Geomagnetic Position Fixing

概述拟议的研究将调查脊椎动物使用地球磁场的倾斜或“倾角”（定义为磁场线和重力之间的角度）的梯度来确定地理（“地图”）位置的能力。 以往的归航定向研究表明，磁倾角可以用来推导导航地图的一个坐标。 为了对磁倾角在提供地图信息中的作用提供更严格的测试，将使用磁倾角的小变化对归巢定向的影响来估计动物的归巢范围内的磁倾角的局部梯度的特性，例如，倾斜度的“原始值”和坡度的对齐。 然后将这些行为推导出的估计值与通过绘制动物采集地点周围的磁倾角空间梯度而获得的实际测量值进行比较。 沿着南北轴和东西轴相对于我们的测试站点收集的动物的响应的比较也将被用来帮助区分“地图”和“非地图”的影响所造成的磁倾角的变化，并确定是否一个真正的双坐标地图被用来确定地理位置。 拟议中的实验将有助于更好地了解磁场的作用，在地图部分的归航。 这些实验也将有助于确定生物系统对地磁场变化的敏感性下限，并在更一般的水平上确定脊椎动物神经系统测量物理刺激绝对值的精度。

SummaryThe proposed research will investigate the ability of a vertebrate to use gradients in the inclination or 'dip angle' of the earth's magnetic field (defined as the angle between the magnetic field lines and gravity) to determine geographic ("map") position. Previous studies of homing orientation have shown that magnetic inclination may be used to derive one coordinate of a navigational map. To provide a more rigorous test of magnetic inclination's role in providing map information, the effects of small changes in magnetic inclination on homing orientation will be used to estimate characteristics of the local gradient of magnetic inclination within an animal's home range, e.g., the "home value" of inclination and the alignment of the gradient. These behaviorally derived estimates will then be compared with actual measured values obtained by mapping the spatial gradients of magnetic inclination around the sites where animals were collected. A comparison of the response of animals collected at sites along the north-south and east-west axes relative to our testing site will also be used to help distinguish "map" and "non-map" effects resulting from changes in magnetic inclination, and to determine whether a true bicoordinate map is being used to determine geographic position. The proposed experiments will contribute to a better understanding of the magnetic field's role in the map component of homing. These experiments will also help to determine the lower limits of the sensitivity of biological systems to variation in the geomagnetic field and, at a more general level, to determine the precision with which the vertebrate nervous system can measure the absolute values of physical stimuli.