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The Atiu Swiftlet Aerodramus sawtelli is endemic to the Cook Island of Atiu and has an estimated total population of less than 400, rendering it one of the world’s most globally endangered bird species. Over a series of five visits to Atiu, we collected data on the distribution of foraging swiftlets on the island, and their foraging and echolocation behaviour. The bird favours forests, agriculturally developed areas such as croplands, and populated sections of the island (e.g. gardens) but avoids the dry, upraised coral ring (makatea) of Atiu. It appears able to readily exploit new insects after they have immigrated to Atiu and may act as a natural control agent on pest species (e.g. Xyleborus perforans and Atrichopogon jacobsoni). We reanalysed the swiftlets’ echolocation calls within one of their roost caves in conjunction with new recordings. The calls do not contain ultrasonic components and are uniquely single clicks compared to the echolocation vocalisations of other swiftlet species. The minimal impact of human disturbance on the remote nesting caves of this bird suggests that its numbers, although small, represent a stable population. [ABSTRACT FROM PUBLISHER]

Neotropical katydids (Orthoptera: Tettigoniidae) are preyed on by gleaning bats, which are known to use male calling songs to locate them. At least one katydid species has been reported to stop singing in response to bat echolocation calls. To investigate the relationship between this behavioural defence and ecological and sensory factors, we surveyed calling song characteristics, song cessation in response to the echolocation calls of a sympatric gleaning bat ( Trachops cirrhosus), and T-cell responses (an auditory interneuron sensitive to ultrasound) in five katydid species from Panamá. The two katydid species that stopped singing in response to bat calls ( Balboa tibialis and Ischnomela gracilis, Pseudophyllinae) also had the highest T-cell spike number and rate in response to these stimuli. The third pseudophylline species ( Docidocercus gigliotosi) did not reliably cease singing and had low T-cell spiking activity. Neoconocephalus affinis (Copiphorinae) produced continuous calling song, possibly preventing males from hearing the bat during singing, and did not show a behavioural response despite high T-cell activity in response to bat calls. Steirodon rufolineatum (Phaneropterinae) did not cease singing and differed in T-cell activity compared to the other species. T-cell function might not be conserved in katydids, and evidence for this idea is discussed. [ABSTRACT FROM AUTHOR]

Bats that glean prey (capture them from surfaces) produce relatively inconspicuous echolocation calls compared to aerially foraging bats and could therefore be difficult predators to detect, even for insects with ultrasound sensitive ears. In the cricket Teleogryllus oceanicus, an auditory interneuron (AN2) responsive to ultrasound is known to elicit turning behaviour, but only when the cricket is in flight. Turning would not save a cricket from a gleaning bat so we tested the hypothesis that AN2 elicits more appropriate antipredator behaviours when crickets are on the ground. The echolocation calls of Nyctophilus geoffroyi, a sympatric gleaning bat, were broadcast to singing male and walking female T. oceanicus. Males did not cease singing and females did not pause walking more than usual in response to the bat calls up to intensities of 82 dB peSPL. Extracellular recordings from the cervical connective revealed that the echolocation calls elicited AN2 action potentials at high firing rates, indicating that the crickets could hear these stimuli. AN2 appears to elicit antipredator behaviour only in flight, and we discuss possible reasons for this context-dependent function. [ABSTRACT FROM AUTHOR]

The article provides information on a study that illustrated that the activity of a single auditory neuron (the A1 cell) provides enough information for the toxic dogbane tiger moth, Cycnia tenera, to decide when to initiate defensive sound production in the face of bats. It examines the alternative hypothesis that auditory afferent A2 is not necessary for initiating defensive sound production in response to bat echolocation calls, using longer pulses of short and long rise times to effect differences in A1 and A2 activity over a range of maximum sound pressure levels.

