Hunting at the highway: traffic noise reduces foraging efficiency in acoustic predators

Noise pollution from human traffic networks and industrial activity impacts vast areas of our planet. While anthropogenic noise effects on animal communication are well documented, we have very limited understanding of noise impact on more complex ecosystem processes, such as predator-prey interactions, albeit urgently needed to devise mitigation measures. Here, we show that traffic noise decreases the foraging efficiency of an acoustic predator, the greater mouse-eared bat (Myotis myotis). These bats feed on large, ground-running arthropods that they find by listening to their faint rustling sounds. We measured the bats' foraging performance on a continuous scale of acoustically simulated highway distances in a behavioural experiment, designed to rule out confounding factors such as general noise avoidance. Successful foraging bouts decreased and search time drastically increased with proximity to the highway. At 7.5 m to the road, search time was increased by a factor of five. From this increase, we predict a 25-fold decrease in surveyed ground area and thus in foraging efficiency for a wild bat. As most of the bats' prey are predators themselves, the noise impact on the bats' foraging performance will have complex effects on the food web and ultimately on the ecosystem stability. Similar scenarios apply to other ecologically important and highly protected acoustic predators, e.g. owls. Our study provides the empirical basis for quantitative predictions of anthropogenic noise impacts on ecosystem processes. It highlights that an understanding of the effects of noise emissions and other forms of 'sensory pollution' are crucially important for the assessment of environmental impact of human activities.     

Vessel noise cuts down communication space for vocalizing fish and marine mammals

Anthropogenic noise across the world's oceans threatens the ability of vocalizing marine species to communicate. Some species vocalize at key life stages or whilst foraging, and disruption to the acoustic habitat at these times could lead to adverse consequences at the population level. To investigate the risk of these impacts, we investigated the effect of vessel noise on the communication space of the Bryde's whale Balaenoptera edeni, an endangered species which vocalizes at low frequencies, and bigeye Pempheris adspersa, a nocturnal fish species which uses contact calls to maintain group cohesion while foraging. By combining long‐term acoustic monitoring data with AIS vessel‐tracking data and acoustic propagation modelling, the impact of vessel noise on their communication space was determined. Routine vessel passages cut down communication space by up to 61.5% for bigeyes and 87.4% for Bryde's whales. This influence of vessel noise on communication space exceeded natural variability for between 3.9 and 18.9% of the monitoring period. Additionally, during the closest point of approach of a large commercial vessel, <10 km from the listening station, the communication space of both species was reduced by a maximum of 99% compared to the ambient soundscape. These results suggest that vessel noise reduces communication space beyond the evolutionary context of these species and may have chronic effects on these populations. To combat this risk, we propose the application or extension of ship speed restrictions in ecologically significant areas, since our results indicate a reduction in sound source levels for vessels transiting at lower speeds.     

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.     

The use of supplementary foods by Australian magpies Gymnorhina tibicen: Implications for wildlife feeding in suburban environments

Abstract The provision of foods to wild birds is an extremely common practice among householders throughout the Western world. Nonetheless, concerns over potential impacts of the practice are currently being raised, including the possibility that some species may become reliant on human‐provided food. We compared the foraging and breeding ecology of pairs of fed and unfed Australian magpies Gymnorhina tibicen living in suburban environments in Brisbane, Queensland, Australia. Detailed behavioural observations of both foraging and chick provisioning were made for males and females of both groups throughout the breeding season. Natural foods dominated the diets of both fed and unfed magpies, making up 76% and 92% of all items consumed respectively. During the morning, fed magpies obtained fewer food items during ground foraging than did unfed birds, apparently because they visited suburban feeding stations more often during the early part of the day. At other times, the amount of food items obtained during foraging was similar for both fed and unfed birds. Magpies utilizing suburban feeding stations started all breeding activities significantly earlier than unfed magpies, except during the fledgling phase. Both fed and unfed magpie parents provisioned their chicks predominantly with natural food. Magpies were not reliant or dependent on supplementary food provided by wildlife feeders at any time during the breeding season. Although many magpies did utilize suburban feeding stations extensively, they continued to forage for and provision their chicks with natural food.     

