The food habits of a Malagasy Giant: Hipposideros commersoni (E. Geoffroy, 1813)

Hipposideros commersoni is a large microchiropteran bat endemic to Madagascar. We analysed fragments of its prey from faeces and from underneath feeding perches to describe its diet from four sites. Diet was similar across sites and Coleoptera was the main prey item by percentage volume (75%), followed by Hemiptera (13%). Carabidae and Scarabidae were the most frequent coleopterans found in the diet. Direct observations (n = 3) were made of bats flying short distances from perches along forest trails to prey on Cicadidae ( c. 20 mm in length) located on tree trunks. There were differences in the composition of faecal samples collected form netted bats and pellets collected under feeding perches, with the latter consisting of more Blattoptera (Blattellidae 'cockroaches'). Hipposideros commersoni appears to have a unique foraging behaviour and diet among Malagasy microchiropterans and its preference for certain Coleoptera and other large invertebrates may account for reported seasonal variation in body fattening and activity.     

Roosting and Foraging Behavior of Two Neotropical Gleaning Bats,Tonatia silvicola and Trachops cirrhosus (Phyllostomidae)1

We studied roosting and foraging behavior of two Neotropical gleaning bats, ?Orbigny's round-eared bat, Tonatia silvicola, and the fringe-lipped bat, Trachops cirrhosus (Phyllostomidae). Techniques included radio-tracking in a tropical lowland forest in Panama and analysis of data from long-term studies in Panama and Venezuela. Day roosts of T. silvicola were in arboreal termite nests. T. cirrhosus roosted in a hollow tree. T. silvicola emerged late (ca 60 min after sunset), and foraged close to the roosts (maximum distance 200–500 m). T. cirrhosus emerged early (ca 30 min after local sunset), and foraged farther from its roost (>1.5 km). Both bats used small foraging areas (3–12 ha) in tall, open forest. They foraged in continuous flight (maximum 27–36 min) or in short sally flights (<1 minute) from perches (“hang-and-wait” strategy). The small foraging areas of these bats and their sedentary foraging mode most likely make them vulnerable to habitat fragmentation.     

Singing strategies are linked to perch use on foraging territories in heart‐nosed bats

Acoustic communication allows animals to coordinate and optimize resource utilization in space. Cardioderma cor, the heart‐nosed bat, is one of the few species of bats known to sing during nighttime foraging. Previous research found that heart‐nosed bats react aggressively to song playback, supporting the territorial defense hypothesis of singing in this species. We further investigated the territorial defense hypothesis from an ecological standpoint, which predicts that singing should be associated with exclusive areas containing a resource, by tracking 14 individuals nightly during the dry seasons in Tanzania. We quantified the singing behavior of individuals at all perches used throughout the night. Using home range analysis tools, we quantified overall use, night ranges and singing ranges, as well as areas used in early and later time periods at night. Males sang back and forth from small (x¯ = 3.48 ± 2.71 ha), largely exclusive areas that overlapped with overall night ranges used for gleaning prey. Individuals varied in singing effort; however, all sang significantly more as night progressed. Subsequently, areas used earlier at night and overall use areas were both larger than singing areas. Individuals varied in singing strategies. Some males sang for long periods in particular trees and had smaller core areas, while others moved frequently among singing trees. The most prolific singers used more perches overall. Our results support the hypothesis that acoustic communication repertoires evolved in support of stable foraging territory advertisement and defense in some bats.     

Use of sewage treatment works as foraging sites by insectivorous bats

Sewage treatment works (STWs) with percolating filter beds are known to provide profitable foraging areas for insectivorous birds because of their association with high macroinvertebrate densities. Fly larvae developing on filter beds at STWs may similarly provide a valuable resource for foraging bats. Over the last two decades, however, there has been a decline in filter beds towards a system of 'activated sludge'. Insects and bat activity were surveyed at 30 sites in Scotland using these two different types of sewage treatment in order to assess the possible implications of these changes for foraging bats. Bat activity (number of passes) recorded from broad-band bat detectors was quantified at three points within each site. The biomass of aerial insects, sampled over the same period as the detector surveys, was measured using a suction trap. The biomass of insects and activity of Pipistrellus spp. were significantly higher at filter beds than at activated sludge sites. In addition, although foraging activity of Pipistrellus spp. at filter beds was comparable to that of adjacent 'good' foraging habitat, foraging at activated sludge sites was considerably lower. This study indicates the high potential value of an anthropogenic process to foraging bats, particularly in a landscape where their insect prey has undergone a marked decline, and suggests that the current preference for activated sludge systems is likely to reduce the value of treatment works as foraging sites for bats.     

