How Do Tiger Moths Jam Bat Sonar?

The tiger moth Bertholdia trigona is the only animal in nature known to defend itself by jamming the sonar of its predators – bats. In this study we analyzed the three-dimensional flight paths and echolocation behavior of big brown bats (Eptesicus fuscus) attacking B. trigona in a flight room over seven consecutive nights to determine the acoustic mechanism of the sonar-jamming defense. Three mechanisms have been proposed: (1) the phantom echo hypothesis, which states that bats misinterpret moth clicks as echoes; (2) the ranging interference hypothesis, which states that moth clicks degrade the bats\u27 precision in determining target distance; and (3) the masking hypothesis, which states that moth clicks mask the moth echoes entirely, making the moth temporarily invisible. On nights one and two of the experiment, the bats appeared startled by the clicks; however, on nights three through seven, the bats frequently missed their prey by a distance predicted by the ranging interference hypothesis (∼15–20 cm). Three-dimensional simulations show that bats did not avoid phantom targets, and the bats\u27 ability to track clicking prey contradicts the predictions of the masking hypothesis. The moth clicks also forced the bats to reverse their stereotyped pattern of echolocation emissions during attack, even while bats continued pursuit of the moths. This likely further hinders the bats\u27 ability to track prey. These results have implications for the evolution of sonar jamming in tiger moths, and we suggest evolutionary pathways by which sonar jamming may have evolved from other tiger moth defense mechanisms

Wake structure and kinematics in two insectivorous bats

We compare kinematics and wake structure over a range of flight speeds (4.0–8.2 m s(−1)) for two bats that pursue insect prey aerially, Tadarida brasiliensis and Myotis velifer. Body mass and wingspan are similar in these species, but M. velifer has broader wings and lower wing loading. By using high-speed videography and particle image velocimetry of steady flight in a wind tunnel, we show that three-dimensional kinematics and wake structure are similar in the two species at the higher speeds studied, but differ at lower speeds. At lower speeds, the two species show significant differences in mean angle of attack, body–wingtip distance and sweep angle. The distinct body vortex seen at low speed in T. brasiliensis and other bats studied to date is considerably weaker or absent in M. velifer. We suggest that this could be influenced by morphology: (i) the narrower thorax in this species probably reduces the body-induced discontinuity in circulation between the two wings and (ii) the wing loading is lower, hence the lift coefficient required for weight support is lower. As a result, in M. velifer, there may be a decreased disruption in the lift generation between the body and the wing, and the strength of the characteristic root vortex is greatly diminished, both suggesting increased flight efficiency. This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight’

Tracking-Reconstruction or Reconstruction-Tracking?

We developed two methods for tracking multiple objects using several camera views. The methods use the Multiple Hypothesis Tracking (MHT) framework to solve both the across-view data association problem (i.e., finding object correspondences across several views) and the across-time data association problem (i.e., the assignment of current object measurements to previously established object tracks). The "tracking-reconstruction method" establishes two-dimensional (2D) objects tracks for each view and then reconstructs their three-dimensional (3D) motion trajectories. The "reconstruction-tracking method" assembles 2D object measurements from all views, reconstructs 3D object positions, and then matches these 3D positions to previously established 3D object tracks to compute 3D motion trajectories. For both methods, we propose techniques for pruning the number of association hypotheses and for gathering track fragments. We tested and compared the performance of our methods on thermal infrared video of bats using several performance measures. Our analysis of video sequences with different levels of densities of flying bats reveals that the reconstruction-tracking method produces fewer track fragments than the tracking-reconstruction method but creates more false positive 3D tracks

Tracking-Reconstruction or Reconstruction-Tracking? Comparison of Two Multiple Hypothesis Tracking Approaches to Interpret 3D Object Motion from Several Camera Views

We developed two methods for tracking multiple objects using several camera views. The methods use the Multiple Hypothesis Tracking (MHT) framework to solve both the across-view data association problem (i.e., finding object correspondences across several views) and the across-time data association problem (i.e., the assignment of current object measurements to previously established object tracks). The “tracking-reconstruction method ” establishes two-dimensional (2D) objects tracks for each view and then reconstructs their three-dimensional (3D) motion trajectories. The “reconstruction-tracking method ” assembles 2D object measurements from all views, reconstructs 3D object positions, and then matches these 3D positions to previously established 3D object tracks to compute 3D motion trajectories. For both methods, we propose techniques for pruning the number of association hypotheses and for gathering track fragments. We tested and compared the performance of our methods on thermal infrared video of bats using several performance measures. Our analysis of video sequences with different levels of densities of flying bats reveals that the reconstruction-tracking method produces fewer track fragments than the trackingreconstruction method but creates more false positive 3D tracks. 1