We investigated whether the use of primary or secondary behavioural defences is related to prey sensory thresholds using two species of North American katydids, Neoconocephalus ensiger and Amblycorypha oblongifolia. Male katydids produce Intense calling songs to attract mates, and many gleaning bat species are known to use these calls to locate them as prey. Low duty cycle calling (i.e. sporadic calls) is a primary defence against gleaning bats (prevents attacks), and song cessation is a secondary defence (enables survival of an attack), for which these two species show behavioural differences. Echolocation calls of Myotis septentrionalis, a sympatric gleaning bat species, were broadcast to singing katydids and to neural preparations of these katydids to test if differences in behavioural response were related to differences in auditory sensitivity. We measured thresholds and firing patterns of the T-cell, an auditory interneuron involved in predator detection. We hypothesized that low duty cycle calling is the best defence for species not sensitive enough to mount a secondary defence in response to predator cues; therefore, we predicted that N. ensiger(high duty cycle song) would have lower behavioural and T-cell thresholds than A. oblongifolia (low duty cycle song). Although more N. ensiger ceased singing than A. oblongifolia, the number and maximum firing rate of T-cell action potentials did not differ between species for echolocation call sequences. We suggest that the T-cell has divergent functions within the Tettigoniidae, including predator and mate detection, and the function could be context dependent in some species. [ABSTRACT FROM AUTHOR]

Certain tiger moths (Arctiidae) defend themselves against bats by phonoresponding to their echolocation calls with trains of ultrasonic clicks. The dogbane tiger moth, Cycnia tenera, preferentially phonoresponds to the calls produced by attacking versus searching bats, suggesting that it either recognizes some acoustic feature of this phase of the bat's echolocation calls or that it simply reacts to their increased power as the bat closes. Here, we used a habituation/generalization paradigm to demonstrate that C. ten era responds neither to the shift in echolocation call frequencies nor to the change in pulse duration that is exhibited during the bat's attack phase unless these changes are accompanied by either an increase in duty cycle or a decrease in pulse period. To separate these features, we measured the moth's phonoresponse thresholds to pulsed stimuli with variable versus constant duty cycles and demonstrate that C. tenera is most sensitive to echolocation call periods expressed by an attacking bat. We suggest that, under natural conditions, C. tenera identifies an attacking bat by recognizing the pulse period of its echolocation calls but that this feature recognition is influenced by acoustic power and can be overridden by unnaturally intense sounds. [ABSTRACT FROM AUTHOR]

We studied the efficiency and effects of the multiple sensory cues of tiger moths on echolocating bats. We used the northern long-eared bat, Myotis septentrionalis, a purported moth specialist that takes surface-bound prey (gleaning) and airborne prey (aerial hawking), and the dogbane tiger moth, Cycnia tenera, an eared species unpalatable to bats that possesses conspicuous colouration and sound-producing organs (tymbals). This is the first study to investigate the interaction of tiger moths and wild-caught bats under conditions mimicking those found in nature and to demand the use of both aerial hawking and gleaning strategies by bats. Further, it is the first to report spectrograms of the sounds produced by tiger moths while under aerial attack by echolocating bats. During both aerial hawking and gleaning trials, all muted C. tenera and perched intact C. tenera were attacked by M. septentrionalis, indicating that M. septentrionalis did not discriminate C. tenera from palatable moths based on potential echoic and/or non-auditory cues. Intact C. tenera were attacked significantly less often than muted C. tenera during aerial hawking attacks: tymbal clicks were therefore an effective deterrent in an aerial hawking context. During gleaning attacks, intact and muted C. tenera were always attacked and suffered similar mortality rates, suggesting that while handling prey this bat uses primarily chemical signals. Our results also show that C. tenera temporally matches the onset of click production to the ‘approach phase’ echolocation calls produced by aerial hawking attacking bats and that clicks themselves influence the echolocation behaviour of attacking bats. In the context of past research, these findings support the hypotheses that the clicks of arctiid moths are both an active defence (through echolocation disruption) and a reliable indicator of chemical defence against aerial-hawking bats. We suggest these signals are specialized for an aerial context. [ABSTRACT FROM AUTHOR]