The influence of predation risk on the feeding motivation and foraging strategy of juvenile Atlantic salmon

Juvenile Atlantic salmon, Salmo salar, changed their foraging strategy markedly after a brief exposure to a model trout predator, in ways that reduced their conspicuousness and hence risk of being preyed upon. After seeing the predator, the salmon were less likely to orientate to passing food particles, and having orientated, were less likely to attack them. They also reduced the extent of their movements, by only attacking those food particles that came close to them, and by delaying attacks until the food had reached its closest point. They were slower to orientate to approaching food items, possibly because more visual attention was switched to scanning for predators and less to feeding. However, there was no change in the outcome of attacks, indicating that the reduced food intake was not caused by a reduction in appetite. The relative priority given to foraging and predator avoidance varied with time elapsed since the predator was last sighted; as a consequence, intake rates in the 20 min following the predator presentation averaged only 33% of the pre-predator level, but had increased to 57% 20 min later, and had recovered completely within 2 h.     

Top carnivores increase their kill rates on prey as a response to human-induced fear

The fear induced by predators on their prey is well known to cause behavioural adjustments by prey that can ripple through food webs. Little is known, however, about the analogous impacts of humans as perceived top predators on the foraging behaviour of carnivores. Here, we investigate the influence of human-induced fear on puma foraging behaviour using location and prey consumption data from 30 tagged individuals living along a gradient of human development. We observed strong behavioural responses by female pumas to human development, whereby their fidelity to kill sites and overall consumption time of prey declined with increasing housing density by 36 and 42%, respectively. Females responded to this decline in prey consumption time by increasing the number of deer they killed in high housing density areas by 36% over what they killed in areas with little residential development. The loss of food from declines in prey consumption time paired with increases in energetic costs associated with killing more prey may have consequences for puma populations, particularly with regard to reproductive success. In addition, greater carcass availability is likely to alter community dynamics by augmenting food resources for scavengers. In light of the extensive and growing impact of habitat modification, our study emphasizes that knowledge of the indirect effects of human activity on animal behaviour is a necessary component in understanding anthropogenic impacts on community dynamics and food web function.     

Tandem Recruitment and Foraging in the Ponerine Ant <Emphasis Type="Italic">Pachycondyla harpax</Emphasis> (Fabricius)

Tandem running is a common recruitment strategy in ant species with small colony sizes. During a tandem run, an informed leader guides a usually naïve nestmate to a food source or a nest site. Some species perform tandem runs only during house hunting, suggesting that tandem running does not always improve foraging success in species known to use tandem running as a recruitment strategy, but more natural history information on tandem running under natural conditions is needed to better understand the adaptive significance of tandem recruitment in foraging. Studying wild colonies in Brazil, we for the first time describe tandem running in the ponerine ant Pachycondyla harpax (Fabricius). We asked if foragers perform tandem runs to carbohydrate- (honey) and protein-rich (cheese) food items. Furthermore, we tested whether the speed and success rate of tandem runs depend on the foraging distance. Foragers performed tandem runs to both carbohydrate food sources and protein-rich food items that exceed a certain size. The probability to perform a tandem run and the travelling speed increase with increasing foraging distances, which could help colonies monopolize more distant food sources in a competitive environment. Guiding a recruit to a food source is costly for leaders as ants are ~66% faster when travelling alone. If tandem runs break up (~23% of all tandem runs), followers do not usually discover the food source on their own but return to the nest. Our results show that tandem running to food sources is common in P. harpax, but that foragers modify their behaviour according to the type of food and its distance from the nest. Competition with other ants was intense and we discuss how tandem running in P. harpax might help colonies to build-up a critical number of ants at large food items that can then defend the food source against competitors.     

