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1
Collett, Thomas S. "Insect Navigation: Visual Panoramas and the Sky Compass." Current Biology 18, no. 22 (November 2008): R1058—R1061. http://dx.doi.org/10.1016/j.cub.2008.10.006.
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Homberg, Uwe, Stanley Heinze, Keram Pfeiffer, Michiyo Kinoshita, and Basil el Jundi. "Central neural coding of sky polarization in insects." Philosophical Transactions of the Royal Society B: Biological Sciences 366, no. 1565 (March 12, 2011): 680–87. http://dx.doi.org/10.1098/rstb.2010.0199.
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Many animals rely on a sun compass for spatial orientation and long-range navigation. In addition to the Sun, insects also exploit the polarization pattern and chromatic gradient of the sky for estimating navigational directions. Analysis of polarization–vision pathways in locusts and crickets has shed first light on brain areas involved in sky compass orientation. Detection of sky polarization relies on specialized photoreceptor cells in a small dorsal rim area of the compound eye. Brain areas involved in polarization processing include parts of the lamina, medulla and lobula of the optic lobe and, in the central brain, the anterior optic tubercle, the lateral accessory lobe and the central complex. In the optic lobe, polarization sensitivity and contrast are enhanced through convergence and opponency. In the anterior optic tubercle, polarized-light signals are integrated with information on the chromatic contrast of the sky. Tubercle neurons combine responses to the UV/green contrast and e-vector orientation of the sky and compensate for diurnal changes of the celestial polarization pattern associated with changes in solar elevation. In the central complex, a topographic representation of e-vector tunings underlies the columnar organization and suggests that this brain area serves as an internal compass coding for spatial directions.
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Zittrell, Frederick, Keram Pfeiffer, and Uwe Homberg. "Matched-filter coding of sky polarization results in an internal sun compass in the brain of the desert locust." Proceedings of the National Academy of Sciences 117, no. 41 (September 28, 2020): 25810–17. http://dx.doi.org/10.1073/pnas.2005192117.
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Many animals use celestial cues for spatial orientation. These include the sun and, in insects, the polarization pattern of the sky, which depends on the position of the sun. The central complex in the insect brain plays a key role in spatial orientation. In desert locusts, the angle of polarized light in the zenith above the animal and the direction of a simulated sun are represented in a compass-like fashion in the central complex, but how both compasses fit together for a unified representation of external space remained unclear. To address this question, we analyzed the sensitivity of intracellularly recorded central-complex neurons to the angle of polarized light presented from up to 33 positions in the animal’s dorsal visual field and injected Neurobiotin tracer for cell identification. Neurons were polarization sensitive in large parts of the virtual sky that in some cells extended to the horizon in all directions. Neurons, moreover, were tuned to spatial patterns of polarization angles that matched the sky polarization pattern of particular sun positions. The horizontal components of these calculated solar positions were topographically encoded in the protocerebral bridge of the central complex covering 360° of space. This whole-sky polarization compass does not support the earlier reported polarization compass based on stimulation from a small spot above the animal but coincides well with the previously demonstrated direct sun compass based on unpolarized light stimulation. Therefore, direct sunlight and whole-sky polarization complement each other for robust head direction coding in the locust central complex.
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Mouritsen, Henrik, and Ole Næsbye Larsen. "Migrating songbirds tested in computer-controlled Emlen funnels use stellar cues for a time-independent compass." Journal of Experimental Biology 204, no. 22 (November 15, 2001): 3855–65. http://dx.doi.org/10.1242/jeb.204.22.3855.
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SUMMARY This paper investigates how young pied flycatchers, Ficedula hypoleuca, and blackcaps, Sylvia atricapilla, interpret and use celestial cues. In order to record these data, we developed a computer-controlled version of the Emlen funnel, which enabled us to make detailed temporal analyses. First, we showed that the birds use a star compass. Then, we tested the birds under a stationary planetarium sky, which simulated the star pattern of the local sky at 02:35 h for 11 consecutive hours of the night, and compared the birds’ directional choices as a function of time with the predictions from five alternative stellar orientation hypotheses. The results supported the hypothesis suggesting that birds use a time-independent star compass based on learned geometrical star configurations to pinpoint the rotational point of the starry sky (north). In contrast, neither hypotheses suggesting that birds use the stars for establishing their global position and then perform true star navigation nor those suggesting the use of a time-compensated star compass were supported.
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Jouir, Tasarinan, Reuben Strydom, Thomas M. Stace, and Mandyam V. Srinivasan. "Vision-only egomotion estimation in 6DOF using a sky compass." Robotica 36, no. 10 (July 25, 2018): 1571–89. http://dx.doi.org/10.1017/s0263574718000577.
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SUMMARYA novel pure-vision egomotion estimation algorithm is presented, with extensions to Unmanned Aerial Systems (UAS) navigation through visual odometry. Our proposed method computes egomotion in two stages using panoramic images segmented into sky and ground regions. Rotations (in 3DOF) are estimated by using a customised algorithm to measure the motion of the sky image, which is affected only by the rotation of the aircraft, and not by its translation. The rotation estimate is then used to derotate the optic flow field generated by the ground, from which the translation of the aircraft (in 3DOF) is estimated by another customised, iterative algorithm. Segmentation of the rotation and translation estimations allows for a partial relaxation of the planar ground assumption, inherently increasing the robustness of the approach. The translation vectors are scaled using stereo-based height to compute the current UAS position through path integration for closed-loop navigation. Outdoor field tests of our approach in a small quadrotor UAS suggest that the technique is comparable to the performance of existing state-of-the-art vision-based navigation algorithms, whilst also removing all dependence on additional sensors, such as an IMU or global positioning system (GPS).
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Homberg, Uwe. "In search of the sky compass in the insect brain." Naturwissenschaften 91, no. 5 (May 1, 2004): 199–208. http://dx.doi.org/10.1007/s00114-004-0525-9.
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Müller, Martin, and Rüdiger Wehner. "Wind and sky as compass cues in desert ant navigation." Naturwissenschaften 94, no. 7 (March 15, 2007): 589–94. http://dx.doi.org/10.1007/s00114-007-0232-4.
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Kirschfeld, K. "Navigation and Compass Orientation by Insects According to the Polarization Pattern of the Sky." Zeitschrift für Naturforschung C 43, no. 5-6 (June 1, 1988): 467–69. http://dx.doi.org/10.1515/znc-1988-5-624.
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A recent theory attempts to explain how bees take their compass orientation from the pattern of polarized light in the sky (S. Rossel and R . Wehner, Nature 323, 128-131 (1986)). According to this theory, orientation can be erroneous and lead to the wrong course of a recruited bee in search of the foraging site whenever only a small patch of the blue sky is visible to the bee. It is shown that orientation under natural conditions is not erroneous, if the compass reference is variable in time but equally defined for both, scout bees and recruits.
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Kirschfeld, K. "The Role of Dorsal Rim Ommatidia in the Bee's Eye." Zeitschrift für Naturforschung C 43, no. 7-8 (August 1, 1988): 621–23. http://dx.doi.org/10.1515/znc-1988-7-823.