食虫蝙蝠与昆虫之间的相互作用和协同进化关系

食虫蝙蝠与昆虫之间是捕食和被捕食的关系,夜行性昆虫是食虫蝙蝠主要的食物来源。在漫长的协同进化中,蝙蝠施加的捕食压力导致夜行性昆虫一系列特征的进化,其中一部分昆虫进化出能听到蝙蝠的超声波信号并采取逃跑行为或者能通过其它方式躲避蝙蝠,同时昆虫的适应性特征同样影响着蝙蝠的回声定位和捕食策略。本文从蝙蝠捕食昆虫的种类、昆虫对蝙蝠捕食的反应和食虫性蝙蝠对昆虫防卫的适应对策等三个方面对食虫蝙蝠与昆虫之间的相互关系进行了概述。     

Ultraviolet Radiation Influences Perch Selection by a Neotropical Poison-Dart Frog

Ambient ultraviolet-B radiation can harm amphibian eggs, larvae and adults. However, some amphibians avoid UV-B radiation when given the opportunity. The strawberry poison dart frog, Oophaga pumilio, is diurnal and males vocalize throughout the day in light gaps under forest canopies that expose them to solar radiation. Previous studies have demonstrated that males calling from high perches are more successful at mating than those at lower perches. We investigated whether frogs at higher perches receive more ultraviolet-B than those calling from lower perches. We also investigated whether frogs on perches receiving relatively low ultraviolet-B levels maintained their positions for longer compared to individuals calling from perches receiving higher levels of ultraviolet-B. Finally, since it has been hypothesized that some animals utilize levels of UV-A as a visual cue to avoid UV-B damage, we artificially elevated ultraviolet-A levels to examine whether males exposed to artificially elevated ultraviolet-A abandoned their perches sooner compared to males exposed to visible light. We found that frogs called from perches receiving low ultraviolet-B regardless of perch height, and that frogs maintain their positions longer on perches receiving low ultraviolet-B compared to perches receiving even slightly higher ultraviolet-B levels. Exposing the frogs to artificially elevated levels of ultraviolet-A radiation caused males to move off of their perches faster than when they were exposed to a control light source. These experiments suggest that ultraviolet radiation plays an important role in frog behavior related to perch selection, even in rainforests where much of the solar radiation is shielded by the forest canopy.     

食物大小对棕果蝠和犬蝠取食行为的影响

按照最优化觅食理论,动物在取食时需在能量获取与捕食风险之间权衡。本文通过室内行为实验,研究两种旧大陆果蝠棕果蝠和犬蝠对食物大小的选择规律与取食策略。按体积由小到大将苹果分为Ⅰ型、Ⅱ型、Ⅲ型、Ⅳ型4 种类型的食物块,通过红外相机观察果蝠对不同大小食块的取食情况,并就其对各类型食块的取食率、取食次数和停留时间进行统计分析。结果表明:这两种果蝠对Ⅱ型和Ⅲ型食块的取食率显著高于Ⅰ型和Ⅳ型;对Ⅰ型食块的取食次数显著高于Ⅱ型和Ⅳ型;对Ⅳ型食块的停留时间显著高于Ⅰ型和Ⅱ型。它们在摄取体积较小的食块时,以取走后进食为主要取食方式,但摄取大体积食块时则主要在原地进食。取食过程中,果蝠优先选择大小适于搬运的食块,是捕食风险与能量收益权衡的结果。     

Multimodal cues improve prey localization under complex environmental conditions

Predators often eavesdrop on sexual displays of their prey. These displays can provide multimodal cues that aid predators, but the benefits in attending to them should depend on the environmental sensory conditions under which they forage. We assessed whether bats hunting for frogs use multimodal cues to locate their prey and whether their use varies with ambient conditions. We used a robotic set-up mimicking the sexual display of a male túngara frog (Physalaemus pustulosus) to test prey assessment by fringe-lipped bats (Trachops cirrhosus). These predatory bats primarily use sound of the frog''s call to find their prey, but the bats also use echolocation cues returning from the frog''s dynamically moving vocal sac. In the first experiment, we show that multimodal cues affect attack behaviour: bats made narrower flank attack angles on multimodal trials compared with unimodal trials during which they could only rely on the sound of the frog. In the second experiment, we explored the bat''s use of prey cues in an acoustically more complex environment. Túngara frogs often form mixed-species choruses with other frogs, including the hourglass frog (Dendropsophus ebraccatus). Using a multi-speaker set-up, we tested bat approaches and attacks on the robofrog under three different levels of acoustic complexity: no calling D. ebraccatus males, two calling D. ebraccatus males and five D. ebraccatus males. We found that bats are more directional in their approach to the robofrog when more D. ebraccatus males were calling. Thus, bats seemed to benefit more from multimodal cues when confronted with increased levels of acoustic complexity in their foraging environments. Our data have important consequences for our understanding of the evolution of multimodal sexual displays as they reveal how environmental conditions can alter the natural selection pressures acting on them.     