Anthropogenic noise compromises antipredator behaviour in European eels

Increases in noise‐generating human activities since the Industrial Revolution have changed the acoustic landscape of many terrestrial and aquatic ecosystems. Anthropogenic noise is now recognized as a major pollutant of international concern, and recent studies have demonstrated impacts on, for instance, hearing thresholds, communication, movement and foraging in a range of species. However, consequences for survival and reproductive success are difficult to ascertain. Using a series of laboratory‐based experiments and an open‐water test with the same methodology, we show that acoustic disturbance can compromise antipredator behaviour – which directly affects survival likelihood – and explore potential underlying mechanisms. Juvenile European eels (Anguilla anguilla) exposed to additional noise (playback of recordings of ships passing through harbours), rather than control conditions (playback of recordings from the same harbours without ships), performed less well in two simulated predation paradigms. Eels were 50% less likely and 25% slower to startle to an ‘ambush predator’ and were caught more than twice as quickly by a ‘pursuit predator’. Furthermore, eels experiencing additional noise had diminished spatial performance and elevated ventilation and metabolic rates (indicators of stress) compared with control individuals. Our results suggest that acoustic disturbance could have important physiological and behavioural impacts on animals, compromising life‐or‐death responses.     

A synthesis of two decades of research documenting the effects of noise on wildlife

Global increases in environmental noise levels – arising from expansion of human populations, transportation networks, and resource extraction – have catalysed a recent surge of research into the effects of noise on wildlife. Synthesising a coherent understanding of the biological consequences of noise from this literature is challenging. Taxonomic groups vary in auditory capabilities. A wide range of noise sources and exposure levels occur, and many kinds of biological responses have been observed, ranging from individual behaviours to changes in ecological communities. Also, noise is one of several environmental effects generated by human activities, so researchers must contend with potentially confounding explanations for biological responses. Nonetheless, it is clear that noise presents diverse threats to species and ecosystems and salient patterns are emerging to help inform future natural resource‐management decisions. We conducted a systematic and standardised review of the scientific literature published from 1990 to 2013 on the effects of anthropogenic noise on wildlife, including both terrestrial and aquatic studies. Research to date has concentrated predominantly on European and North American species that rely on vocal communication, with approximately two‐thirds of the data set focussing on songbirds and marine mammals. The majority of studies documented effects from noise, including altered vocal behaviour to mitigate masking, reduced abundance in noisy habitats, changes in vigilance and foraging behaviour, and impacts on individual fitness and the structure of ecological communities. This literature survey shows that terrestrial wildlife responses begin at noise levels of approximately 40 dBA, and 20% of papers documented impacts below 50 dBA. Our analysis highlights the utility of existing scientific information concerning the effects of anthropogenic noise on wildlife for predicting potential outcomes of noise exposure and implementing meaningful mitigation measures. Future research directions that would support more comprehensive predictions regarding the magnitude and severity of noise impacts include: broadening taxonomic and geographical scope, exploring interacting stressors, conducting larger‐scale studies, testing mitigation approaches, standardising reporting of acoustic metrics, and assessing the biological response to noise‐source removal or mitigation. The broad volume of existing information concerning the effects of anthropogenic noise on wildlife offers a valuable resource to assist scientists, industry, and natural‐resource managers in predicting potential outcomes of noise exposure.     

Ultraviolet vision and foraging in terrestrial vertebrates

Tetrachromatic colour vision, based on four ‘main’ colours and their combinations, is probably the original colour vision in terrestrial vertebrates. In addition to human visible waveband of light (400–700 nm) and three main colours, it also includes the near ultraviolet part of light spectrum (320–400 nm). The ecological importance of ultraviolet (UV) vision in animals has mainly been studied in the context of intra‐ and inter‐sexual signalling, but recently the importance of UV vision in foraging has received more attention. Foraging animals may use either UV cues (reflectance or absorbance) of food items or UV cues of the environment. So far, all diurnal birds studied (at least 35 species), some rodents (4 species), many reptilians (11 species) and amphibians (2 species) are likely able to see near UV light. This probably allows e.g. diurnal raptors as well as frugivorous, nectarivorous and insectivorous birds to use foraging cues invisible to humans. The possible role of UV cues and existing light conditions should be taken into account when food selection of vertebrate animals is studied, particularly, in experiments with artificial food items.     

