Ralph Simon

Floral acoustics: conspicuous echoes of a dish-shaped leaf attract bat pollinators

A bat-pollinated plant has dish-shaped leaves with conspicuous echoes that serve as acoustic attractors. The visual splendor of many diurnal flowers serves to attract visually guided pollinators such as bees and birds, but it remains to be seen whether bat-pollinated flowers have evolved analogous echo-acoustic signals to lure their echolocating pollinators. Here, we demonstrate how an unusual dish-shaped leaf displayed above the inflorescences of the vine Marcgravia evenia attracts bat pollinators. Specifically, this leaf’s echoes fulfilled requirements for an effective beacon, that is, they were strong, multidirectional, and had a recognizable invariant echo signature. In behavioral experiments, presence of the leaves halved foraging time for flower-visiting bats.

Size discrimination of hollow hemispheres by echolocation in a nectar feeding bat

SUMMARY Nectar feeding bats use echolocation to find their flowers in the dense growth of tropical rainforests, and such flowers have evolved acoustic features that make their echo more conspicuous to their pollinators. To shed light on the sensory and cognitive basis of echoacoustic object recognition we conducted a size discrimination experiment with the nectarivorous bat Glossophaga soricina and compared the bats behavioural performance with the echoic features of the training objects. We chose a simple geometric form, the hollow hemisphere, as the training object because of its resemblance to the bell-shaped concave form of many bat flowers, as well as its special acoustic qualities. The hemispheres showed a characteristic echo pattern, which was constant over a wide range of angles of sound incidence. We found systematic size-dependent changes in the echos temporal and spectral pattern as well as in amplitude. Bats were simultaneously confronted with seven different sizes of hollow hemispheres presented from their concave sides. Visits to one particular size were rewarded with sugar water, while we recorded the frequency of visits to the unrewarded hemispheres. We found that: (1) bats learned to discriminate between hemispheres of different size with ease; (2) the minimum size difference for discrimination was a constant percentage of the hemispheres size (Weber fraction: approximately 16% of the radius); (3) the comparison of behavioural data and impulse response measurements of the objects echoes yielded discrimination thresholds for mean intensity differences (1.3 dB), the temporal pattern (3-22 μs) and the change of spectral notch frequency (approximately 16%). We discuss the advantages of discrimination in the frequency and/or time domain.

Bats Are Acoustically Attracted to Mutualistic Carnivorous Plants

Mutualisms between plants and animals shape the worlds ecosystems. In such interactions, achieving contact with the partner species is imperative. Plants regularly advertise themselves with signals that specifically appeal to the partners perceptual preferences. For example, many plants have acquired traits such as brightly colored, fragrant flowers that attract pollinators with visual, olfactory, or--in the case of a few bat-pollinated flowers--even acoustic stimuli in the form of echo-reflecting structures. However, acoustic attraction in plants is rare compared to other advertisements and has never been found outside the pollination context and only in the Neotropics. We hypothesized that this phenomenon is more widespread and more diverse as plant-bat interactions also occur in the Paleotropics. In Borneo, mutualistic bats fertilize a carnivorous pitcher plant while roosting in its pitchers. The pitchers orifice features a prolonged concave structure, which we predicted to distinctively reflect the bats echolocation calls for a wide range of angles. This structure should facilitate the location and identification of pitchers even within highly cluttered surroundings. Pitchers lacking this structure should be less attractive for the bats. Ensonifications of the pitchers around their orifice revealed that this structure indeed acts as a multidirectional ultrasound reflector. In behavioral experiments where bats were confronted with differently modified pitchers, the reflectors presence clearly facilitated the finding and identification of pitchers. These results suggest that plants have convergently acquired reflectors in the Paleotropics and the Neotropics to acoustically attract bats, albeit for completely different ecological reasons.

Acoustic communication in plant–animal interactions

Acoustic communication is widespread and well-studied in animals but has been neglected in other organisms such as plants. However, there is growing evidence for acoustic communication in plant-animal interactions. While knowledge about active acoustic signalling in plants (i.e. active sound production) is still in its infancy, research on passive acoustic signalling (i.e. reflection of animal sounds) revealed that bat-dependent plants have adapted to the bats echolocation systems by providing acoustic reflectors to attract their animal partners. Understanding the proximate mechanisms and ultimate causes of acoustic communication will shed light on an underestimated dimension of information transfer between plants and animals.

Biosonar resolving power : echo-acoustic perception of surface structures in the submillimeter range

The minimum distance for which two points still can be separated from each other defines the resolving power of a visual system. In an echo-acoustic context, the resolving power is usually measured as the smallest perceivable distance of two reflecting surfaces on the range axis and is found to be around half a millimeter for bats employing frequency modulated (FM) echolocation calls. Only few studies measured such thresholds with physical objects, most often bats were trained on virtual echoes i.e., echoes generated and played back by a computer; moreover, bats were sitting while they received the stimuli. In these studies differences in structure depth between 200 and 340 μm were found. However, these low thresholds were never verified for free-flying bats and real physical objects. Here, we show behavioral evidence that the echo-acoustic resolving power for surface structures in fact can be as low as measured for computer generated echoes and even lower, sometimes below 100 μm. We found this exceptional fine discrimination ability only when one of the targets showed spectral interferences in the frequency range of the bats′ echolocation call while the other target did not. This result indicates that surface structure is likely to be perceived as a spectral quality rather than being perceived strictly in the time domain. Further, it points out that sonar resolving power directly depends on the highest frequency/shortest wavelength of the signal employed.

