Bat Predation Research Articles

Determining Circadian Response of Adult MaleAcrobasis nuxvorella(Lepidoptera: Pyralidae) to Synthetic Sex Attractant Pheromone Through Time-Segregated Trapping With a New Clockwork Timing Trap

Mate finding is a key lifecycle event for the pecan nut casebearer, Acrobasis nuxvorella Neunzig, as it is for virtually all Lepidoptera, many of which rely on long-range, species-specific sex pheromones, regulated largely by circadian clocks. Adult male moths were trapped at discrete time intervals during the first two seasonal flights for 6 yr to determine times of peak activity associated with male response to pheromones. From 1997 to 2002, the Harris-Coble automated clockwork timing trap was used for hourly time-segregated sampling. Analysis of variance with linear contrasts determined that circadian response of A. nuxvorella males to pecan nut casebearer pheromone began at approximately 2100 hours, the first hour of total darkness, lasting for 6-7 h. It peaked from midnight to 0400 hours and ended at the onset of morning twilight, approximately 0500 hours. The hours of peak activity are hours of minimal bat predation. The study shows that pecan nut casebearer males become responsive to pheromone several hours before females start calling and remain responsive for at least 1 h after they stop. The extended response period conforms to studies of other polygamous Lepidoptera in which a selective advantage is conferred on early responding males in scramble competition for available females.

The cost of assuming the life history of a host: acoustic startle in the parasitoid fly Ormia ochracea

In the obligatory reproductive dependence of a parasite on its host, the parasite must trade the benefit of 'outsourcing' functions like reproduction for the risk of assuming hazards associated with the host. In the present study, we report behavioral adaptations of a parasitic fly, Ormia ochracea, that resemble those of its cricket hosts. Ormia females home in on the male cricket's songs and deposit larvae, which burrow into the cricket, feed and emerge to pupate. Because male crickets call at night, gravid female Ormia in search of hosts are subject to bat predation, in much the same way as female crickets are when responding to male song. We show that Ormia has evolved the same evasive behavior as have crickets: an acoustic startle response to bat-like ultrasound that manifests clearly only during flight. Furthermore, like crickets, Ormia has a sharp response boundary between the frequencies of song and bat cries, resembling categorical perception first described in the context of human speech.

Acquired Resistance to Saliva Anticoagulants by Prey Previously Fed upon by Vampire Bats (Desmodus rotundus): Evidence for Immune Response

Abstract Ranchers have observed that residual hemorrhage decreases after livestock suffer repeated bites from common vampire bats (Desmodus rotundus). We hypothesized that repeated exposure to the anticoagulants in the bats' saliva generated an immune response. We compared clotting time of blood mixed with Desmodus saliva between individuals of several species of livestock that were regularly exposed to vampire bats (“bat-attacked”) and individuals living where bat predation was not observed (“bat-naive”). We also compared the bleeding times of domestic sheep following a single defensive bite from a bat, before and after subjecting the animals to a series of feeding bites by Desmodus. Clotting time was significantly shorter in bat-attacked than in bat-naive livestock. Bleeding time after a provoked defensive bat bite was significantly shorter after sheep were exposed to a series of feeding bites from Desmodus. Bat predation induced increased resistance by the prey against the anticoagulants, suggesting an...

Release from bats: genetic distance and sensoribehavioural regression in the Pacific field cricket, Teleogryllus oceanicus

The auditory thresholds of the AN2 interneuron and the behavioural thresholds of the anti-bat flight-steering responses that this cell evokes are less sensitive in female Pacific field crickets that live where bats have never existed (Moorea) compared with individuals subjected to intense levels of bat predation (Australia). In contrast, the sensitivity of the auditory interneuron, ON1 which participates in the processing of both social signals and bat calls, and the thresholds for flight orientation to a model of the calling song of male crickets show few differences between the two populations. Genetic analyses confirm that the two populations are significantly distinct, and we conclude that the absence of bats has caused partial regression in the nervous control of a defensive behaviour in this insect. This study represents the first examination of natural evolutionary regression in the neural basis of a behaviour along a selection gradient within a single species.