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A recent model of celestial e-vector analysis by the bee assumes that polarization information is transformed into modulation of perceived brightness while the bee scans the sky by rotating its field of view. It is shown that the suggested simple strategy to read compass information from the polarization pattern of the sky in natural conditions can work only in a part of the sky close to the zenith. The bee would need a different strategy for other regions of the sky.
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WEHNER, RüDIGER. "The Hymenopteran Skylight Compass: Matched Filtering and Parallel Coding." Journal of Experimental Biology 146, no. 1 (September 1, 1989): 63–85. http://dx.doi.org/10.1242/jeb.146.1.63.
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In deriving compass information from the pattern of polarized light in the sky (celestial e-vector pattern), hymenopteran insects like bees and ants accomplish a truly formidable task. Theoretically, one could solve the task by going back to first principles and using spherical geometry to compute the exact position of the sun from single patches of polarized skylight. The insect, however, does not resort to such computationally demanding solutions. Instead, during its evolutionary history, it has incorporated the fundamental spatial properties of the celestial pattern of polarization in the very periphery of its nervous system, the photoreceptor layer. There, in a specialized part of the retina (POL area), the analyser (microvillar) directions of the photoreceptors are arranged in a way that mimics the e-vector pattern in the sky {matched filtering). When scanning the sky, i.e. sweeping its matched array of analysers across the celestial e-vector pattern, the insect experiences peak responses of summed receptor outputs whenever it is aligned with the symmetry plane of the sky, which includes the solar meridian, the perpendicular from the sun to the horizon. Hence, the insect uses polarized skylight merely as a means of determining the symmetry plane of the polarization pattern, and must resort to other visual subsystems to deal with the remaining aspects of the compass problem (parallel coding). The more general message to be derived from these results is that in small brains sensory coding consists of adapting the peripheral rather than the central networks of the brain to the functional properties of the particular task to be solved. The matched peripheral networks translate the sensory information needed for performing a particular mode of behaviour into a neuronal code that can easily be understood by well-established, unspecialized central circuits. This principle of sensory coding implies that the peripheral parts of the nervous system exhibit higher evolutionary plasticity than the more central ones. Furthermore, it is reminiscent of what one observes at the cellular level of information processing, where the membrane-bound receptor molecules are specialized for particular molecular signals, but the subsequent molecular events are not. Note: Dedicated to Professor Dr Martin Lindauer in honour of his 70th birthday.
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Száz, Dénes, and Gábor Horváth. "Success of sky-polarimetric Viking navigation: revealing the chance Viking sailors could reach Greenland from Norway." Royal Society Open Science 5, no. 4 (April 2018): 172187. http://dx.doi.org/10.1098/rsos.172187.
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According to a famous hypothesis, Viking sailors could navigate along the latitude between Norway and Greenland by means of sky polarization in cloudy weather using a sun compass and sunstone crystals. Using data measured in earlier atmospheric optical and psychophysical experiments, here we determine the success rate of this sky-polarimetric Viking navigation. Simulating 1000 voyages between Norway and Greenland with varying cloudiness at summer solstice and spring equinox, we revealed the chance with which Viking sailors could reach Greenland under the varying weather conditions of a 3-week-long journey as a function of the navigation periodicity Δ t if they analysed sky polarization with calcite, cordierite or tourmaline sunstones. Examples of voyage routes are also presented. Our results show that the sky-polarimetric navigation is surprisingly successful on both days of the spring equinox and summer solstice even under cloudy conditions if the navigator determined the north direction periodically at least once in every 3 h, independently of the type of sunstone used for the analysis of sky polarization. This explains why the Vikings could rule the Atlantic Ocean for 300 years and could reach North America without a magnetic compass. Our findings suggest that it is not only the navigation periodicity in itself that is important for higher navigation success rates, but also the distribution of times when the navigation procedure carried out is as symmetrical as possible with respect to the time point of real noon.
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Freake, M. J. "Evidence for orientation using the e-vector direction of polarised light in the sleepy lizard tiliqua rugosa." Journal of Experimental Biology 202, no. 9 (May 1, 1999): 1159–66. http://dx.doi.org/10.1242/jeb.202.9.1159.
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Adult sleepy lizards (Tiliqua rugosa) were trained to orient in a predictable direction under natural sky light in outdoor pens. When tested under clear skies in the late afternoon, without a view of the sun, the lizards exhibited a symmetrical bimodal pattern of orientation with respect to the trained axis. Since the e-vector of polarised light provides an axial rather than a polar cue, the bimodal orientation exhibited by the lizards is consistent with the use of a celestial compass based on sky polarisation patterns. To confirm that the lizards could orient with respect to a polarisation pattern, lizards were trained in indoor pens to orient in a predictable direction under a linearly polarised light source. When tested in a circular arena illuminated by another polarised light source, the lizards used the e-vector direction of the polarised light source to orient along the trained axis. There was no evidence that the lizards were using any room-specific cues or brightness patterns to orient in the training direction. These results support the hypothesis that the lizards can use the e-vector direction of polarised light in the form of a sky polarisation compass.
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Frier, H., E. Edwards, C. Smith, S. Neale, and T. Collett. "Magnetic compass cues and visual pattern learning in honeybees." Journal of Experimental Biology 199, no. 6 (June 1, 1996): 1353–61. http://dx.doi.org/10.1242/jeb.199.6.1353.
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We show that honeybees can learn to distinguish between two 360 ° panoramic patterns that are identical except for their compass orientation; in this case, the difference was a 90 ° rotation about the vertical axis. To solve this task, bees must learn the patterns with respect to a directional framework. The most powerful cue to direction comes from the sky, but discrimination between patterns is possible in the absence of celestial information. Under some conditions, when other potential directional cues have been disrupted, we show that bees can use a magnetic direction to discriminate between the patterns.
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Beltrami, G., C. Bertolucci, A. Parretta, F. Petrucci, and A. Foa. "A sky polarization compass in lizards: the central role of the parietal eye." Journal of Experimental Biology 213, no. 12 (May 28, 2010): 2048–54. http://dx.doi.org/10.1242/jeb.040246.
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Bockhorst, Tobias, and Uwe Homberg. "Interaction of compass sensing and object-motion detection in the locust central complex." Journal of Neurophysiology 118, no. 1 (July 1, 2017): 496–506. http://dx.doi.org/10.1152/jn.00927.2016.
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Goal-directed behavior is often complicated by unpredictable events, such as the appearance of a predator during directed locomotion. This situation requires adaptive responses like evasive maneuvers followed by subsequent reorientation and course correction. Here we study the possible neural underpinnings of such a situation in an insect, the desert locust. As in other insects, its sense of spatial orientation strongly relies on the central complex, a group of midline brain neuropils. The central complex houses sky compass cells that signal the polarization plane of skylight and thus indicate the animal’s steering direction relative to the sun. Most of these cells additionally respond to small moving objects that drive fast sensory-motor circuits for escape. Here we investigate how the presentation of a moving object influences activity of the neurons during compass signaling. Cells responded in one of two ways: in some neurons, responses to the moving object were simply added to the compass response that had adapted during continuous stimulation by stationary polarized light. By contrast, other neurons disadapted, i.e., regained their full compass response to polarized light, when a moving object was presented. We propose that the latter case could help to prepare for reorientation of the animal after escape. A neuronal network based on central-complex architecture can explain both responses by slight changes in the dynamics and amplitudes of adaptation to polarized light in CL columnar input neurons of the system. NEW & NOTEWORTHY Neurons of the central complex in several insects signal compass directions through sensitivity to the sky polarization pattern. In locusts, these neurons also respond to moving objects. We show here that during polarized-light presentation, responses to moving objects override their compass signaling or restore adapted inhibitory as well as excitatory compass responses. A network model is presented to explain the variations of these responses that likely serve to redirect flight or walking following evasive maneuvers.