Mitigating Bat Mortality with Turbine-Specific Curtailment Algorithms: A Model Based Approach

Alarmingly high numbers of bats are being killed at wind turbines worldwide, raising concerns about the cumulative effects of bat mortality on bat populations. Mitigation measures to effectively reduce bat mortality at wind turbines while maximising energy production are of paramount importance. Operational mitigation (i.e. feathering wind turbine rotors at times of high collision risk for bats) is currently the only strategy that has been shown to substantially reduce bat mortality. This study presents a model based approach for developing curtailment algorithms that account for differences in bat activity over the year and night-time and are specific to the activity level at a certain wind turbine. The results show that easily measurable variables (wind speed, month, time of night) can predict times of higher bat activity with a high temporal resolution. A recently published collision model that was developed based on an excessive carcass search study is then applied to predict bat collision rate based on the modelled bat activity. Using the ratio of wind energy revenue and collision rate, 10 min intervals were weighted, so that turbines are stopped when collision rate is high and loss in revenue is low. A threshold of two dead bats per year and turbine resulted in a mean loss in annual revenue of 1.4%. The presented approach of acoustic monitoring at the nacelle and turbine specific curtailment has become the standard method to mitigate collision risk of bats at wind turbines in Germany.

Sensory challenges for trawling bats: Finding transient prey on water surfaces

Bats are able to identify obstacles and prey objects based exclusively on acoustic information acquired via echolocation. To assess the echo information potentially available to the trawling bat Noctilio leporinus, prey objects were ensonified with artificial bat calls and deduced echo target strengths (TS) of the reflected signals. The artificial calls consisted either of constant frequency (CF) or frequency modulated (FM) sounds. Detection distances were calculated for call intensities of N. leporinus emitted in the field and in confined space. Measurements of a transient target consisting of a brief water splash and subsequently expanding water ripples revealed that concentrically expanding water ripples can provide sufficiently loud echoes to be detected by trawling bats. Experiments with stationary targets revealed differences in TS depending on the type of signal used (CF or FM). A calculated maximum detection distance between 4.5 and 13.7u2009m for all measured targets indicates that prey detection in this very loud calling species occurs much earlier than suggested by estimations based on modifications in echolocation or flight behavior.

Analysis of tonpilz with flexing pistons.

The acoustic loading of each of the first six modes of a double piston piezoelectric stack‐driven underwater acoustic transducer is found using Botman’s method [NAA report NA65H‐1024, June 1965] revised with the use of the Helmholtz integral formulation of Chertok [J. Acoust. Soc. Am. 36, 1305–1313 (1964)]. Both self and mutual impedances are obtained and the admittance of each mode solved for. Finite element analysis is used to determine the mode parameters of the first 30 modes and the contribution to compliance loading of modes 7‐30. Using symmetry, the eight‐element stack is represented by a ten‐mesh circuit that includes joint compliances, end piece masses, a distributed parameter representation of the stressbar, and the contact compliances between end pieces and pistons. Input impedance and total radiated power are computed for a wide range of frequencies. For joint compliance of the order of 0.25 E–10 M/N or less, a simpler stack model is found to be adequate.

Computation of radiation impedance of stepped piston radiator

A computer program was devised for applying the Helmholz integral formulation to determine the pressure distribution on the surface of a stepped piston radiator, which consists essentially of a series of frustrums of cones and sectors of plane circles. The same program can also be used for various axially symmetrical modes of vibration of the sphere and of the plane piston by suitably specifying the values of the input parameters that determine the shape of the surface and the angle between the normal to each surface element and its direction of vibration. Good agreement is obtained (usually < 1% error) with the known analytic solutions for these latter radiators for ka⩽ 2, using only ten node from pole to equator. The complex radiation impedance as a function of ka was computed for Lubell Laboratories model 98 underwater loudspeaker that vibrates by separating along its flexible equator. The results are compared with those of a sphere that vibrates likewise. [This work was supported by Lubell Laboratorie...

Vibratory Drilling of Oil Wells

Vibratory drilling refers to the process of drilling into rock by vibrating the drilling tool at audio‐frequencies. The basic mechanism of vibratory drilling was ascertained by preliminary laboratory experimentation to consist of a series of impacts on the rock at the frequency of vibration. A fundamental study of this basic mechanism, made by dropping weighted chisels on rock, showed that the primary parameter which determined the rate of penetration was the mechanical power input to the rock per unit cross section of hole; the values of the vibration frequency and of other variables were of minor consequence over wide ranges. A theoretical analysis was made of the vibration of an elongated magnetostriction transducer capable of generating the required power level, taking into account the distributed nature of the generation of vibrations. Intermediate power transducers have been built and tested and a high‐power transducer for down‐hole operation is under construction. [The material for this presentatio...