Experimental Assessment of the Impacts of Northern Long-Eared Bats on OvipositingCulex(Diptera: Culicidae) Mosquitoes

The importance of predation as a mortality factor in adult mosquitoes has received only limited attention in the scientific literature. Despite the lack of consensus among researchers as to whether bats are important predators of mosquitoes, there have been no attempts to directly document the effect of bats on mosquito populations or behavior. We conducted an enclosure experiment to test the hypothesis that bats reduce the local abundance of ovipositing female mosquitoes by examining whether the northern long-eared bat (Myotis septentrionalis Trouessart) had an effect on Culex spp. (Diptera: Culicidae) oviposition, using naturally occurring mosquitoes, either through direct predation or trait mediated effects on mosquito behavior. We found a significant, 32% reduction in egg-laying activity associated with bat predation. Artificial oviposition habitats directly outside bat enclosures experienced no reduction in oviposition; we attributed the observed reduction in egg-laying activity to direct predation on ovipositing females by bats and not changes in mosquito behavior. In addition, we noted a decrease in the number of larval mosquitoes in enclosures exposed to bat predation. These results suggest the impact of aerial predators on pathogen transmission may be large, and warrants further scientific investigation.

Ultrasonic hearing in moths

Many moths possess ultrasound-sensitive ears, directly resulted from bat predation. Moth ears display an abundant diversity due to their body location, accessory structures, and number of auditory sensory cells. Anatomically, the moth ears are the simplest hearing organs in insects and most are tympanal organ with a tympanum. Eared moths have an optimal frequency range between 20 kHz and 50 kHz, which coincides with the peak frequency used by most insectivorous bats. The primary function of the moth ear is to detect and avoid the hunting of bats. Eared moths show a series of defensive behaviors, when they are exposed to the cries emitted by insectivorous bats. The presence of these tympanal organs also set the stage for the later evolution of ultrasonic courtship signals in the eared moth families. Over the years, entomologists worldwide have performed large numbers of studies on hearing of moths and their interactions with bats. This paper presents an overview of moth hearing, focusing on morphology, neurophysiology, and behavioral ecology.

Opportunistic predation on bats by the tawny owl Strix aluco

Abstract The presence of bats in the diet of tawny owls inhabiting the entrance parts of a large bat hibernation site in central Poland was compared in two periods. In the years 1985–1988 the median total number of hibernating bats per survey (522) was nearly 3 times lower than in the years 2002–2008 (1455). Along this trend the share of bats in tawny owls' diet increased respectively from 21.9% of vertebrate prey items to 36.5%. In areas without large bat concentrations they usually comprise up to 1% of vertebrate prey. This finding could be an evidence of an opportunistic feature of bat predation by owls.

Non‐morph specific predation of peppered moths (Biston betularia) by bats

Abstract 1. Industrial melanism in the peppered moth, Biston betularia, is one of the foremost examples of natural selection in action.2. Differential bird predation was suggested as the main agent for the evolution of melanism in the peppered moth by Tutt in the 1890s, with empirical support being published by Kettlewell in the 1950s.3. Some recent critiques that have attempted to undermine Kettlewell’s work have lacked objectivity, and have been answered previously.4. One criticism that has not previously been addressed is that of the role of bat predation in the case.5. The difficulty of using non‐visual differential predation by bats to explain the increase and decrease in melanism in the peppered moth, correlated as it is to pollution levels, is outlined.6. Predation experiments, in which moths of the typica and carbonaria forms of the peppered moth were released and observed at night, were used to determine whether bats differentially predate these forms.7. Results of experiments at three sites showed no significant differences in the level of bat predation of the two forms of peppered moth.