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Tang, Jun, Nan Zhang, Dalin Li, Fei Wang, Binzhen Zhang, Chenguang Wang, Chong Shen, Jianbin Ren, Chenyang Xue, and Jun Liu. "Novel robust skylight compass method based on full-sky polarization imaging under harsh conditions." Optics Express 24, no. 14 (July 5, 2016): 15834. http://dx.doi.org/10.1364/oe.24.015834.
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Able, K., and M. Able. "The flexible migratory orientation system of the savannah sparrow (Passerculus sandwichensis)." Journal of Experimental Biology 199, no. 1 (January 1, 1996): 3–8. http://dx.doi.org/10.1242/jeb.199.1.3.
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The orientation system of the Savannah sparrow (Passerculus sandwichensis) is typical of nocturnal migrant passerine birds. It is based on a system of interacting compass senses: magnetic, star, polarized light and, perhaps, sun compasses. The magnetic compass capability develops in birds that have never seen the sky, but the preferred direction of magnetic orientation may be calibrated by celestial rotation (stars at night and polarized skylight patterns during the day). This ability to recalibrate magnetic orientation persists throughout life and enables the bird to compensate for variability in magnetic declination that may be encountered as it migrates. The polarized light compass may be manipulated by exposing young birds to altered patterns of skylight polarization. There is some evidence that the magnetic field may be involved in calibration of the polarized light compass. In short-term orientation decision-making during migration, visual information at sunset overrides both stars and magnetic cues, and polarized skylight is the relevant stimulus in dusk orientation. The star pattern compass seems to be of little importance. This extremely flexible orientation system enables the birds to respond to spatial and temporal variability in the quality and availability of orientation information.
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Pfeiffer, Keram, Mario Negrello, and Uwe Homberg. "Conditional Perception Under Stimulus Ambiguity: Polarization- and Azimuth-Sensitive Neurons in the Locust Brain Are Inhibited by Low Degrees of Polarization." Journal of Neurophysiology 105, no. 1 (January 2011): 28–35. http://dx.doi.org/10.1152/jn.00480.2010.
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Sensory perception often relies on the integration and matching of multisensory inputs. In the brain of desert locusts, identified neurons that signal the sun's direction relative to the animal's head integrate information about the polarization pattern of the sky with information on the color and intensity contrast of the sky. The cloudless blue sky exhibits a gradient from unpolarized sunlight to strongly polarized light at 90° from the sun. Therefore the percentage of polarized light in the sky is highest at dusk and dawn and lowest when the sun is in the zenith. We investigated the effect of different degrees of polarization on neurons of the anterior optic tubercle of the desert locust through intracellular recordings. Whereas dorsal presentation of strongly polarized light largely excited the neurons, weakly polarized light, i.e., a blend of polarized light of many orientations, led to inhibition. The data suggest that the polarization input to these neurons is inhibited within a radius of 50° around the sun, thereby avoiding conflicting input from the polarization and direct sunlight channels. These properties can be regarded as sensory filters to avoid ambiguous signaling during sky compass orientation.
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Dacke, Marie, Emily Baird, Basil el Jundi, Eric J. Warrant, and Marcus Byrne. "How Dung Beetles Steer Straight." Annual Review of Entomology 66, no. 1 (January 7, 2021): 243–56. http://dx.doi.org/10.1146/annurev-ento-042020-102149.
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Distant and predictable features in the environment make ideal compass cues to allow movement along a straight path. Ball-rolling dung beetles use a wide range of different signals in the day or night sky to steer themselves along a fixed bearing. These include the sun, the Milky Way, and the polarization pattern generated by the moon. Almost two decades of research into these remarkable creatures have shown that the dung beetle's compass is flexible and readily adapts to the cues available in its current surroundings. In the morning and afternoon, dung beetles use the sun to orient, but at midday, they prefer to use the wind, and at night or in a forest, they rely primarily on polarized skylight to maintain straight paths. We are just starting to understand the neuronal substrate underlying the dung beetle's compass and the mystery of why these beetles start each journey with a dance.
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Bachmann, Jens, Xiaosu Yi, Konstantinos Tserpes, Carmen Sguazzo, Lucia Gratiela Barbu, Barbara Tse, Constantinos Soutis, Eric Ramón, Hector Linuesa, and Stéphane Bechtel. "Towards a Circular Economy in the Aviation Sector Using Eco-Composites for Interior and Secondary Structures. Results and Recommendations from the EU/China Project ECO-COMPASS." Aerospace 8, no. 5 (May 5, 2021): 131. http://dx.doi.org/10.3390/aerospace8050131.
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Fiber reinforced polymers play a crucial role as enablers of lightweight and high performing structures to increase efficiency in aviation. However, the ever-increasing awareness for the environmental impacts has led to a growing interest in bio-based and recycled ‘eco-composites’ as substitutes for the conventional synthetic constituents. Recently, the international collaboration of Chinese and European partners in the ECO-COMPASS project provided an assessment of different eco-materials and technologies for their potential application in aircraft interior and secondary composite structures. This project summary reports the main findings of the ECO-COMPASS project and gives an outlook to the next steps necessary for introducing eco-composites as an alternative solution to fulfill the CLEAN SKY target.
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Kraft, P., C. Evangelista, M. Dacke, T. Labhart, and M. V. Srinivasan. "Honeybee navigation: following routes using polarized-light cues." Philosophical Transactions of the Royal Society B: Biological Sciences 366, no. 1565 (March 12, 2011): 703–8. http://dx.doi.org/10.1098/rstb.2010.0203.
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While it is generally accepted that honeybees ( Apis mellifera ) are capable of using the pattern of polarized light in the sky to navigate to a food source, there is little or no direct behavioural evidence that they actually do so. We have examined whether bees can be trained to find their way through a maze composed of four interconnected tunnels, by using directional information provided by polarized light illumination from the ceilings of the tunnels. The results show that bees can learn this task, thus demonstrating directly, and for the first time, that bees are indeed capable of using the polarized-light information in the sky as a compass to steer their way to a food source.
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Gudmundsson, G. A., and R. Sandberg. "Sanderlings (Calidris alba) have a magnetic compass: orientation experiments during spring migration in Iceland." Journal of Experimental Biology 203, no. 20 (October 15, 2000): 3137–44. http://dx.doi.org/10.1242/jeb.203.20.3137.