Providing water for goats in arid landscapes: effects on feeding effort with regard to time period, herd size and secondary compounds

In arid regions, herbivores contend with a wide range of variables that influence their foraging ability. These may include plant secondary compounds (e.g. tannins and oxalates), water availability, time of day, and herd size. To determine the relative importance of these variables for goats living in a semi-desert, we measured the remaining food resources after foraging events (giving up densities-GUDs) as an index of foraging effort in artificial food patches. Time of day and the availability of drinking water had the greatest effect on GUDs. Goats achieved lower GUDs (i.e. ate more) in the afternoon than they did during the morning. We suggest this was due to missed opportunity costs of future foraging opportunities being lower in the afternoon. Ultimately, this implies that goats made short-term foraging decisions based on estimates of future feeding opportunities. When water was available, feeding effort increased and GUDs dropped almost 50%. For goats living in an arid environment, food and water are strong complementary resources. The presence of low to moderate levels of tannic or oxalic acid in food was a slight deterrent, raising the GUDs similarly. Larger herds ate more and thus obtained lower GUDs. In addition, there was an interaction of herd size and water, suggesting that in arid environments, the effect of water intensifies with population density. Our approach allowed us to quantify and rank the effects that disparate environmental factors had on the goats' foraging costs: water>time of day>herd size>plant secondary compounds. These findings ultimately demonstrate how the provision of water may increase grazing impacts by herbivores in arid landscapes.     

Vessel noise affects beaked whale behavior: results of a dedicated acoustic response study

Some beaked whale species are susceptible to the detrimental effects of anthropogenic noise. Most studies have concentrated on the effects of military sonar, but other forms of acoustic disturbance (e.g. shipping noise) may disrupt behavior. An experiment involving the exposure of target whale groups to intense vessel-generated noise tested how these exposures influenced the foraging behavior of Blainville's beaked whales (Mesoplodon densirostris) in the Tongue of the Ocean (Bahamas). A military array of bottom-mounted hydrophones was used to measure the response based upon changes in the spatial and temporal pattern of vocalizations. The archived acoustic data were used to compute metrics of the echolocation-based foraging behavior for 16 targeted groups, 10 groups further away on the range, and 26 non-exposed groups. The duration of foraging bouts was not significantly affected by the exposure. Changes in the hydrophone over which the group was most frequently detected occurred as the animals moved around within a foraging bout, and their number was significantly less the closer the whales were to the sound source. Non-exposed groups also had significantly more changes in the primary hydrophone than exposed groups irrespective of distance. Our results suggested that broadband ship noise caused a significant change in beaked whale behavior up to at least 5.2 kilometers away from the vessel. The observed change could potentially correspond to a restriction in the movement of groups, a period of more directional travel, a reduction in the number of individuals clicking within the group, or a response to changes in prey movement.     

Acoustic monitoring reveals the times and tides of harbor porpoise (Phocoena phocoena) distribution off central Oregon,U.S.A.

Harbor porpoises (Phocoena phocoena) are commonly observed in Oregon's nearshore marine environment yet knowledge of their ecosystem use and behavior remains limited, generating concerns for potential impacts on this species from future coastal development. Passive acoustic monitoring was used to investigate spatial and temporal variations in the presence and foraging activity of harbor porpoises off the Oregon coast from May through October 2014. Digital monitoring devices (DMONs) were deployed to record acoustic data (320 kHz sample rate) in two neighboring but bathymetrically different locations off the Oregon coast: (1) a site on the 30 m isobath in close proximity (<50 m) to a rocky reef, and (2) a site on the 60 m isobath in an open sandy environment. Data were analyzed with respect to two dynamic cyclic variables: diel and tidal phase. Porpoise presence at the rocky reef site was aligned with the ebb phase of the tidal forcing, while, harbor porpoise presence and foraging at the offshore, sandy bottom site was associated with night‐time foraging. The spatial and temporal patterns identified in this study suggest harbor porpoise habitat use is modulated by specific environmental conditions particular to each site that maximize foraging efficiency.     

Fine-scale food hoarding decisions in New Zealand Robins ( Petroica australis ): is inter-sexual competition important?