Bats Limit Insects in a Neotropical Agroforestry System

Exclosure experiments have demonstrated the effects of bird predation on arthropods. In a Mexican coffee plantation, we excluded foliage-gleaning bird and bat predators from coffee plants. Effects of bats and birds were additive. In the dry season, birds reduced arthropods in coffee plants by 30%; birds and bats together reduced arthropods by 46%. In the wet season, bats reduced arthropods by 84%, whereas birds reduced them by only 58%. We conclude that previous "bird" exclosure experiments may have systematically underestimated the effects of bats.

Bats Limit Arthropods and Herbivory in a Tropical Forest

Previous exclosure studies measuring the top-down control of arthropod abundance and herbivory combined the effects of birds and bats. We experimentally partitioned bird predation from bat predation in a lowland tropical forest in Panama and measured the direct effects (arthropod abundance) and indirect effects (herbivory). The exclusion of birds and bats each directly increased arthropod abundance on plants: Bird-exclosed plants contained 65% more, and bat-exclosed plants 153% more, arthropods than controls. Birds and bats also indirectly increased herbivory: Bird-exclosed plants suffered 67% more, and bat-exclosed plants 209% more, herbivory than controls. We conclude that bats have dramatic ecological effects that were previously overlooked.

Beware of bats, beware of birds: the auditory responses of eared moths to bat and bird predation

The allotonic frequency hypothesis (AFH) proposes that the preponderance of moths in the diets of some bats (e.g., Rhinolophidae) is the result of these bats echolocating at allotonic frequencies, that is, outside of the typical hearing range of most moths (ca., 20–60 kHz). The broader hearing range of African moths (5–110 kHz) suggests that their ears may function at frequencies usually considered allotonic. We investigated 1) whether moth ears were functionally audible to the Cape horseshoe bat, Rhinolophus capensis (Rhinolophidae), which forages in dense vegetation and echolocates at 84 kHz, and 2) whether moth auditory sensitivity below 10 kHz allows them to detect the rustling noises made by bird predators as they pursued moths through vegetation. The calls of R. capensis were audible to moths albeit over shorter distances relative to syntonic bats. Shorter detection distances combined with the constrained spaces in the cluttered habitat in which rhinolophids forage give moths both less time and less space within which to react to an attacking bat. Thus, the AFH in combination with habitat offers a better explanation for the preponderance of moths in the diets of rhinolophids than either of them on their own. Moths also responded both neurologically and behaviorally to the rustling sounds made by birds (Cape Bulbul, Pycnonotus capensis) as they pursued moths. We suggest that the high sensitivity of moths to frequencies from 5 to 10 kHz allows them to avoid these avian attacks by using responses that have traditionally been considered solely anti-bat behavior. Key words: allotonic frequency hypothesis, audition, bats, birds, moths, predation. [Behav Ecol]

Listening in Pheromone Plumes: Disruption of Olfactory-Guided Mate Attraction in a Moth by a Bat-Like Ultrasound

Nocturnal moths often use sex pheromones to find mates and ultrasonic hearing to evade echolocating bat predators. Male moths, when confronted with both pheromones and sound, thus have to trade off reproduction and predator avoidance depending on the relative strengths of the perceived conflicting stimuli. The ultrasonic hearing of Plodia interpunctella was investigated. A threshold curve for evasive reaction to ultrasound of tethered moths was established, and the frequency of best hearing was found to be between 40 and 70 kHz. Flight tunnel experiments were performed where males orienting in a sex pheromone plume were stimulated with 50 kHz pulses of different intensities. Pheromone-stimulated males showed increased defensive response with increased intensity of the sound stimulus, and the acoustic cue had long-lasting effects on their pheromone-mediated flight, revealing a cost associated with vital evasive behaviours.