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The migratory orientation of sanderlings (Calidris alba) was investigated with cage experiments during the spring migration in southwest Iceland. Sanderlings were exposed to 90 degrees counterclockwise-shifted magnetic fields under both clear skies and natural overcast. Clear sky control tests resulted in a northerly mean direction, in agreement with predictions based on ringing recovery data and earlier visual observations of departing flocks. Sanderlings closely followed experimental deflections of magnetic fields when tested under clear skies. Control experiments under natural overcast resulted in a bimodal distribution approximately coinciding with the magnetic north-south axis. Overcast tests did not reveal any predictable response to the experimental treatment, but instead resulted in a non-significant circular distribution. The time of orientation experiments in relation to the tidal cycle affects the motivation of the birds to depart, as shown by the lower directional scatter of headings of individuals tested within the appropriate tidal window under clear skies. Sanderlings were significantly more likely to become inactive under overcast conditions than under clear sky conditions. The results demonstrate, for the first time, that a wader species such as the sanderling possesses a magnetic compass and suggest that magnetic cues are of primary directional importance. However, overcast experiments indicate that both celestial and geomagnetic information are needed for sanderlings to realize a seasonally appropriate migratory orientation.
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Muheim, Rachel, Sissel Sjöberg, and Atticus Pinzon-Rodriguez. "Polarized light modulates light-dependent magnetic compass orientation in birds." Proceedings of the National Academy of Sciences 113, no. 6 (January 25, 2016): 1654–59. http://dx.doi.org/10.1073/pnas.1513391113.
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Magnetoreception of the light-dependent magnetic compass in birds is suggested to be mediated by a radical-pair mechanism taking place in the avian retina. Biophysical models on magnetic field effects on radical pairs generally assume that the light activating the magnetoreceptor molecules is nondirectional and unpolarized, and that light absorption is isotropic. However, natural skylight enters the avian retina unidirectionally, through the cornea and the lens, and is often partially polarized. In addition, cryptochromes, the putative magnetoreceptor molecules, absorb light anisotropically, i.e., they preferentially absorb light of a specific direction and polarization, implying that the light-dependent magnetic compass is intrinsically polarization sensitive. To test putative interactions between the avian magnetic compass and polarized light, we developed a spatial orientation assay and trained zebra finches to magnetic and/or overhead polarized light cues in a four-arm “plus” maze. The birds did not use overhead polarized light near the zenith for sky compass orientation. Instead, overhead polarized light modulated light-dependent magnetic compass orientation, i.e., how the birds perceive the magnetic field. Birds were well oriented when tested with the polarized light axis aligned parallel to the magnetic field. When the polarized light axis was aligned perpendicular to the magnetic field, the birds became disoriented. These findings are the first behavioral evidence to our knowledge for a direct interaction between polarized light and the light-dependent magnetic compass in an animal. They reveal a fundamentally new property of the radical pair-based magnetoreceptor with key implications for how birds and other animals perceive the Earth’s magnetic field.
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FUKUSHI, Tsukasa. "Navigators in the desert and navigators in the grassland. Mechanisms of normal position by sky compass." Hikaku seiri seikagaku(Comparative Physiology and Biochemistry) 13, no. 2 (1996): 116–35. http://dx.doi.org/10.3330/hikakuseiriseika.13.116.
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el Jundi, Basil, Keram Pfeiffer, and Uwe Homberg. "A Distinct Layer of the Medulla Integrates Sky Compass Signals in the Brain of an Insect." PLoS ONE 6, no. 11 (November 16, 2011): e27855. http://dx.doi.org/10.1371/journal.pone.0027855.
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Hess, D., J. Koch, and B. Ronacher. "Desert ants do not rely on sky compass information for the perception of inclined path segments." Journal of Experimental Biology 212, no. 10 (May 1, 2009): 1528–34. http://dx.doi.org/10.1242/jeb.027961.
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Tyagi, Tushar, and Sanjay Kumar Bhardwaj. "Magnetic Compass Orientation in a Palaearctic–Indian Night Migrant, the Red-Headed Bunting." Animals 11, no. 6 (May 25, 2021): 1541. http://dx.doi.org/10.3390/ani11061541.
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Red-headed buntings (Emberiza bruniceps) perform long-distance migrations within their southerly overwintering grounds and breeding areas in the northern hemisphere. Long-distance migration demands essential orientation mechanisms. The earth’s magnetic field, celestial cues, and memorization of geographical cues en route provide birds with compass knowledge during migration. Birds were tested during spring migration for orientation under natural clear skies, simulated overcast skies at natural day length and temperature, simulated overcast at 22 °C and 38 °C temperatures, and in the deflected (−120°) magnetic field. Under clear skies, the red-headed buntings were oriented NNW (north–northwest); simulated overcast testing resulted in a northerly mean direction at local temperatures as well as at 22 °C and 38 °C. The buntings reacted strongly in favor of the rotated magnetic field under the simulated overcast sky, demonstrating the use of a magnetic compass for migrating in a specific direction.
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Pomozi, István, Gábor Horváth, and Rüdiger Wehner. "How the clear-sky angle of polarization pattern continues underneath clouds: full-sky measurements and implications for animal orientation." Journal of Experimental Biology 204, no. 17 (September 1, 2001): 2933–42. http://dx.doi.org/10.1242/jeb.204.17.2933.
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SUMMARY One of the biologically most important parameters of the cloudy sky is the proportion P of the celestial polarization pattern available for use in animal navigation. We evaluated this parameter by measuring the polarization patterns of clear and cloudy skies using 180° (full-sky) imaging polarimetry in the red (650nm), green (550nm) and blue (450nm) ranges of the spectrum under clear and partly cloudy conditions. The resulting data were compared with the corresponding celestial polarization patterns calculated using the single-scattering Rayleigh model. We show convincingly that the pattern of the angle of polarization (e-vectors) in a clear sky continues underneath clouds if regions of the clouds and parts of the airspace between the clouds and the earth surface (being shady at the position of the observer) are directly lit by the sun. The scattering and polarization of direct sunlight on the cloud particles and in the air columns underneath the clouds result in the same e-vector pattern as that present in clear sky. This phenomenon can be exploited for animal navigation if the degree of polarization is higher than the perceptual threshold of the visual system, because the angle rather than the degree of polarization is the most important optical cue used in the polarization compass. Hence, the clouds reduce the extent of sky polarization pattern that is useful for animal orientation much less than has hitherto been assumed. We further demonstrate quantitatively that the shorter the wavelength, the greater the proportion of celestial polarization that can be used by animals under cloudy-sky conditions. As has already been suggested by others, this phenomenon may solve the ultraviolet paradox of polarization vision in insects such as hymenopterans and dipterans. The present study extends previous findings by using the technique of 180° imaging polarimetry to measure and analyse celestial polarization patterns.
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Stone, Thomas, Michael Mangan, Antoine Wystrach, and Barbara Webb. "Rotation invariant visual processing for spatial memory in insects." Interface Focus 8, no. 4 (June 15, 2018): 20180010. http://dx.doi.org/10.1098/rsfs.2018.0010.
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Visual memory is crucial to navigation in many animals, including insects. Here, we focus on the problem of visual homing, that is, using comparison of the view at a current location with a view stored at the home location to control movement towards home by a novel shortcut. Insects show several visual specializations that appear advantageous for this task, including almost panoramic field of view and ultraviolet light sensitivity, which enhances the salience of the skyline. We discuss several proposals for subsequent processing of the image to obtain the required motion information, focusing on how each might deal with the problem of yaw rotation of the current view relative to the home view. Possible solutions include tagging of views with information from the celestial compass system, using multiple views pointing towards home, or rotation invariant encoding of the view. We illustrate briefly how a well-known shape description method from computer vision, Zernike moments, could provide a compact and rotation invariant representation of sky shapes to enhance visual homing. We discuss the biological plausibility of this solution, and also a fourth strategy, based on observed behaviour of insects, that involves transfer of information from visual memory matching to the compass system.