Airport noise disturbs foraging behavior of Japanese pipistrelle bats

The expansion of anthropogenic noise poses an emerging threat to the survival and reproductive success of various organisms. Previous investigations have focused on the detrimental effects of anthropogenic noise on the foraging behavior in some terrestrial and aquatic animals. Nevertheless, the role of airport noise in impairing foraging activities of most wild animals has been neglected. Here, we aimed to assess whether foraging behavior in free‐living Japanese pipistrelle bats (Pipistrellus abramus) can be disturbed by airport noise. We used audio recording to monitor foraging activities of bats at 11 sites around the runway of a municipal airport. We quantified noise level and spectra, aircraft activity, habitat type, nightly temperature, wind speed, and moon phase for each site. The analysis revealed that noise level and aircraft activity were significant negative predictors for the number of bat passes and feeding buzzes around the runway, even after controlling for the effects of other environmental factors. There was no marked spectral overlap between bat echolocation pulses and airport noise in the presence and absence of low‐flying aircraft. The spectro‐temporal parameters of echolocation vocalizations emitted by bats were dependent on noise level, aircraft activity, and habitat type. These results provide correlative evidence that airport noise can reduce foraging activities of wild pipistrelle bats. Our findings add to the current knowledge of adverse impacts of airport noise on foraging bats in artificial ecosystems and provide a basis for further research on the mechanisms behind noise pollution near airports.     

When to approach novel prey cues? Social learning strategies in frog-eating bats

Animals can use different sources of information when making decisions. Foraging animals often have access to both self-acquired and socially acquired information about prey. The fringe-lipped bat, Trachops cirrhosus, hunts frogs by approaching the calls that frogs produce to attract mates. We examined how the reliability of self-acquired prey cues affects social learning of novel prey cues. We trained bats to associate an artificial acoustic cue (mobile phone ringtone) with food rewards. Bats were assigned to treatments in which the trained cue was either an unreliable indicator of reward (rewarded 50% of the presentations) or a reliable indicator (rewarded 100% of the presentations), and they were exposed to a conspecific tutor foraging on a reliable (rewarded 100%) novel cue or to the novel cue with no tutor. Bats whose trained cue was unreliable and who had a tutor were significantly more likely to preferentially approach the novel cue when compared with bats whose trained cue was reliable, and to bats that had no tutor. Reliability of self-acquired prey cues therefore affects social learning of novel prey cues by frog-eating bats. Examining when animals use social information to learn about novel prey is key to understanding the social transmission of foraging innovations.     

THIRD REPORT OF THE S.A.O.S. LIST COMMITTEE

Tye, A. 1988. Foraging behaviour and selection of prey and perches by the Buffstreaked Chat Oenanthe bifasciata. Ostrich 59: 105–115.

Non-breeding Buffstreaked Chats Oenanthe bifasciata were studied in the Natal Drakensberg. Birds spent over 70% of their time foraging and 20% resting; both sexes sang, males c. 16% of the time. Individuals occupied overlapping home ranges; intra- and inter-specific aggressive interactions were recorded. Most foraging was by ground and aerial sallying from boulders, and all foraging methods were essentially sit-and-wait techniques. Buffstreaked Chats' most preferred perches were rocks 1,5-3 m high. Perches 1,5-3 m high were more likely to yield an aerial sally, while perches < 1,5 m were more likely to yield a ground sally or to be abandoned without a foraging attempt. Giving-up times were longer on perches 1,5-3 m high, but pre-capture waiting times were similar for perches of all heights. Giving-up times were longer than pre-capture times on perches 1,5-3 m high, but of similar duration to pre-capture times on lower perches. The major prey was grasshoppers, though ants, beetles, spiders and other insects were also eaten. When termites were swarming, birds switched to hunting them almost exclusively, thereby increasing their biomass intake rate. When termites were not available, at least 31% of the diet comprised prey 2 6 mm long. Aspects of the Buffstreaked Chat's biology are compared with other members of the genus Oenanthe.     