Arginine Vasotocin Promotes Calling Behavior and Call Changes in Male Túngara Frogs

In the túngara frog, Physalaemus pustulosus, males alter calling behavior with changes in their social environment, adding ‘chucks’ to their advertisement calls in response to the calls of conspecific males. Other studies demonstrate that adding chucks increases the attractiveness of calls to females but also increases the risk of bat predation. In the current study, subcutaneous injections of the neuropeptide hormone arginine vasotocin (AVT) significantly increased chuck production in male túngara frogs. The effects of AVT on chuck production did not depend on the presence of playback stimuli, suggesting that AVT increased either the males’ general motivation to produce chucks or their responsiveness to the calls of distant males. Injections of AVT also increased the probability that males would call and decreased the latency to call after injection, supporting the hypothesis that AVT influences motivation to call. Finally, AVT inhibited a drop in call rate after the termination of a playback stimulus and increased call rate at a lower dose of AVT. The effects of AVT on chucks and call rate appear to be independent of each other, as there was no correlation between change in chuck production and change in call rate in individual males. We conclude that AVT may play an important role in socially-mediated call changes that result from competition for mates. The behavioral changes induced by AVT might increase a male’s attractiveness to females, and also may be consistent with an aggressive response to another túngara frog male.

Snakes preying on bats: new records from Brazil and a review of recorded cases in the Neotropical Region

Predation on bats by snakes is relatively infrequently reported in the literature, though it may actually not be an uncommon phenomenon, since bat colonies represent a potential concentration of food for many medium-sized or large snakes. Herein we describe four events of bat predation by snakes and present a review of predation records of snakes on bats in the Neotropics compiled from the literature. A total of 20 species of snakes have been recorded so far as predators of bats in the New World tropics, with boiids being represented by the greatest number of cases. Due to the semi-arboreal habits of most of its species, their large size and their usual preference for mammalian prey, the Boiidae are probably the main reptilian predators of bats in the Neotropics, though predation by colubrids may also be relatively frequent. Two types of predatory events can be pointed out: (1) on active bats outside refuges or exiting them, and (2) on animals (active or inactive) inside refuges. The former strategy is apparently used mainly by boiids, whereas the latter strategy appears to be the one most used by large colubrids.

Behaviors of Western Spruce Budworm Moths (Choristoneura occidentalis) as Defences Against Bat Predation

We investigated potential defense behaviors of adult western spruce budworm (Choristoneura occidentalis), a non-auditive lepidopteran, against bat predation. Although western spruce budworm moths started to fly before sunset, earlier than many species of moths, temporal isolation of flying moths from foraging bats was incomplete as moths were most active after sunset once bats were foraging. Flying C. occidentalis were most active close to their host trees, and thus were isolated from some bat activity because vegetation limits foraging by some bats. Moths mostly flew near the tops of trees, an area that may have a high predation pressure from bats. Resting western spruce budworm spent little time fluttering their wings or crawling, behaviors that are used as cues by gleaning bats. The outbreak nature of this species, in which large numbers of moths are active at one time, may allow dilution effects to reduce predation risk.

Predation of a Bat by American Crows, <em>Corvus brachyrhynchos</em>

This report documents predation and possible group hunting of a bat by American Crows (Corvus brachyrhynchos). I observed a group of several crows appear to cooperate in order to ground and catch a bat. Predation of bats by birds in North America is relatively rare, and bat predation by crows has not been previously reported. A cooperative attack would be consistent with other group behaviours of the species, including territoriality, breeding and foraging.

Timing of praying mantis evasive responses during simulated bat attack sequences

Praying mantids perform evasive maneuvers that vary with the level of danger posed by their bat predators. The vocalization pattern of attacking bats provides cues that mantids can potentially use to decide how and when to respond. Using pulse trains simulating bat attack echolocation sequences, this study determines when in the attack sequence the mantis power dive (its response to high-level threat) occurs and predicts the parameters within the echolocation sequence that are important for eliciting the response. For sequences with a rapid transition from low to high pulse repetition rates (PRRs), the evasive response occurred close to the point during the simulated sequence when the bat would have contacted the mantis. However, the evasive response occurred earlier if the transition was gradual. Regardless of the transition type, the prediction data show that sequences trigger the response when PRRs reach 20-40 pulses s(-1). These results suggest that a bat gradually increasing its PRR could 'tip off' the mantis, enabling it to escape. Attack sequences contain gradual transitions when bats engage in strobing behavior, an echolocation phenomenon that may help the bat perceive the auditory scene. Conversely, bat attack sequences that contain rapid increases in PRR close to the point of capture could circumvent the mantid's auditory defense. Based on these findings, mantids as well as other insects could benefit from having a back-up defense response to offset any advantage the bat gains by rapidly switching from low to high PRRs.