Competition for cache retrieval is hypothesised to influence food hoarding intensity. Previous work has tested this hypothesis by evaluating food hoarding rates during foraging bouts when animals are exposed to different levels of competition for cache retrieval. Little is known about how competition might influence fine-scale food hoarding decisions within foraging bouts. I evaluated fine-scale food hoarding decisions of New Zealand Robins (Petroica australis) by offering mealworms to competitively dominant males and subordinate females, both when they were alone and when they foraged together. I then compared food hoarding rates of sequentially handled prey between sexes and social conditions by assessing how the total number of prey cached increased with the total number of prey handled. Relationships for solitary females, solitary males and paired males were non-linear, indicating that they were more likely to consume initially handled prey, and increasingly likely to cache subsequently handled prey items. Non-linear rates of food hoarding may result from declines in the energetic value of prey that are consumed and stored internally as birds become satiated. Somewhat differently, the relationship for paired females was linear, indicating that paired females make a single food hoarding decision based on bout-level foraging conditions, which results in constant fine-scale food hoarding rates. Constant food hoarding rates in paired females, which experience the strongest competitive effects of any treatment, suggest that food consumption is consistently more advantageous than food hoarding under these conditions, regardless of satiation level. Overall results from this study indicate that New Zealand Robins continuously update food hoarding decisions according to their competitive environment and satiation levels, resulting in scale-dependent patterns in food hoarding intensity.     

Efficient or Inaccurate? Analytical and Numerical Modelling of Random Search Strategies

A large number of observational and theoretical studies have investigated animal movement strategies for finding randomly located food items. Many of these studies have claimed that a particular strategy is advantageous over other strategies or that the spatial distribution of the food items affects the search efficiency. Here, we study a deliberately idealised problem, in which a blind forager searches for re-visitable food items. We show analytically that the forager’s efficiency is completely independent of both its movement strategy and the spatial pattern of the food items and depends only on the density of food in the environment. However, in some cases, apparent optima in search strategies can arise as artefacts of inappropriate and inaccurate numerical simulations. We discuss modifications to the idealised foraging problem that can confer an advantage on certain strategies, including when the forager has some memory or knowledge of the environment; when the food items are non-revisitable; and when the problem is viewed in an evolutionary context.     

Adaptive foraging does not always lead to more complex food webs

Recent modeling studies exploring the effect of consumers’ adaptivity in diet composition on food web complexity invariably suggest that adaptivity in foraging decisions of consumers makes food webs more complex. That is, it allows for survival of a higher number of species when compared with non-adaptive food webs. Population-dynamical models in these studies share two features: parameters are chosen uniformly for all species, i.e. they are species-independent, and adaptive foraging is described by the search image model. In this article, we relax both these assumptions. Specifically, we allow parameters to vary among the species and consider the diet choice model as an alternative model of adaptive foraging. Our analysis leads to three important predictions. First, for species-independent parameter values for which the search image model demonstrates a significant effect of adaptive foraging on food web complexity, the diet choice model produces no such effect. Second, the effect of adaptive foraging through the search image model attenuates when parameter values cease to be species-independent. Finally, for the diet choice model we observe no (significant) effect of adaptive foraging on food web complexity. All these observations suggest that adaptive foraging does not always lead to more complex food webs. As a corollary, future studies of food web dynamics should pay careful attention to the choice of type of adaptive foraging model as well as of parameter values.     

Which senses play a role in nonhuman primate food selection? A comparison between squirrel monkeys and spider monkeys

In order to optimize foraging efficiency and avoid toxicosis, animals must be able to detect, discriminate, and learn about the predictive signals of potential food. Primates are typically regarded as animals that rely mainly on their highly developed visual systems, and little is known about the role that the other senses may play in food selection. It was therefore the aim of the present study to assess which senses are involved in the evaluation of food by two species of New World primates: the squirrel monkey and the spider monkey. To this end, six animals per species were repeatedly presented with both familiar and novel food items, and their behavior was videotaped and analyzed. To obtain a further indication of the relative importance of visual and chemosensory cues, the animals were also presented with familiar food items that were experimentally modified in color, odor, or both color and odor. The results demonstrate that squirrel monkeys and spider monkeys use olfactory, gustatory, and tactile cues in addition to visual information to evaluate novel food, whereas they mainly inspect familiar food items visually prior to consumption. Our findings also show that in both species the use of nonvisual cues decreased rapidly with repeated presentations of novel food, suggesting a fast multimodal learning process. Further, the two species clearly differ in their relative use of nonvisual cues when evaluating novel or modified food, with spider monkeys relying more on olfactory cues than squirrel monkeys, and squirrel monkeys relying more on tactile cues compared to spider monkeys.     

