Migration along orthodromic sun compass routes by arctic birds

Flight directions of birds migrating at high geographic and magnetic latitudes can be used to test bird orientation by celestial or geomagnetic compass systems under polar conditions. Migration patterns of arctic shorebirds, revealed by tracking radar studies during an icebreaker expedition along the Northwest Passage in 1999, support predicted sun compass trajectories but cannot be reconciled with orientation along either geographic or magnetic loxodromes (rhumb lines). Sun compass routes are similar to orthodromes (great circle routes) at high latitudes, showing changing geographic courses as the birds traverse longitudes and their internal clock gets out of phase with local time. These routes bring the shorebirds from high arctic Canada to the east coast of North America, from which they make transoceanic flights to South America. The observations are also consistent with a migration link between Siberia and the Beaufort Sea region by way of sun compass routes across the Arctic Ocean.     

Navigation of single homing pigeons: airplane observations by radio tracking

Navigation of homing pigeons was investigated by tracking their homeward flights from a light airplane. Released on successive days from a single training point 35 miles (56 kilometers) from home, individual pigeons, each carrying a transmitter, were repeatedly tracked back to theirloft. No two tracks covered the same ground for even short distances, yet all tracks were within 10 miles of a straight line. Results from further releases north and south of the training point suggest that pigeons often use three methods in sequence to find home: compass orientation, bi-coordinate navigation, and orientation by familiar landmarks.     

Magnetic compass of European robins

The magnetic compass of European robins does not use the polarity of the magnetic field for detecting the north direction. The birds derive their north direction from interpreting the inclination of the axial direction of the magnetic field lines in space, and they take the direction on the magnetic north-south axis for "north" where field lines and gravity vector form the smaller angle.     

Migrating songbirds recalibrate their magnetic compass daily from twilight cues

Night migratory songbirds can use stars, sun, geomagnetic field, and polarized light for orientation when tested in captivity. We studied the interaction of magnetic, stellar, and twilight orientation cues in free-flying songbirds. We exposed Catharus thrushes to eastward-turned magnetic fields during the twilight period before takeoff and then followed them for up to 1100 kilometers. Instead of heading north, experimental birds flew westward. On subsequent nights, the same individuals migrated northward again. We suggest that birds orient with a magnetic compass calibrated daily from twilight cues. This could explain how birds cross the magnetic equator and deal with declination.     

Polarized light cues underlie compass calibration in migratory songbirds

Migratory songbirds use the geomagnetic field, stars, the Sun, and polarized light patterns to determine their migratory direction. To prevent navigational errors, it is necessary to calibrate all of these compass systems to a common reference. We show that migratory Savannah sparrows use polarized light cues from the region of sky near the horizon to recalibrate the magnetic compass at both sunrise and sunset. We suggest that skylight polarization patterns are used to derive an absolute (i.e., geographic) directional system that provides the primary calibration reference for all of the compasses of migratory songbirds.     

Lodestone Compass: Chinese or Olmec Primacy?: Multidisciplinary analysis of an Olmec hematite artifact from San Lorenzo, Veracruz, Mexico

Considering the unique morphology (purposefully shaped polished bar with a groove) and composition (magnetic mineral with magnetic moment vector in the floating plane) of M-160, and acknowledging that the Olmec were a sophisticated people who possessed advanced knowledge and skill in working iron ore minerals, I would suggest for consideration that the Early Formative artifact M-160 was probably manufactured and used as what I have called a zeroth-order compass, if not a first-order compass. The data I have presented in this article support this hypothesis, although they are not sufficient to prove it. That M-160 could be used today as a geomagnetically directed pointer is undeniable. The original whole bar may indeed have pointed close to magnetic north-south. The groove functions well as a sighting mark, and the slight angle it makes with the axis of the bar appears to be the result of calibration rather than accident. A negative supporting argument is that M-160 looks utilitarian rather than decorative, and no function for the object other than that of a compass pointer has been suggested by anyone who has examined it critically. Whether such a pointer would have been used to point to something astronomical (zeroth-order compass) or to geomagnetic north-south (first-order compass) is entirely open to speculation. The observation of the family of Olmec site alignments 8 degrees west of north is a curiosity in its own right, and the possibility that these alignments have an astronomical or geomagnetic origin should be explored. I also believe that it is constructive to compare the first millennium Chinese, who used the lodestone compass for geomancy, with the Gulf Coast Olmec since both were agrarian-terrestrial societies. The Olmec's apparent concern with orientation and skillful use of magnetic minerals also stimulates one to draw cross-cultural parallels. The evidence and analysis offered in this article provide a basis for hypotheses of parallel cultural developments in China and the Olmec New World. If the Olmec did discover the geomagnetic orienting properties of lodestone, as did the Han Chinese, it is most reasonable to speculate that they would have used their compass for comparable geomantic purposes. It should, however, be recognized that the Olmec claim, if documented, predates the Chinese discovery of the geomagnetic lodestone compass by more than a millennium. At present, M-160 is a unique artifact and San Lorenzo a unique site: "The first civilized center of Mesoamerica and probably of the New World" (19, p. 89). Further documentation of the Olmec claim must await the discovery of similar artifacts in museums, private collections, or as yet undiscovered Olmec sites. I would welcome communications from anyone possessing information relating to such artifacts. Regardless of shape, purposefully grooved and highly polished specimens of magnetic minerals are of particular interest. It would also be useful for the archeologist excavating Olmec burials and offerings to carefully note their alignments and consider them in a geomantic context. In addition to the discovery of supporting artifacts, establishment of Olmec primacy of the lodestone compass depends on the acquisition of the archeomagnetic data for the Early Formative period. I appeal to archeologists who find good archeomagnetic samples (burned hearths and post-holes) from the Formative periods to convey this information to R. DuBois of the University of Oklahoma. In a few years, the archeomagnetic data should be available for the last three millennia and the possibilities are very exciting.     