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Khaldy, Lana, Orit Peleg, Claudia Tocco, L. Mahadevan, Marcus Byrne, and Marie Dacke. "The effect of step size on straight-line orientation." Journal of The Royal Society Interface 16, no. 157 (August 2019): 20190181. http://dx.doi.org/10.1098/rsif.2019.0181.
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Moving along a straight path is a surprisingly difficult task. This is because, with each ensuing step, noise is generated in the motor and sensory systems, causing the animal to deviate from its intended route. When relying solely on internal sensory information to correct for this noise, the directional error generated with each stride accumulates, ultimately leading to a curved path. In contrast, external compass cues effectively allow the animal to correct for errors in its bearing. Here, we studied straight-line orientation in two different sized dung beetles. This allowed us to characterize and model the size of the directional error generated with each step, in the absence of external visual compass cues ( motor error ) as well as in the presence of these cues ( compass and motor errors ). In addition, we model how dung beetles balance the influence of internal and external orientation cues as they orient along straight paths under the open sky. We conclude that the directional error that unavoidably accumulates as the beetle travels is inversely proportional to the step size of the insect, and that both beetle species weigh the two sources of directional information in a similar fashion.
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ABLE, KENNETH P. "Skylight Polarization Patterns and the Orientation of Migratory Birds." Journal of Experimental Biology 141, no. 1 (January 1, 1989): 241–56. http://dx.doi.org/10.1242/jeb.141.1.241.
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Patterns of polarized light present in the clear dusk sky provide directional information relevant to the orientation behaviour of migratory birds. Experiments performed with white-throated sparrows (Zonotrichia albicollis) and American tree sparrows (Spizella arborea), North American night migrants, examined migratory orientation between the time of sunset and the first appearance of stars under several manipulations of skylight polarization patterns. Under clear skies, birds tested in Emlen funnel orientation cages oriented their hopping basically parallel to the E-vector of polarized light, with a bias towards the brightest part of the sky (sunset direction). Under solid, thick overcast conditions (no polarized light from the natural sky), birds showed axially bimodal hopping orientation parallel to an imposed E-vector. When birds were tested in cages covered with depolarizing material under a clear sky, their hopping orientation was seasonally appropriate and indistinguishable from controls viewing an unaltered clear sky. Skylight polarization patterns are not necessary for the occurrence of migratory orientation, but birds respond strongly to manipulations of the E-vector direction. The results reported here support the hypothesis that the relevant stimulus is the E-vector orientation rather than other parameters of skylight, e.g. intensity or colour patterns, degree of polarization. It appears that these night migrants are using skylight polarization at dusk as one of a set of multiple compass capabilities. Because of the necessarily artificial nature of the polarized light stimuli used in the experimental manipulations, it has not been possible to establish the relationship between this orientation cue and other known mechanisms (magnetic, sun and star compasses).
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Tarng, Wernhuar, Jiong-Kai Pan, and Chiu-Pin Lin. "Development of a Motion Sensing and Automatic Positioning Universal Planisphere Using Augmented Reality Technology." Mobile Information Systems 2017 (2017): 1–13. http://dx.doi.org/10.1155/2017/3167435.
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This study combines the augmented reality technology and the sensor functions of GPS, electronic compass, and 3-axis accelerometer on mobile devices to develop a motion sensing and automatic positioning universal planisphere. It can create local star charts according to the current date, time, and position and help users locate constellations on the planisphere easily through motion sensing operation. By holding the mobile device towards the target constellation in the sky, the azimuth and elevation angles are obtained automatically for mapping to its correct position on the star chart. The proposed system combines observational activities with physical operation and spatial cognition for developing correct astronomical concepts, thus making learning more effective. It contains a built-in 3D virtual starry sky to enable observation in classroom for supporting teaching applications. The learning process can be shortened by setting varying observation date, time, and latitude. Therefore, it is a useful tool for astronomy education.
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Labhart, Thomas, Jürgen Petzold, and Hansruedi Helbling. "Spatial integration in polarization-sensitive interneurones of crickets: a survey of evidence, mechanisms and benefits." Journal of Experimental Biology 204, no. 14 (July 15, 2001): 2423–30. http://dx.doi.org/10.1242/jeb.204.14.2423.
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SUMMARY Many insects exploit the polarization pattern of the sky for compass orientation in navigation or cruising-course control. Polarization-sensitive neurones (POL1-neurones) in the polarization vision pathway of the cricket visual system have wide visual fields of approximately 60° diameter, i.e. these neurones integrate information over a large area of the sky. This results from two different mechanisms. (i) Optical integration; polarization vision is mediated by a group of specialized ommatidia at the dorsal rim of the eye. These ommatidia lack screening pigment, contain a wide rhabdom and have poor lens optics. As a result, the angular sensitivity of the polarization-sensitive photoreceptors is very wide (median approximately 20°). (ii) Neural integration; each POL1-neurone receives input from a large number of dorsal rim photoreceptors with diverging optical axes. Spatial integration in POL1-neurones acts as a spatial low-pass filter. It improves the quality of the celestial polarization signal by filtering out cloud-induced local disturbances in the polarization pattern and increases sensitivity.
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el Jundi, Basil, and Uwe Homberg. "Receptive field properties and intensity-response functions of polarization-sensitive neurons of the optic tubercle in gregarious and solitarious locusts." Journal of Neurophysiology 108, no. 6 (September 15, 2012): 1695–710. http://dx.doi.org/10.1152/jn.01023.2011.
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Many migrating insects rely on the plane of sky polarization as a cue to detect spatial directions. Desert locusts ( Schistocerca gregaria), like other insects, perceive polarized light through specialized photoreceptors in a dorsal eye region. Desert locusts occur in two phases: a gregarious swarming phase, which migrates during the day, and a solitarious nocturnal phase. Neurons in a small brain area, the anterior optic tubercle (AOTu), are critically involved in processing polarized light in the locust brain. While polarization-sensitive intertubercle cells [lobula-tubercle neuron 1 (LoTu1) and tubercle-tubercle neuron 1 (TuTu1)] interconnect the AOTu of both hemispheres, tubercle-lateral accessory lobe tract (TuLAL1) neurons transmit sky compass signals to a polarization compass in the central brain. To better understand the neural network underlying polarized light processing in the AOTu and to investigate possible adaptations of the polarization vision system to a diurnal versus nocturnal lifestyle, we analyzed receptive field properties, intensity-response relationships, and daytime dependence of responses of AOTu neurons in gregarious and solitarious locusts. Surprisingly, no differences in the physiology of these neurons were found between the two locust phases. Instead, clear differences were observed between the different types of AOTu neurons. Whereas TuTu1 and TuLAL1 neurons encoded E-vector orientation independent of light intensity and would thus be operational in bright daylight, LoTu1 neurons were inhibited by high light intensity and provided strong polarization signaling only under dim light conditions. The presence of high- and low-intensity polarization channels might, therefore, allow solitarious and gregarious locusts to use the same polarization coding system despite their different activity cycles.