Meeting visitor interest to advance conservation: A study from Indiana Dunes National Park, USA

Thousands of visitors to parks take part in ranger-led programs annually. During these programs rangers work to evoke and maintain interest in order to connect visitors with cultural and natural resources. Researchers have found interest is a powerful driver of learning, yet its role in the experience of adults who participate in ranger-led programming has not been well studied. Open-ended telephone interviews conducted months after a ranger-led hike to a prominent dune in Indiana Dunes National Park illustrate the extent to which visitors’ recollections show continuity with their reasons for attending the ranger-led hike and their uptake of resource messages. Like other ranger-led programming, this hike was designed to make intellectual and emotional connections, to fuel long-held interests, and activate new stewards. The program was the result of collaboration among rangers and local scientists. Responses to a pre-hike survey were matched with post-hike recollections transcribed following an open-ended phone interview. The vast majority of post-hike interviews revealed a match between hike participants’ initial interests and recollected details of the experience as well as new areas of piqued interest. In post-hike reflections, visitors mentioned factors that influenced the dune’s formation, and the majority mentioned the problems caused by trampling. Participants recruited for this study grasped and recollected resource messages connected to their interests. They spoke of the need to protect a popular and puzzling geological formation

M.: Tracking a large number of objects from multiple views

We propose a multi-object multi-camera framework for tracking large numbers of tightly-spaced objects that rapidly move in three dimensions. We formulate the problem of finding correspondences across multiple views as a multidimensional assignment problem and use a greedy randomized adaptive search procedure to solve this NPhard problem efficiently. To account for occlusions, we relax the one-to-one constraint that one measurement corresponds to one object and iteratively solve the relaxed assignment problem. After correspondences are established, object trajectories are estimated by stereoscopic reconstruction using an epipolar-neighborhood search. We embedded our method into a tracker-to-tracker multi-view fusion system that not only obtains the three-dimensional trajectories of closely-moving objects but also accurately settles track uncertainties that could not be resolved from single views due to occlusion. We conducted experiments to validate our greedy assignment procedure and our technique to recover from occlusions. We successfully track hundreds of flying bats and provide an analysis of their group behavior based on 150 reconstructed 3D trajectories. 1

Noise Distracts Foraging Bats

Predators frequently must detect and localize their prey in challenging environments. Noisy environments have been prevalent across the evolutionary history of predator–prey relationships, but now with increasing anthropogenic activities noise is becoming a more prominent feature of many landscapes. Here, we use the gleaning pallid bat, Antrozous pallidus, to investigate the mechanism by which noise disrupts hunting behaviour. Noise can primarily function to mask—obscure by spectrally overlapping a cue of interest, or distract—occupy an animal\u27s attentional or other cognitive resources. Using band-limited white noise treatments that either overlapped the frequencies of a prey cue or did not overlap this cue, we find evidence that distraction is a primary driver of reduced hunting efficacy in an acoustically mediated predator. Under exposure to both noise types successful prey localization declined by half, search time nearly tripled, and bats used 25% more sonar pulses than when hunting in ambient conditions. Overall, the pallid bat does not seem capable of compensating for environmental noise. These findings have implications for mitigation strategies, specifically the importance of reducing sources of noise on the landscape rather than attempting to reduce the bandwidth of anthropogenic noise

Reconstruction and analysis of 3D trajectories of Brazilian free-tailed bats in flight

The Brazilian free-tailed bat, Tadarida brasiliensis, roosts in very large colonies, consisting of hundreds of thousands of individuals. Each night, bats emerge from their day roosts in dense columns in a highly coordinated manner. We recorded short segments of an emergence using three spatially-calibrated and temporally-synchronized thermal infrared cameras. We applied stereoscopic methods to reconstruct the three-dimensional positions of these flying bats. We applied a multiple hypothesis tracking algorithm to obtain 7,016 reconstructed trajectories. Our analysis includes estimates of the velocities of bats in flight, the distances between animals within the emergence column, and the angles subtended by the bats and their nearest neighbors. 2. Methods We analyzed the nightly emergence behavior of a colony of Brazilian free-tailed bats at a cave in Texas. We used three thermal infrared FLIR SC6000 cameras that recorded 16 bit video at a resolution of 640 x 512 pixels at 125 frames per second. Example frames of video containing approximately 100 bats are shown in Figure 1. 1