors affecting evolution of bat–plant interactions.

1. Chorthippus dorsatus, Ch. dichrous and Ch. loratus are closely related, sympatric grasshopper species (subfam. Gomphocerinae) with few morphological differences. 2. Songs of males contain two elements: pulsed syllables produced during synchronous movements of the hindlegs (part A) and ongoing noise produced during alternating movements of the hindlegs (part B). Part A predominates in songs of Ch. loratus and part B in songs of Ch. dichrous. In Ch. dorsatus both parts contribute nearly equally to the songs. 3. Ch. dichrous and Ch. loratus are Eastern species, while Ch. dorsatus occurs all over Europe including Spain and Italy. The songs of different populations of Ch. dorsatus in Europe are compared. 4. Female stridulation of the three species is similar to male stridulation. 5. Females prefer—expressed by their response songs—the conspecific signals over heterospecific ones. Discrimination, however, is not perfect. 6. Tested with artificial song models, females of the different species differ ...

The Chorthippus biguttulus group distributed in the west Palaearctic, while intensively examined in Europe, is poorly known in the glacial refugia such as Anatolia. This produces constraints in making accurate statements about evolution and the biogeography of the group. The C. brunneus subgroup of this lineage is examined using large amounts of morphological and song data from Anatolia (Asian Turkey) and representatives from Europe. Song and morphology in combination suggested three species to be found in Anatolia. The first is C. bornhalmi Harz which is also known from south-east Europe. The other two are new species: Chorthippus antecessor sp. n. and Chorthippus relicticus sp. n.. Morphologically, C. antecessor sp. n. is the most aberrant species of the C. brunneus subgroup, but is similar to C. bornhalmi in song. The specific song and morphology (the aberrant number of stridulatory pegs) define C. relicticus as a new species and both also indicate that it is closely related to C. brunneus and C. jacobsi. A song and morphology based phyloylogenetic assumption for C. brunneus subgroup suggests C. antecessor, C. bornhalmi and C. miramae to constitute one clade and C. brunneus, C. jacobsi and C. relicticus another. The scenario suggested for their evolution assume the following steps: (i) divergence of C. bornhalmi from a C. antecessor like ancestor, (ii) derivation of an ancestral population (which later give rise to C. brunneus + C. jacobsi + C. relicticus) from a C. bornhalmi like ancestor, and (iii) later fragmentation of this ancestral population to result in the present three species (C. brunneus + C. jacobsi + C. relicticus). All of these events seem to be correlated with the climatic cycles during Pleistocene. The conclusion is that the two new species are range-restricted, vulnerable species as is the case for many other taxa present in the Mediterranean Taurus biodiversity hotspot.

SUMMARY Nectar feeding bats use echolocation to find their flowers in the dense growth of tropical rainforests, and such flowers have evolved acoustic features that make their echo more conspicuous to their pollinators. To shed light on the sensory and cognitive basis of echoacoustic object recognition we conducted a size discrimination experiment with the nectarivorous bat Glossophaga soricina and compared the bats' behavioural performance with the echoic features of the training objects. We chose a simple geometric form, the hollow hemisphere, as the training object because of its resemblance to the bell-shaped concave form of many bat flowers, as well as its special acoustic qualities. The hemispheres showed a characteristic echo pattern, which was constant over a wide range of angles of sound incidence. We found systematic size-dependent changes in the echo's temporal and spectral pattern as well as in amplitude. Bats were simultaneously confronted with seven different sizes of hollow hemispheres presented from their concave sides. Visits to one particular size were rewarded with sugar water, while we recorded the frequency of visits to the unrewarded hemispheres. We found that: (1) bats learned to discriminate between hemispheres of different size with ease; (2) the minimum size difference for discrimination was a constant percentage of the hemisphere's size (Weber fraction: approximately 16% of the radius); (3) the comparison of behavioural data and impulse response measurements of the objects' echoes yielded discrimination thresholds for mean intensity differences (1.3 dB), the temporal pattern (3-22 μs) and the change of spectral notch frequency(approximately 16%). We discuss the advantages of discrimination in the frequency and/or time domain.

The habitat preferences and activity of greater mouse-eared bats were investigated by means of radio-telemetry in two regions in Upper Franconia (Bavaria, Germany) that are characterized by a mosaic of deciduous forests, coniferous forests and woodless areas. In one case bats roosted in a maternity colony from which they visited foraging habitats up to 10.8 km away; in the second, the bats started in a cave which served as a night roost. These bats foraged around the cave up to 2.5 km away. Mean size of foraging areas was 13.1 ± 4.6 ha. Most of the bats used several foraging areas per night (mean 5.1, range 1–10). Hunting time per foraging site ranged from 5 to 224 (median 25) minutes. Foraging habitats in some individuals remained constant over two consecutive years. The bats hunted almost exclusively in woodland (98% of the hunting time) with a significant preference for deciduous forests as opposed to coniferous forests. The preference for deciduous forests as foraging habitats is likely to be caused b...

Several hundred species of neotropical plants are pollinated by glossophagine bats1,2. These bats use their highly developed sonar system for orientation, so we might expect bat-pollinated flowers to have evolved acoustically conspicuous structures to make them easier to detect. We find that the bat-pollinated neotropical vine Mucuna holtonii directs its echolocating pollinators to its flowers by means of an acoustic nectar guide. The flower contains a small concave ‘mirror’ that works like an optical cat's eye, but in the acoustic domain, reflecting most of the energy of the bats' echolocation calls back into the direction of incidence.

In the Constant Frequency portions of the orientation calls of various Rhinolophus and Hipposideros species, the frequency with the strongest amplitude was studied comparatively. (1) In the five European species of the genus Rhinolophus call frequencies are either species-specific (R. ferrumequinum, R. blasii and R. euryale) or they overlap (R. hipposideros and R. mehelyi). The call frequency distributions are approximately 5–9 kHz wide, thus their ranges spead less than ±5% from the mean (Fig. 1). Frequency distributions are considerably narrower within smaller geographic areas. (2) As in other bat groups, call frequencies of the Rhinolophoidea are negatively correlated with body size (Fig. 3). Regression lines for the genera Rhinolophus and Rhinolophus, species from dryer climates have on the average higher call frequencies than species from tropical rain forests. (4) The Krau Game Reserve, a still largely intact rain forest area in Malaysia, harbours at least 12 syntopic Rhinolophus and Hipposiderso species. Their call frequencies lie between 40 and 200 kHz (Fig. 2). Distribution over the available frequency range is significantly more even than could be expected from chance alone. Two different null hypotheses to test for random character distribution were derived from frequency-size-relations and by sampling species assemblages from a species pool (Monte Carlo method); both were rejected. In particular, call frequencies lying close together are avoided (Figs. 4, 5). Conversely, the distribution of size ratios complied with a corresponding null hypothesis. This even distribution may be a consequence of resource partitioning with respect to prey type. Alternatively, the importance of these calls as social signals (e.g. recognition of conspecifics) might have necessitated a communication channel partitioning.