Deflection of the interstellar neutral hydrogen flow across the heliospheric interface

Using an absorption cell, we measured the Doppler shifts of the interstellar hydrogen resonance glow to show the direction of the neutral hydrogen flow as it enters the inner heliosphere. The neutral hydrogen flow is found to be deflected relative to the helium flow by about 4 degrees . The most likely explanation of this deflection is a distortion of the heliosphere under the action of an ambient interstellar magnetic field. In this case, the helium flow vector and the hydrogen flow vector constrain the direction of the magnetic field and act as an interstellar magnetic compass.     

Neural correlates of a magnetic sense

Many animals rely on Earth's magnetic field for spatial orientation and navigation. However, how the brain receives and interprets magnetic field information is unknown. Support for the existence of magnetic receptors in the vertebrate retina, beak, nose, and inner ear has been proposed, and immediate gene expression markers have identified several brain regions activated by magnetic stimulation, but the central neural mechanisms underlying magnetoreception remain unknown. Here we describe neuronal responses in the pigeon's brainstem that show how single cells encode magnetic field direction, intensity, and polarity; qualities that are necessary to derive an internal model representing directional heading and geosurface location. Our findings demonstrate that there is a neural substrate for a vertebrate magnetic sense.     

Terrestrial and aquatic orientation in the starhead topminnow, fundulus notti

Starhead topminnows from various shores of a small woodland pond were displaced to unfamiliar surroundings, and their orientation was tested in aquatic and terrestrial arenas. These fish used a sun compass to move in a direction which, at the location of their capture, would have returned them to the land-water interface. The fish accomplished directional terrestrial locomotion by using the position of the sun to align its body for each jump. On heavily overcast days many fish were unable to orient their bodies in a consistent direction from, jump to jump; this inability to orient resulted in random rather than linear movement. There was considerable individual variation in terrestrial locomotor ability.     

磁罗经数字转换器的设计

磁罗经作为低价而性能稳定的船用设备得到了大多数船只的配置应用,由于磁罗经通常安装在船头露天的地方,在使用时不太方便。磁罗经数字转换器使用固态磁阻传感器将磁罗经的磁针方位角转换成数字量的角度信号,利用单片机处理并传送到雷达或电子海图仪等设备上,从而实现航向角等航行信息的综合集中显示。磁罗经数字转换器可提供分辨率小于1°的航向角,不但可用在船上作为航行信息集中显示的辅助产品,也可以单独作为数字式电子指南针使用。     

Orientation by pigeons: is the sun necessary?

Although most recent hypotheses of pigeon homing have assigned an essential role to the sun, there has been some evidence suggesting that the sun is not essential. Two series of releases were designed to examine the question more carefully. Birds whose internal clocks had been shifted 6 hours were used in the critical tests. Under sun, the vanishing bearings of the clock-shifted birds were deflected in the direction predicted by a hypothesis of use of the sun as a simple compass. By contrast, under total overcast the bearings of both the clock-shifted and the control birds were homeward oriented and there was no difference between them, even at a release site the birds could never have seen previously. Therefore it is concluded that the sun is used as a compass when it is available, but that the pigeon navigation system contains sufficient redundancy to make accurate orientation possible in the absence of both the sun and familiar landmarks; the orientational cues used under such conditions do not require time compensation. This conclusion is in complete disagreement with the Matthews sun-arc hypothesis of pigeon navigation, and it makes necessary a major reformulation (at the very least) of the other principal hypothesis, that of Kramer.     