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Száz, Dénes, Alexandra Farkas, András Barta, Balázs Kretzer, Miklós Blahó, Ádám Egri, Gyula Szabó, and Gábor Horváth. "Accuracy of the hypothetical sky-polarimetric Viking navigation versus sky conditions: revealing solar elevations and cloudinesses favourable for this navigation method." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 473, no. 2205 (September 2017): 20170358. http://dx.doi.org/10.1098/rspa.2017.0358.
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According to Thorkild Ramskou's theory proposed in 1967, under overcast and foggy skies, Viking seafarers might have used skylight polarization analysed with special crystals called sunstones to determine the position of the invisible Sun. After finding the occluded Sun with sunstones, its elevation angle had to be measured and its shadow had to be projected onto the horizontal surface of a sun compass. According to Ramskou's theory, these sunstones might have been birefringent calcite or dichroic cordierite or tourmaline crystals working as polarizers. It has frequently been claimed that this method might have been suitable for navigation even in cloudy weather. This hypothesis has been accepted and frequently cited for decades without any experimental support. In this work, we determined the accuracy of this hypothetical sky-polarimetric Viking navigation for 1080 different sky situations characterized by solar elevation θ and cloudiness ρ , the sky polarization patterns of which were measured by full-sky imaging polarimetry. We used the earlier measured uncertainty functions of the navigation steps 1, 2 and 3 for calcite, cordierite and tourmaline sunstone crystals, respectively, and the newly measured uncertainty function of step 4 presented here. As a result, we revealed the meteorological conditions under which Vikings could have used this hypothetical navigation method. We determined the solar elevations at which the navigation uncertainties are minimal at summer solstice and spring equinox for all three sunstone types. On average, calcite sunstone ensures a more accurate sky-polarimetric navigation than tourmaline and cordierite. However, in some special cases (generally at 35° ≤ θ ≤ 40°, 1 okta ≤ ρ ≤ 6 oktas for summer solstice, and at 20° ≤ θ ≤ 25°, 0 okta ≤ ρ ≤ 4 oktas for spring equinox), the use of tourmaline and cordierite results in smaller navigation uncertainties than that of calcite. Generally, under clear or less cloudy skies, the sky-polarimetric navigation is more accurate, but at low solar elevations its accuracy remains relatively large even at high cloudiness. For a given ρ , the absolute value of averaged peak North uncertainties dramatically decreases with increasing θ until the sign (±) change of these uncertainties. For a given θ , this absolute value can either decrease or increase with increasing ρ . The most advantageous sky situations for this navigation method are at summer solstice when the solar elevation and cloudiness are 35° ≤ θ ≤ 40° and 2 oktas ≤ ρ ≤ 3 oktas.
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Zeller, Maximilian, Martina Held, Julia Bender, Annuska Berz, Tanja Heinloth, Timm Hellfritz, and Keram Pfeiffer. "Transmedulla Neurons in the Sky Compass Network of the Honeybee (Apis mellifera) Are a Possible Site of Circadian Input." PLOS ONE 10, no. 12 (December 2, 2015): e0143244. http://dx.doi.org/10.1371/journal.pone.0143244.
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Dacke, M., M. J. Byrne, E. Baird, C. H. Scholtz, and E. J. Warrant. "How dim is dim? Precision of the celestial compass in moonlight and sunlight." Philosophical Transactions of the Royal Society B: Biological Sciences 366, no. 1565 (March 12, 2011): 697–702. http://dx.doi.org/10.1098/rstb.2010.0191.
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Prominent in the sky, but not visible to humans, is a pattern of polarized skylight formed around both the Sun and the Moon. Dung beetles are, at present, the only animal group known to use the much dimmer polarization pattern formed around the Moon as a compass cue for maintaining travel direction. However, the Moon is not visible every night and the intensity of the celestial polarization pattern gradually declines as the Moon wanes. Therefore, for nocturnal orientation on all moonlit nights, the absolute sensitivity of the dung beetle's polarization detector may limit the precision of this behaviour. To test this, we studied the straight-line foraging behaviour of the nocturnal ball-rolling dung beetle Scarabaeus satyrus to establish when the Moon is too dim—and the polarization pattern too weak—to provide a reliable cue for orientation. Our results show that celestial orientation is as accurate during crescent Moon as it is during full Moon. Moreover, this orientation accuracy is equal to that measured for diurnal species that orient under the 100 million times brighter polarization pattern formed around the Sun. This indicates that, in nocturnal species, the sensitivity of the optical polarization compass can be greatly increased without any loss of precision.
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Munro, U., and R. Wiltschko. "CLOCK-SHIFT EXPERIMENTS WITH MIGRATORY YELLOW- FACED HONEYEATERS, LICHENOSTOMUS CHRYSOPS (MELIPHAGIDAE), AN AUSTRALIAN DAY-MIGRATING BIRD." Journal of Experimental Biology 181, no. 1 (August 1, 1993): 233–44. http://dx.doi.org/10.1242/jeb.181.1.233.
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The behaviour of an Australian day migrant, the yellow-faced honeyeater Lichenostomus chrysops, was studied in order to assess the role of the sun in migratory orientation. During autumn migration, all tests took place under a sunny sky; birds were tested while living in the natural photoperiod (control) and with their internal clock shifted 4 h fast and 4 h slow. In spring, all birds were shifted 3 h fast; tests in overcast conditions, with the birds relying on their magnetic compass, served as controls. In control tests in both seasons, the birds preferred directions corresponding to those observed in the wild. When tested under sunny conditions with their internal clock shifted, the birds changed their directional tendencies. However, their preferred directions were different from those expected if a time-compensating sun compass was being used. After about 6 days, the shifted birds' directions were no longer different from the control direction. This behaviour argues against a major role of the sun compass in the orientation of day migrants. The dramatic changes of the sun's arc with geographic latitute might cause day-migrating birds to prefer a more constant orientation cue, such as the geomagnetic field. The initial response to the clock-shift might have occurred because the birds were confused by the conflicting information from solar and magnetic cues. This suggests that the sun is usually used as a secondary cue in combination with the magnetic field.
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Evangelista, C., P. Kraft, M. Dacke, T. Labhart, and M. V. Srinivasan. "Honeybee navigation: critically examining the role of the polarization compass." Philosophical Transactions of the Royal Society B: Biological Sciences 369, no. 1636 (February 19, 2014): 20130037. http://dx.doi.org/10.1098/rstb.2013.0037.