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

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

Perch selection in Sympetrum species (Odonata: Libellulidae): importance of vegetation structure and composition

1. Perching dragonflies are closely associated with the physical structure of vegetation because adults utilise plants when foraging, thermoregulating, and mate-seeking. However, little attention has been given to which structural attribute of vegetation is playing a key role within foraging habitat use. 2. This study focused on the influence of different features of perches on their selection by adult dragonflies. As a model group, a typical percher behavioural guild of Sympetrum was used and experimental plots with artificial perches and different structural properties were established. 3. It was found that adults preferred perch sticks with a wider diameter and larger spacing. It is assumed that these perching sites are advantageous because their base is more stable, they provide the best view for successful foraging, and there is no interference among individuals. 4. This study also revealed significant differences between male and female preferences. Females used less structured vegetation formed by thin perches in high densities. It is suggested that female discrimination is influenced by the higher competitiveness of males, which is related to their agonistic behaviour. 5. These results suggest that the availability of perches in the foraging habitat might be an essential requirement for adults. However, within the terrestrial surroundings of breeding sites, the structure of vegetation providing conditions for perching may be associated only with certain habitats. In intensive landscapes, physically structured vegetation can be limited or completely absent.     

Flying bats use serial sampling to locate odour sources

Olfactory tracking generally sacrifices speed for sensitivity, but some fast-moving animals appear surprisingly efficient at foraging by smell. Here, we analysed the olfactory tracking strategies of flying bats foraging for fruit. Fruit- and nectar-feeding bats use odour cues to find food despite the sensory challenges derived from fast flight speeds and echolocation. We trained Jamaican fruit-eating bats (Artibeus jamaicensis) to locate an odour reward and reconstructed their flight paths in three-dimensional space. Results confirmed that bats relied upon olfactory cues to locate a reward. Flight paths revealed a combination of odour- and memory-guided search strategies. During ‘inspection flights’, bats significantly reduced flight speeds and flew within approximately 6 cm of possible targets to evaluate the presence or absence of the odour cue. This behaviour combined with echolocation explains how bats maximize foraging efficiency while compensating for trade-offs associated with olfactory detection and locomotion.     

Behavioural elements reflect phenotypic colour divergence in a poison frog

The coexistence of both aposematic and cryptic morphs as different anti-predator strategies within a species seems to be an unusual phenomenon in nature. The strawberry poison frog, Oophaga pumilio, shows an astonishing colour diversity among populations in western Panama. In this study we selected a red and a green colour morph from two Panamanian islands (Isla Solarte and Isla Colón) for behavioural observations and measurements of conspicuousness. We found that red frogs were more visible to both conspecific frogs and potential predators than green frogs. Interestingly the difference in conspicuousness was most pronounced at the substrate that males used as principal calling places. Red males were more active and spent more time foraging than green males, which spent more time hidden. The association between conspicuousness of colouration and behaviour results in a more aposematic and a more cryptic anti-predator strategy. This is the first study which links differences in conspicuousness between animals on their natural backgrounds to differences in foraging as well as anti-predator behaviour and discusses the results in light of previous findings of toxicity analyses and potential costs and benefits of aposematism. To this end, our study adds a novel perspective for explaining extreme colour diversity between populations within an initially aposematic species.     

Patterns of reproduction and habitat use in an assemblage of Neotropical hylid frogs

We censused pond-breeding hylid frogs in northeastern Costa Rica weekly for 15 months to deseribe patterns of reproduction, habitat use, and to establish baseline data on relative abundance for members of the assemblage. Reproduction in the Costa Rican assemblage was seasonal and occurred only during wet months. Some species called, but none reproduced, during the dry season. Three species (Agalychnis callidryas, Hyla ebraccata, and Scinax elaeochroa) accounted for more than 75% of the observations made during the study. The species overlapped broadly in time and space, but differed in substrate use and phenology. Two species of leaf-breeding frogs (A. callidryas and A. saltator) used perches that were significantly higher than those used by the other species. Some phenological differences were associated with different mating strategies. Explosive breeders (Scinax elaeochroa and Smilisca baudinii) were most common early in the wet seasons. Prolonged breeders (A. callidryas and H. ebraccata) were the most persistent members of this assemblage. Predation affects early and late life history stages of these hylids. Predation on arboreal egg masses by two snake species was observed. Ctenid spiders preyed on recently metamorphosed frogs and small adults. Our weekly samples were pooled into 21-day periods so that we could compare our results with those obtained for two communities of breeding anurans from South America. The patterns observed in the Costa Rican assemblage differed from those reported for South American pond-breeding frogs, but in all three assemblages reproduction was associated with wet periods.     