Climatic determinants of diet and foraging behaviour in baboons

Baboons (Papio spp.) are characterised by a large degree of variation in foraging behaviour and dietary composition. Previous analyses have suggested that much of this can be traced to differences in ecological conditions between sites. The proximate mechanism underlying these relationships is assumed to be mediated via the impact of climatic conditions on food availability, and ultimately the impact that this has on dietary composition. This paper examines these relationships more explicitly. Data from 15 baboon populations were used to assess the relationship between foraging variables and dietary composition. Only feeding time showed significant relationships with dietary composition, with percentage of time spent feeding decreasing with proportion of fruit in the diet, and increasing with the proportion of subterranean items. No relationships were found between diet composition and moving time or day journey length, although significant relationships were found between these variables and group size. The proportions of feeding time spent feeding on fruit, subterranean items and leaves were functions of the ecological conditions experienced by that population, although no relationships were found for the percentage of feeding time devoted to flowers or animal material. The relationships between the proportion feeding time spent on fruits, leaves and subterranean items and ecological variables could be best explained through understanding the way in which bush and tree level vegetation respond to the climatic environment and the impact this has on fruit availability. In this respect, temperature and seasonality are the key climatic parameters. This provides good support for the idea that the proximate mechanism underlying the relationship between foraging time and ecological variables is mediated via the impact of the climatic environment on vegetation structure and food availability. Similar factors have been proposed to explain much of the geographic variation in species diversity, suggesting that these relationships have far wider relevance and may account for much of the observed geographical variation in mammalian behaviour.     

Feeding strategy of the Tana mangabey (Cercocebus galeritus galeritus) (Mammalia: Primates)

Systematic data on the feeding behaviour and ecology of the Tana mangabey ( Cercocebus g. galeritus ) were collected over a period of 13 months in a riverine forest study site on the Tana River in Kenya. A total of 1151 hours of observation was conducted on two study groups, containing 36 and 17 animals respectively. Both spatial and temporal aspects of vegetation were studied. Particular emphasis was placed on quantification of foraging behaviour , which has not been treated as a distinct category in previous primate studies. (Feeding behaviour = foraging + eating.)
Dietary composition varied according to season, but there was also evidence that the diversity of the diet increased as food availability decreased. In addition, foraging increased when food was scarce, as did total distance moved and area searched for food. Results of analysis of major food items indicated that the mangabeys were possibly selecting such items in association with their metabolisable energy values. The conspicuous foraging behaviour and locomotor versatility of the mangabeys, combined with these quantitative observations, support the interpretation that this primate is a "generalist" in terms of feeding strategy, compared with "specialist" folivores exhibiting minimal searching and manipulation of food items. It is suggested that as "generalists" the mangabeys are particularly suited to forests lining meandering river systems, with their fluctuating mosaic of vegetation and food availability.     

How anthropogenic noise affects foraging

The influence of human activity on the biosphere is increasing. While direct damage (e.g. habitat destruction) is relatively well understood, many activities affect wildlife in less apparent ways. Here, we investigate how anthropogenic noise impairs foraging, which has direct consequences for animal survival and reproductive success. Noise can disturb foraging via several mechanisms that may operate simultaneously, and thus, their effects could not be disentangled hitherto. We developed a diagnostic framework that can be applied to identify the potential mechanisms of disturbance in any species capable of detecting the noise. We tested this framework using Daubenton's bats, which find prey by echolocation. We found that traffic noise reduced foraging efficiency in most bats. Unexpectedly, this effect was present even if the playback noise did not overlap in frequency with the prey echoes. Neither overlapping noise nor nonoverlapping noise influenced the search effort required for a successful prey capture. Hence, noise did not mask prey echoes or reduce the attention of bats. Instead, noise acted as an aversive stimulus that caused avoidance response, thereby reducing foraging efficiency. We conclude that conservation policies may seriously underestimate numbers of species affected and the multilevel effects on animal fitness, if the mechanisms of disturbance are not considered.