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Although it is widely accepted that honeybees use the polarized-light pattern of the sky as a compass for navigation, there is little direct evidence that this information is actually sensed during flight. Here, we ask whether flying bees can obtain compass cues derived purely from polarized light, and communicate this information to their nest-mates through the ‘waggle dance’. Bees, from an observation hive with vertically oriented honeycombs, were trained to fly to a food source at the end of a tunnel, which provided overhead illumination that was polarized either parallel to the axis of the tunnel, or perpendicular to it. When the illumination was transversely polarized, bees danced in a predominantly vertical direction with waggles occurring equally frequently in the upward or the downward direction. They were thus using the polarized-light information to signal the two possible directions in which they could have flown in natural outdoor flight: either directly towards the sun, or directly away from it. When the illumination was axially polarized, the bees danced in a predominantly horizontal direction with waggles directed either to the left or the right, indicating that they could have flown in an azimuthal direction that was 90° to the right or to the left of the sun, respectively. When the first half of the tunnel provided axial illumination and the second half transverse illumination, bees danced along all of the four principal diagonal directions, which represent four equally likely locations of the food source based on the polarized-light information that they had acquired during their journey. We conclude that flying bees are capable of obtaining and signalling compass information that is derived purely from polarized light. Furthermore, they deal with the directional ambiguity that is inherent in polarized light by signalling all of the possible locations of the food source in their dances, thus maximizing the chances of recruitment to it.
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Liang, Huaju, Hongyang Bai, Ning Liu, and Xiubao Sui. "Polarization Navigation Simulation System and Skylight Compass Method Design Based upon Moment of Inertia." Mathematical Problems in Engineering 2020 (May 13, 2020): 1–14. http://dx.doi.org/10.1155/2020/4081269.
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Unpolarized sunlight becomes polarized by atmospheric scattering and produces a skylight polarization pattern in the sky, which is detected for navigation by several species of insects. Inspired by these insects, a growing number of research studies have been conducted on how to effectively determine a heading angle from polarization patterns of skylight. However, few research studies have considered that the pixels of a pixelated polarization camera can be easily disturbed by noise and numerical values among adjacent pixels are discontinuous caused by crosstalk. So, this paper proposes a skylight compass method based upon the moment of inertia (MOI). Inspired by rigid body dynamics, the MOI of a rigid body with uniform mass distribution reaches the extreme values when the rigid body rotates on its symmetry axes. So, a whole polarization image is regarded as a rigid body. Then, orientation determination is transformed into solving the extreme value of MOI. This method makes full use of the polarization information of a whole polarization image and accordingly reduces the influence of the numerical discontinuity among adjacent pixels and measurement noise. In addition, this has been verified by numerical simulation and experiment. And the compass error of the MOI method is less than 0.44° for an actual polarization image.
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Sakura, Midori, Ryuichi Okada, and Hitoshi Aonuma. "Evidence for instantaneous e-vector detection in the honeybee using an associative learning paradigm." Proceedings of the Royal Society B: Biological Sciences 279, no. 1728 (July 6, 2011): 535–42. http://dx.doi.org/10.1098/rspb.2011.0929.
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Many insects use the polarization pattern of the sky for obtaining compass information during orientation or navigation. E-vector information is collected by a specialized area in the dorsal-most part of the compound eye, the dorsal rim area (DRA). We tested honeybees' capability of learning certain e-vector orientations by using a classical conditioning paradigm with the proboscis extension reflex. When one e-vector orientation (CS+) was associated with sugar water, while another orientation (CS−) was not rewarded, the honeybees could discriminate CS+ from CS−. Bees whose DRA was inactivated by painting did not learn CS+. When ultraviolet (UV) polarized light (350 nm) was used for CS, the bees discriminated CS+ from CS−, but no discrimination was observed in blue (442 nm) or green light (546 nm). Our data indicate that honeybees can learn and discriminate between different e-vector orientations, sensed by the UV receptors of the DRA, suggesting that bees can determine their flight direction from polarized UV skylight during foraging. Fixing the bees' heads during the experiments did not prevent learning, indicating that they use an ‘instantaneous’ algorithm of e-vector detection; that is, the bees do not need to actively scan the sky with their DRAs (‘sequential’ method) to determine e-vector orientation.
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GAO, JUN, LEI WANG, MEI BO, and ZHIGUO FAN. "INFORMATION ACQUISITION IN DESERT ANT NAVIGATION." International Journal of Information Acquisition 03, no. 01 (March 2006): 33–43. http://dx.doi.org/10.1142/s0219878906000800.
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Desert ant (Cataglyphis) is famous for its ability in navigation. In deserts with very few visual and odor information, the ant can return to its den almost along a straight line after foraging away in a distance of much more than thousands of times longer than its body length. Several kinds of information must be acquired during its trip, and the most important two are: path integration and visual navigation. Path integration is achieved by using sky light compass based on polarized light and odometer, while visual navigation relies on landmark based memory and matching. In this paper, a survey of research work on desert ant navigation from the viewpoint of information acquisition and fusion is presented, as well as the application of these kinds of information to navigate robots, especially bionic robots cruising in strange environment.
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Coemans, M., J. Hzn, and J. Nuboer. "THE ORIENTATION OF THE E-VECTOR OF LINEARLY POLARIZED LIGHT DOES NOT AFFECT THE BEHAVIOUR OF THE PIGEON COLUMBA LIVIA." Journal of Experimental Biology 191, no. 1 (June 1, 1994): 107–23. http://dx.doi.org/10.1242/jeb.191.1.107.
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Orientation with reference to the time-compensated sun-azimuth compass has been established for the homing pigeon Columba livia. Previous qualitative studies claim that pigeons are sensitive to the orientation of a polarizer and it has been suggested that these animals are able to use sky-light polarization as an indirect reference to the sun's position when the latter is shielded from view. We report experiments which were undertaken to quantify the sensitivity of the homing pigeon to the orientation of linearly polarized light. The results of our initial experiments suggested that the animals responded to secondary cues. Further experiments were carried out to avoid such artefacts. Under circumstances where secondary cues were rigorously avoided, we were, however, not able to demonstrate any directional response that was caused by the E-vector orientation of the illumination. These results throw doubt on the suggested polarization-sensitivity of birds in general.
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Sandberg, R., and J. Pettersson. "Magnetic orientation of snow buntings (Plectrophenax nivalis), a species breeding in the high Arctic: passage migration through temperate-zone areas." Journal of Experimental Biology 199, no. 9 (September 1, 1996): 1899–905. http://dx.doi.org/10.1242/jeb.199.9.1899.
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Orientation tests were conducted with snow buntings (Plectrophenax nivalis) exposed to artificially manipulated magnetic fields, during both spring and autumn migration. Experiments were run under clear sunset skies and under simulated complete overcast. The birds closely followed experimental shifts of the magnetic fields during both seasons regardless of whether they had access to celestial cues. Clear-sky tests in vertical magnetic fields resulted in a significant bimodal orientation, the directionality of which was almost identical during spring and autumn. When the snow buntings were deprived of celestial directional information and tested in vertical magnetic fields, they failed to show any statistically significant mean directions in either spring or autumn. The results demonstrate that snow buntings possess a magnetic compass and suggest that magnetic cues are of primary importance for their migratory orientation while on passage through temperate-zone areas. However, the axial orientation in vertical magnetic fields under clear skies may indicate an involvement of celestial cues as an auxiliary source of directional information.
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Pfeiffer, Keram, Michiyo Kinoshita, and Uwe Homberg. "Polarization-Sensitive and Light-Sensitive Neurons in Two Parallel Pathways Passing Through the Anterior Optic Tubercle in the Locust Brain." Journal of Neurophysiology 94, no. 6 (December 2005): 3903–15. http://dx.doi.org/10.1152/jn.00276.2005.