Experimental evidence for group hunting via eavesdropping in echolocating bats

Group foraging has been suggested as an important factor for the evolution of sociality. However, visual cues are predominantly used to gain information about group members'' foraging success in diurnally foraging animals such as birds, where group foraging has been studied most intensively. By contrast, nocturnal animals, such as bats, would have to rely on other cues or signals to coordinate foraging. We investigated the role of echolocation calls as inadvertently produced cues for social foraging in the insectivorous bat Noctilio albiventris. Females of this species live in small groups, forage over water bodies for swarming insects and have an extremely short daily activity period. We predicted and confirmed that (i) free-ranging bats are attracted by playbacks of echolocation calls produced during prey capture, and that (ii) bats of the same social unit forage together to benefit from passive information transfer via the change in group members'' echolocation calls upon finding prey. Network analysis of high-resolution automated radio telemetry confirmed that group members flew within the predicted maximum hearing distance 94±6 per cent of the time. Thus, echolocation calls also serve as intraspecific communication cues. Sociality appears to allow for more effective group foraging strategies via eavesdropping on acoustical cues of group members in nocturnal mammals.     

Foraging activity of Rhinolophus hipposideros on the Island of Herrenchiemsee, Upper Bavaria

We studied the foraging behaviour of Rhinolophus hipposideros on the island “Herrenchiemsee” in Lake Chiemsee (Upper Bavaria) during summer 2001. The island offers extensively managed woodlands, highly structured open landscapes and a broad reed belt around the shore. On average the flight activity of the 6 radio tracked females outside the roost lasted 229 min per night. The home range size varied between 6.8 and 62.7 ha (mean 25.2 ha). The size of the activity centres varied between 2.8 and 8.2 ha (mean 5.3) and all except one were located almost exclusively in woodland. Within woodlands the bats did not select for specific spatial structures (different age classes of the stands or canopy densities). Only two bats regularly foraged in additional habitats outside woodlands. One of these bats used orchards and tree rows; the other foraged over artificial ponds and gardens adjoining to its woodland foraging area. We never found the bats foraging over the lake or the reed belt. Longer linear landscape elements as tree lines were used during commuting flights but there was no indication of a continuous foraging activity along these elements. Two females left the island to forage on the mainland in August after the fledging of juveniles. To reach the mainland shore, the bats had to fly at least 1.2 km across the lake.

Assuming that most foraging flights on the island occur in woodlands, a bat density in this habitat type of 0.7 bats/ha can be calculated.     

Vertebrate predation by sympatric tamarins, Saguinus mystax and Saguinus fuscicollis

Vertebrate predation was examined in sympatric moustached tamarins (Saguinus mystax) and saddle-back tamarins (Saguinus fuscicollis) in the Amazon rainforest of northeastern Peru. Both species prey on frogs and lizards, and very rarely on nestling birds. As a result of divergent foraging strategies, S. mystax primarily exploited frogs at higher strata of the forest, while S. fuscicollis predominantly preyed on reptiles in the lower strata and on the ground. This difference may strengthen the niche differentiation between these two tamarin species that exists with regard to other prey.     

Linking frugivore behavior to plant population dynamics

Despite the acknowledged importance of frugivores as seed dispersal agents we still lack a general understanding of the mechanisms by which these animals could shape plant populations and communities. We used a spatially explicit stochastic simulation to explore how frugivore movement decisions interact with landscape properties, thus affecting plant population dynamics through dispersal. The model simulated bird movement, foraging, seed deposition and plant recruitment. We assumed that plants lived only for one season and that recruitment was a function of local seed density. We also considered the effect of perches as non‐food landscape features. Our simulation experiments consisted in varying the parameters governing bird foraging decisions in relation to 1) how fruit abundance biased their movement, and 2) how the willingness to visit a plant or perch decreased with distance to current location. Simulated plant population dynamics was strongly influenced by bird behavior. The scale of foraging decisions had a much stronger effect on plant dynamics than biases due to fruit abundance. Birds tended to concentrate their activities in the center of the landscape where plants became more abundant, increasing local competition. The presence of perches reduced this tendency resulting in larger population sizes. The importance of perches highlights the fact that behaviors other than foraging can have a strong impact on the patterns of seed deposition and hence on plant population dynamics. Several recent studies have combined animal movement data with seed retention time in order to predict seed dispersal kernels. These studies usually emphasize the ecological implications of the scale and shape of such kernels. However, our simulation results reveal that movement directionality and the fact that birds moved mostly among plants and perches can have a major impact on plant population dynamics.