The literature suggests that in familiar laboratory settings, Indian false vampire bats (Megaderma lyra, family Megadermatidae) locate terrestrial prey with and without emitting echolocation calls in the dark and cease echolocating when simulated moonlit conditions presumably allow the use of vision. More recent laboratory-based research suggests thatM. lyrauses echolocation throughout attacks but at emission rates much lower than those of other gleaning bats. We present data from wild-caught bats hunting for and capturing prey in unfamiliar conditions mimicking natural situations. By varying light level and substrate complexity we demonstrated that huntingM. lyraalways emit echolocation calls and that emission patterns are the same regardless of light/substrate condition and similar to those of other wild-caught gleaning bats. Therefore, echoic information appears necessary for this species when hunting in unfamiliar situations, while, in the context of past research, echolocation may be supplanted by vision, spatial memory or both in familiar spaces. [ABSTRACT FROM AUTHOR]

1. Auditory sensitivities and ultrasound avoidance behaviour of two exclusively diurnal moths were examined to test the prediction that total isolation from the predatory effects of echolocating bats will result in the regression of these sensory systems and/or the defences they evoke. 2. The silent geometrid, Trichodezia albovittata, possessed large ears with auditory neural thresholds similar to or better than those of a sympatric, exclusively nocturnal geometrid moth. Trichodezia albovittata readily responded with evasive flight to ultrasound and it is suggested that if this moth has become completely isolated from bats its ears are functionally vestigial, at least in the population studied here. 3. In contrast, while the sound-producing arctiid, Lycomorpha pholus, had low auditory sensitivity based on neural thresholds, it still responded with flight changes to ultrasound. it did not, however, produce sounds when stimulated ultrasonically. It is suggested that the ears of this moth are functionally vestigial for bat-detection purposes but may be used for short-distance social communication. [ABSTRACT FROM AUTHOR]

The simple auditory system of noctuoid moths has long been a model for anti-predator studies in neuroethology, although these ears have rarely been experimentally stimulated by the sounds they would encounter from naturally attacking bats. We exposed the ears of five noctuoid moth species to the pre-recorded echolocation calls of an attacking bat (Eptesicus fuscus) to observe the acoustic encoding of the receptors at this critical time in their defensive behaviour. The B cell is a non-tympanal receptor common to all moths that has been suggested to respond to sound, but we found no evidence of this and suggest that its acoustic responsiveness is an artifact arising from its proprioceptive function. The A1 cell, the most sensitive tympanal receptor in noctuid and arctiid moths and the only auditory receptor in notodontid moths, encodes the attack calls with a bursting firing pattern to a point approximately 150 ms from when the bat would have captured the moth. At this point, the firing of the A1 cell reduces to a non-bursting pattern with longer inter-spike periods, suggesting that the moth may no longer express the erratic flight used to escape very close bats. This may be simply due to the absence of selection pressure on moths for auditory tracking of bat echolocation calls beyond this point. Alternatively, the reduced firing may be due to the acoustic characteristics of attack calls in the terminal phase and an acoustic maneuver used by the bat to facilitate its capture of the moth. Although the role of less sensitive A2 cell remains uncertain in the evasive flight responses of moths it may act as a trigger in eliciting sound production, a close-range anti-bat behaviour in the tiger moth, Cycnia tenera. [ABSTRACT FROM AUTHOR]

Presents information on a study which proposes that the sensitive auditory receptor cell (A1) in the two-celled ears of certain noctuoid stimulus intensities. Information on the kind of ears possessed by notodontid moths; Materials and methods used in the study; Discussion of the results.

Discusses how the spotted bat Euderma maculatum demonstrates echolocation calls that are lower in frequency, shorter in duration and fainter in intensity compared with Eptesicus fuscus. Evaluation of Eu maculatum's echolocation calls on moths; Echolocation call characteristics of the Euderma.

Determines the natural response of an arctiid to the approach of a hunting bat using a recording of the attack sequence of echolocation calls emitted by the big brown bat as a playback to the dogbane tiger moth. Animals; Playback procedures.