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Many migrating animals use a sun compass for long-range navigation. One of the guiding cues used by insects is the polarization pattern of the blue sky. In the desert locust Schistocerca gregaria, neurons of the central complex, a neuropil in the center of the brain, are sensitive to polarized light and might serve a key role in compass navigation. Visual pathways to the central complex include signal processing in the upper and lower units of the anterior optic tubercle. To determine whether these pathways carry polarization-vision signals, we have recorded the responses of interneurons of the optic tubercle of the locust to visual stimuli including polarized light. All neurons of the lower unit but only one of five recorded neurons of the upper unit of the tubercle were sensitive to linearly polarized light presented in the dorsal visual field. These neurons showed polarization opponency, or a sinusoidal modulation of activity, during stimulation through a rotating polarizer. Two types of bilateral interneurons preferred particular e-vector orientations, reflecting the presence of bilateral pairs of these neurons in the brain. We show here for the first time neurons with projections to the lateral accessory lobe that are suited to provide polarization input to the central complex. All neurons of the tubercle, furthermore, responded to unpolarized light, mostly with tonic activity changes. These responses strongly depended on stimulus position and might reflect navigation-relevant signals such as direct sunlight or visual landmarks that are integrated with polarization responses in neurons of the lower unit.
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Bockhorst, Tobias, and Uwe Homberg. "Amplitude and dynamics of polarization-plane signaling in the central complex of the locust brain." Journal of Neurophysiology 113, no. 9 (May 2015): 3291–311. http://dx.doi.org/10.1152/jn.00742.2014.
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The polarization pattern of skylight provides a compass cue that various insect species use for allocentric orientation. In the desert locust, Schistocerca gregaria, a network of neurons tuned to the electric field vector ( E-vector) angle of polarized light is present in the central complex of the brain. Preferred E-vector angles vary along slices of neuropils in a compasslike fashion (polarotopy). We studied how the activity in this polarotopic population is modulated in ways suited to control compass-guided locomotion. To this end, we analyzed tuning profiles using measures of correlation between spike rate and E-vector angle and, furthermore, tested for adaptation to stationary angles. The results suggest that the polarotopy is stabilized by antagonistic integration across neurons with opponent tuning. Downstream to the input stage of the network, responses to stationary E-vector angles adapted quickly, which may correlate with a tendency to steer a steady course previously observed in tethered flying locusts. By contrast, rotating E-vectors corresponding to changes in heading direction under a natural sky elicited nonadapting responses. However, response amplitudes were particularly variable at the output stage, covarying with the level of ongoing activity. Moreover, the responses to rotating E-vector angles depended on the direction of rotation in an anticipatory manner. Our observations support a view of the central complex as a substrate of higher-stage processing that could assign contextual meaning to sensory input for motor control in goal-driven behaviors. Parallels to higher-stage processing of sensory information in vertebrates are discussed.
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Schmitt, Franziska, Sara Mae Stieb, Rüdiger Wehner, and Wolfgang Rössler. "Experience-related reorganization of giant synapses in the lateral complex: Potential role in plasticity of the sky-compass pathway in the desert antCataglyphis fortis." Developmental Neurobiology 76, no. 4 (July 14, 2015): 390–404. http://dx.doi.org/10.1002/dneu.22322.
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el Jundi, Basil, James J. Foster, Marcus J. Byrne, Emily Baird, and Marie Dacke. "Spectral information as an orientation cue in dung beetles." Biology Letters 11, no. 11 (November 2015): 20150656. http://dx.doi.org/10.1098/rsbl.2015.0656.
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During the day, a non-uniform distribution of long and short wavelength light generates a colour gradient across the sky. This gradient could be used as a compass cue, particularly by animals such as dung beetles that rely primarily on celestial cues for orientation. Here, we tested if dung beetles can use spectral cues for orientation by presenting them with monochromatic (green and UV) light spots in an indoor arena. Beetles kept their original bearing when presented with a single light cue, green or UV, or when presented with both light cues set 180° apart. When either the UV or the green light was turned off after the beetles had set their bearing in the presence of both cues, they were still able to maintain their original bearing to the remaining light. However, if the beetles were presented with two identical green light spots set 180° apart, their ability to maintain their original bearing was impaired. In summary, our data show that ball-rolling beetles could potentially use the celestial chromatic gradient as a reference for orientation.
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Weindler, P., M. Baumetz, and W. Wiltschko. "The direction of celestial rotation influences the development of stellar orientation in young garden warblers (Sylvia borin)." Journal of Experimental Biology 200, no. 15 (January 1, 1997): 2107–13. http://dx.doi.org/10.1242/jeb.200.15.2107.
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The study presented here was conducted in order to analyze the role of the direction of celestial rotation in the development of stellar orientation in young migratory birds. The test birds were garden warblers, Sylvla borin, which leave their breeding ground on a southwesterly compass course. The birds were hand-raised and, during the premigratory period, exposed to an artificial 'sky' in the local geomagnetic field. For the control group C, the star pattern was rotating in the natural direction, with the centre of rotation and magnetic North coinciding. For the three experimental groups, the star pattern was rotating in the opposite direction; for group E1, the centre of rotation coincided with magnetic North, for group E2 the centre of rotation was at magnetic West and for group E3 it was at magnetic East. During autumn migration, the birds were tested without magnetic information under the same, now stationary, sky. All four groups were able to use stellar information for orientation, but only the control group preferred the normal southwesterly course. The three experimental groups, in contrast, all oriented towards a significantly different direction, preferring due south. The results for group E1 showed less scatter than those for the other two experimental groups. These results indicate that the direction of celestial rotation is crucial for the development of the normal migratory course with respect to the stars in young garden warblers. Establishing the species-specific southwesterly migratory course requires an interaction between celestial rotation and magnetic cues; this interaction appears to depend on the natural direction of celestial rotation. Rotation in the reverse direction allowed the birds to respond only in a manner that oriented them away from the centre of rotation.
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Lerner, Amit, Shai Sabbah, Carynelisa Erlick, and Nadav Shashar. "Navigation by light polarization in clear and turbid waters." Philosophical Transactions of the Royal Society B: Biological Sciences 366, no. 1565 (March 12, 2011): 671–79. http://dx.doi.org/10.1098/rstb.2010.0189.
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Certain terrestrial animals use sky polarization for navigation. Certain aquatic species have also been shown to orient according to a polarization stimulus, but the correlation between underwater polarization and Sun position and hence the ability to use underwater polarization as a compass for navigation is still under debate. To examine this issue, we use theoretical equations for per cent polarization and electric vector (e-vector) orientation that account for the position of the Sun, refraction at the air–water interface and Rayleigh single scattering. The polarization patterns predicted by these theoretical equations are compared with measurements conducted in clear and semi-turbid coastal sea waters at 2 m and 5 m depth over sea floors of 6 m and 28 m depth. We find that the per cent polarization is correlated with the Sun's elevation only in clear waters. We furthermore find that the maximum value of the e-vector orientation angle equals the angle of refraction only in clear waters, in the horizontal viewing direction, over the deeper sea floor. We conclude that navigation by use of underwater polarization is possible under restricted conditions, i.e. in clear waters, primarily near the horizontal viewing direction, and in locations where the sea floor has limited effects on the light's polarization.