Research article: Sonar jamming in the field: Effectiveness and behavior of a unique prey defense

Wake Forest University, Department of Biology, Winston-Salem, NC 27106, USA.
Journal of Experimental Biology (Impact Factor: 2.9). 12/2012; 215(Pt 24):4278-87. DOI: 10.1242/jeb.076943
Source: PubMed


Bats and insects provide a model system for integrating our understanding of predator-prey ecology, animal behavior and neurophysiology. Previous field studies of bat-insect interactions have been limited by the technological challenges involved with studying nocturnal, volant animals that use ultrasound and engage in battles that frequently last a fraction of a second. We overcame these challenges using a robust field methodology that included multiple infrared cameras calibrated for three-dimensional reconstruction of bat and moth flight trajectories and four ultrasonic microphones that provided a spatial component to audio recordings. Our objectives were to document bat-moth interactions in a natural setting and to test the effectiveness of a unique prey defense - sonar jamming. We tested the effect of sonar jamming by comparing the results of interactions between bats and Grote's tiger moth, Bertholdia trigona, with their sound-producing organs either intact or ablated. Jamming was highly effective, with bats capturing more than 10 times as many silenced moths as clicking moths. Moths frequently combined their acoustic defense with two separate evasive maneuvers: flying away from the bat and diving. Diving decreased bat capture success for both clicking and silenced moths, while flying away did not. The diving showed a strong directional component, a first for insect defensive maneuvers. We discuss the timing of B. trigona defensive maneuvers - which differs from that of other moths - in the context of moth auditory neuroethology. Studying bat-insect interactions in their natural environment provides valuable information that complements work conducted in more controlled settings.

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Available from: Aaron Corcoran, Jan 22, 2014
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    • "Energetic cost typically scales with sound production rate (Prestwich 1994). Therefore, our results suggest that clicking in tiger moths has little energetic consequence, whether used for sonar jamming, acoustic aposematism, acoustic mimicry, or courtship (Conner 1999; Conner and Corcoran 2012). Clicking for sonar jamming may have evolved from clicking for acoustic aposematism, which requires only a simple sound-producing organ (Hristov and Conner 2005). "
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    ABSTRACT: Energetic cost can constrain how frequently animals exhibit behaviors. The energetic cost of acoustic signaling for communication has been the subject of numerous studies; however, the cost of acoustic signaling for predator defense has not been addressed. We studied the energetic cost and efficiency of sound production for the clicks produced by the moth Bertholdia trigona (Grote, 1879) (Grote’s bertholdia) to jam the sonar of predatory bats. This moth is an excellent model species because of its extraordinary ability to produce sound—it clicks at the highest known rate of any moth, up to 4500 clicks·s–1.Wemeasured the metabolic cost of clicking, resting, and flying from moths suspended in a respirometry chamber. Clicking was provoked by playing back an echolocation attack sequence. The cost of sound production for B. trigona was low (66% of resting metabolic rate) and the acoustic efficiency, or the percentage of metabolic power that is converted into sound, was moderately high (0.30% ± 0.15%) compared with other species. We discuss mechanisms that allow B. trigona to achieve their extraordinary clicking rates and high acoustic efficiency. Clicking for jamming bat sonar incurs negligible energetic cost to moths despite being the most effective known anti-bat defense. These results have implications for both the ecology of predator–prey interactions and the evolution of jamming signals. © 2015, National Research Council of Canada.All rights reserved.
    Full-text · Article · Feb 2015 · Canadian Journal of Zoology
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    • "Palatability for a moth species was taken as the averaged percentage of the moths consumed by bats. This method provides results that are similar to releasing silenced moths and observing whether free-flying, wild bats consume or drop moths after capture (Corcoran and Conner 2012; n. Dowdy, personal communication). "
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    ABSTRACT: Bats and their insect prey rely on acoustic sensing in predator prey encounters-echolocation in bats, tympanic hearing in moths. Some insects also emit sounds for bat defense. Here, we describe a previously unknown sound-producing organ in Geometrid moths-a prothoracic tymbal in the orange beggar moth (Eubaphe unicolor) that generates bursts of ultrasonic clicks in response to tactile stimulation and playback of a bat echolocation attack sequence. Using scanning electron microscopy and high-speed videography, we demonstrate that E. unicolor and phylogenetically distant tiger moths have evolved serially homologous thoracic tymbal organs with fundamentally similar functional morphology, a striking example of convergent evolution. We compared E. unicolor clicks to that of five sympatric tiger moths and found that 9 of 13 E. unicolor clicking parameters were within the range of sympatric tiger moths. Remaining differences may result from the small size of the E. unicolor tymbal. Four of the five sympatric clicking tiger moth species were unpalatable to bats (0-20 % eaten), whereas E. unicolor was palatable to bats (86 % eaten). Based on these results, we hypothesize that E. unicolor evolved tymbal organs that mimic the sounds produced by toxic tiger moths when attacked by echolocating bats.
    Full-text · Article · Jul 2014 · Journal of Comparative Physiology
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    • "Several moth species are known to easily detect lower call frequencies and subsequently avoid the bats [16] [47] [48]. Other Lepidoptera species can even jam the echolocation call which makes it very difficult for the bat to detect the prey [16] [49]. Call frequency was relative strongly related to Lepidoptera content, while cranial length and bodyweight did not show any relationship with the dietary content of Lepidoptera. "
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    ABSTRACT: The feeding habits of insectivorous bats are of great interest to people, because they are considered to be important in the control of insect pests. Here we present a study showing the relationship of bat morphology to differences in prey selection by various bat species. We compared dietary data from 10,884 faecal pellets, bodyweight, cranial length, forearm length and echolocation calls from published peer-reviewed studies for 92 bat species. We demonstrated that insectivorous bats tend to prefer certain insect orders which we have grouped as soft bodied insects, hard bodied insects and Lepidoptera. Wing characteristics which we measured by bodyweight-forearm ratio showed the strongest relationship with hard insects followed by longest cranial length. The content of soft insects in bat diets was negatively related to bodyweight, forearm length and longest cranial length. Lepidoptera content was positively related to the echolocation frequency with the maximum intensity (FMAXE), bats with high FMAXE fed on more Lepidoptera than those with low frequencies. We propose that a combination of dietary analysis and morphological analysis is needed to make strong inference about prey preference rather than comparing the dietary analysis with the insect abundance at the location were the bat or faecal pellets were collected.
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