Cohabitation and predation by insectivorous bats on eared moths in subterranean roosts

Most regions of the world support moth species that use caves as diurnal roosts and/or as overwintering and mating sites. Although subterranean roosts are often also occupied by insectivorous bats, nothing is known about moth–bat interaction at these sites. The frequency of cohabitation and the dynamics of moth–bat interaction at roosts were examined during surveys at 30 known bat roosts in eastern Australia; 15 disused mines and 15 natural caves. Moths and bats cohabited in 20 roosts (67%); however, only two species of eared moths, Speiredonia spectans and S. mutabilis (Noctuidae), were observed. These large (wingspan up to 75 mm) species show a classic escape response to ultrasound. Moths used roosts occupied by bats with both frequency modulated (FM) (four species) and constant frequency (CF) (two species) echolocation calls. Signal frequencies of these bats had ranges of 23–25 and 44–71 kHz. Moths were absent from roosts occupied by high-frequency (>140 kHz) CF bats. Predator–prey interaction was assessed by studying a sub-sample of six roosts occupied by S. spectans and the horseshoe bat Rhinolophus megaphyllus. Speiredonia spectans and R. megaphyllus cohabited roosts throughout the year. Bats captured and consumed moths in these roosts. The numbers of moth wings on the floor of roosts were counted to assess rates of predation. Bats consumed 209 moths at the six roosts over a 12-month period, representing 19% of the moth population at the start of the study. The study establishes that moth–bat cohabitation of roosts is relatively common in eastern Australia and that bats do capture moths in these sites. Bat predation seems to be a significant source of mortality of moths that occupy subterranean roosts.

Foraging and mate‐finding in the silver Y moth, Autographa gamma (Lepidoptera: Noctuidae) under the risk of predation

Animal foraging and reproductive behaviour is influenced by other simultaneous demands such as predator avoidance. The trade‐offs between these demands may depend on sex or mating experience. This study demonstrates that the olfactory‐mediated foraging and mate‐seeking behaviours in the silver Y moths, Autographa gamma, are affected by auditory cues mimicking their bat predators. Both males and females changed their foraging behaviour under simulated predation risk. Fewer moths reached the odour source following sound stimulation and the time to find the odour source increased by up to 250%. However, there were no significant differences between male and female ability to reach the plant odour source or the duration of the flight towards the source when stimulated with ultrasound. Hence females are not more cautious than males when observed in the same behavioural context. Risk‐taking in males was independent of whether they were flying toward a flower odour or sex pheromones having equal attractive value. This indicates that the trade‐off between olfactory and acoustic cues is independent the type of odour. Mated females were not as strongly affected by sound as non‐mated, indicating that flower odours have a higher adaptive value for mated females, suggesting that some processes following mating experience influence the trade‐off between flower odours and simulated bat sounds.

Bat predation on nocturnally migrating birds.

Bat predation on birds is a very rare phenomenon in nature. Most documented reports of bird-eating bats refer to tropical bats that occasionally capture resting birds. Millions of small birds concentrate and cross over the world's temperate regions during migration, mainly at night, but no nocturnal predators are known to benefit from this enormous food resource. An analysis of 14,000 fecal pellets of the greater noctule bat (Nyctalus lasiopterus) reveals that this species captures and eats large numbers of migrating passerines, making it the only bat species so far known that regularly preys on birds. The echolocation characteristics and wing morphology of this species strongly suggest that it captures birds in flight.