Geomagnetic Position Fixing

拟议的研究将调查脊椎动物利用地球磁场的倾斜度或“倾角”（定义为磁力线与重力之间的角度）来确定地理位置（“地图”）的能力。以前对寻的方向的研究表明，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方面的作用进行更严格的测试，将使用磁倾角的微小变化对归巢方向的影响来估计动物家园范围内局部磁倾角梯度的特征，例如，倾角的“家园值”和梯度的对齐。然后将这些行为推断的估计值与实际测量值进行比较，这些测量值是通过绘制收集动物的地点周围的磁倾斜度的空间梯度而获得的。对比在南北轴线和东西轴线上相对于我们的测试地点收集的动物的反应，也将有助于区分由磁倾斜变化引起的“地图”和“非地图”效应，并确定是否使用了真正的双坐标地图来确定地理位置。提出的实验将有助于更好地理解磁场在归巢的地图成分中的作用。这些实验还将有助于确定生物系统对地磁场变化的敏感度下限，并在更一般的层面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.