Conflicting evidence about long-distance animal navigation

Because of conflicting evidence about several fundamental issues, long-distance animal navigation has yet to be satisfactorily explained. Among the unsolved problems are the nature of genetic spatial control of migration and the relationships between celestial and magnetic compass mechanisms and between different map-related cues in orientation and homing, respectively. In addition, navigation is expected to differ between animal groups depending on sensory capabilities and ecological conditions. Evaluations based on modern long-term tracking techniques of the geometry of migration routes and individual migration history, combined with behavioral experiments and exploration of the sensory and genetic mechanisms, will be crucial for understanding the spatial principles that guide animals on their global journeys.     

The orientation of the local interstellar magnetic field

The orientation of the local interstellar magnetic field introduces asymmetries in the heliosphere that affect the location of heliospheric radio emissions and the streaming direction of ions from the termination shock of the solar wind. We combined observations of radio emissions and energetic particle streaming with extensive three-dimensional magnetohydrodynamic computer simulations of magnetic field draping over the heliopause to show that the plane of the local interstellar field is approximately 60 degrees to 90 degrees from the galactic plane. This finding suggests that the field orientation in the Local Interstellar Cloud differs from that of a larger-scale interstellar magnetic field thought to parallel the galactic plane.     

Magnetic direction finding: evidence for its use in migratory indigo buntings

The orientational capabilities of caged migratory indigo buntings were studied under differing magnetic field conditions. When tested in a situation allowing minimal exposure to visual cues but in the presence of the normal geomagnetic field, the birds demonstrated a significant orientation in the appropriate migratory direction (to the north). When the horizontal component of the magnetic field was deflected clockwise 120 degrees by activation of Helmholtz coils surrounding the cage, the orientation of the buntings shifted accordingly (clockwise to geographic east-southeast). These results suggest that indigo buntings are not only able to detect the geomagnetic field, but also can use this information in the finalization of their migratory direction.     

Oceili: a celestial compass in the desert ant cataglyphis

In addition to multifaceted lateral compound eyes, most insects possess three frontal eyes called ocelli. Each ocellus has a single lens, as does the vertebrate eye. The ocelli of some flying insects, locusts and dragonflies, have been shown to function as horizon detectors involved in the visual stabilization of course. In a walking insect, the desert ant Cataglyphis, it is now shown that the ocelli can read compass information from the blue sky. When the ant's compound eyes are occluded and both sun and landmarks are obscured, the ocelli, using the pattern of polarized light in the sky as a compass cue, help in guiding the ant back home.     

Mercury content of equisetum plants around mount st. Helens one year after the major eruption

The mercury content of young Equisetum plants collected around Mount St. Helens was higher in the direction of Yakima and Toppenish, Washington (northeast to east-northeast), than at any other compass heading and was about 20 times that measured around Portland, Oregon. The increase in substratum mercury was not as pronounced as that in plants but was also higher toward the northeast, the direction taken by the May 1980 volcanic plume.     

三维前方交会法测量树高及其精度分析

为了解决森林调查中因地形起伏不能通过皮尺或者视距法获得测站与目标树的水平距离,而导致不能通过一般三角测量的办法来测量树高的问题,该文将测量高程的前方交会法应用到测树上来获得树高数据.前方交会法的内容为两台仪器与目标树构成一个三角形,测量两台仪器中心的斜距和三个夹角,利用正弦定理推算目标树与一台仪器的水平距离,然后再测得树顶和树根两处的天顶距,利用三角测量获得树高.经纬仪和罗盘仪是森林调查中常用的工具,通过对该模型的精度分析和实验发现经纬仪采用此方法可以控制误差在5%以内,满足林业上的测量要求,而罗盘仪采用此方法误差范围超过5%,不能满足要求.此方法可以配合经纬仪进行树高测量.     

Maplike representation of celestial E-vector orientations in the brain of an insect

For many insects, the polarization pattern of the blue sky serves as a compass cue for spatial navigation. E-vector orientations are detected by photoreceptors in a dorsal rim area of the eye. Polarized-light signals from both eyes are finally integrated in the central complex, a brain area consisting of two subunits, the protocerebral bridge and the central body. Here we show that a topographic representation of zenithal E-vector orientations underlies the columnar organization of the protocerebral bridge in a locust. The maplike arrangement is highly suited to signal head orientation under the open sky.     

Radio tracking of homing bats

Neotropical bats, Phyllostomas hastatus, were released 10 kilometers from their home roost, and their homeward flights were tracked by radio. Flights of bats with unimpeded vision were strongly oriented in the homeward direction, while the flights of blindfolded bats did not show this marked orientation.