Unravelling the map and compass in bird navigation

在太空中定向和导航的能力对所有动物来说都是一种至关重要的适应能力，许多策略已经发展出来，让动物能够回到已知的目标。研究空间导航揭示了大脑的结构和功能，以及它是如何受到年龄、损伤和疾病的影响的。它还揭示了感官系统是如何整合在一起，为在环境中定位位置提供信息的。其中最引人注目的是小型候鸟。这些动物在繁殖区和冬季地点之间旅行数千公里，表现出惊人的精确度，能够年复一年地返回相同的繁殖地，有时甚至筑巢。这些小鸟也表现出了非凡的灵活性，能够纠正它们正常迁徙路线上的大移位，到它们以前不可能去过的地方，然后回到它们正常繁殖或过冬的地方。这似乎是在它们从它们出生的繁殖区到第一次迁徙后到达的冬季土地的第一次迁徙过程中学会的。科学家假设他们使用类似地图和指南针的东西以这种方式导航。这个过程的地图步骤是至关重要的，因为它允许他们根据他们想要的目标来确定他们的位置，并被认为基本上像我们的笛卡尔坐标系一样，提供纬度和经度信息。这是一种人类在不借助科技的情况下似乎无法实现的能力，但鸟类可以根据环境中感知的线索做到这一点。虽然已经花费了大量的研究努力来试图发现它们是如何做到这一点的，但它基本上仍然没有得到解决，因为我们还不完全了解什么环境线索被用来确定它们的位置。普遍的看法是，地图中使用的线索和感官与指南针中使用的线索和感官是分开的。因此，太阳和恒星等天体信号提供的是指南针方向，而不是位置。例外的是地球的磁场。然而，有观点认为，鸟类需要并拥有两个独立的磁性感官系统，一个是位于眼睛的罗盘步，另一个是位于喙的地图步。然而，最近的证据对基于喙的感觉是否存在提出了质疑。除此之外，新的证据表明，用来定位鸟类位置的一种线索是赤纬，在世界上一些地区，它从东到西有所不同，即它提供了经度的线索？这是通过比较磁罗盘探测到的磁北和天文罗盘(太阳或恒星)探测到的地理(真)北来计算的。这意味着，与之前的预期相反，地图中使用的感觉系统并不是与指南针分开的，而是可能集成在其中。然而，这一发现留下了许多悬而未决的问题。鸟类究竟是如何计算赤纬的？由于大多数鸟类是夜间迁徙的，所以星罗盘是主要的候选者是有道理的，但一些研究表明，这些鸟是根据日落而不是恒星来校准磁罗盘的。鸟类需要两种磁感吗？如果鸟类可以用眼睛的磁感来计算它们的经向位置，它们是否也能用这个感官系统来计算它们的纬度位置？长期以来一直被归类为指南针角色的天体信号，实际上在地图上发挥着更大的作用，因为它们也可以提供关于纬度的信息。鸟类是如何学习这些线索的？鸟类必须在它们的第一次迁徙旅程中学习这些线索，但它们构建这张地图的确切方式仍然完全未知。这项研究项目将使用一种小型鸣鸟欧亚芦莺来研究这些问题，为它如何在欧洲的繁殖地和撒哈拉以南非洲的冬季栖息地之间航行提供新的见解。

The ability to orient and navigate in space is a vital adaptation for all animals and many strategies have evolved to allow animals to return to a known goal. Studying spatial navigation has revealed much about the structure and function of the brain, how it is impacted by age, damage and disease. It has also revealed much about how sensory systems are integrated to provide information for locating position within the environment. Among the most remarkable navigators are small migratory songbirds. These animals travel thousands of kilometres between breeding areas and winter sites, and show remarkable precision, being able to return to the same breeding site, sometimes even nest, year after year. These small birds also show remarkable flexibility, being able to correct for large displacements from their normal migratory path, to places they could not have been to before, and return to their normal breeding or winter area. This appears to be learned during their first migratory journey from the breeding area they were born in, to the winter ground that they reach after their first migration. Scientists hypothesise that they navigate in this way using something akin to a map and a compass. The map step of this process is crucial, as it allows them to determine their location in relation to their desired goal and is thought to function essentially like our Cartesian coordinate system, providing latitude and longitudinal information. This is an ability that seems to be beyond humans without resorting to technology, and yet birds can do this based on cues sensed in the environment. Whilst much research effort has been expended in trying to discover how they achieve this, it remains essentially unsolved, as we do not fully understand what environmental cues are used to determine their position. Received wisdom has it that the cues and senses used in the map are separate from those used in the compass. Thus celestial cues such as the sun and stars provide compass directions, but not location. The exception to this is the Earth's magnetic field. However, It has been argued that birds require and possess two separate magnetic sensory systems, one for the compass step, located in the eye, and a second for the map step, located in the beak. However, recent evidence has called into question whether the beak based sense exists. In addition to this, new evidence indicates that one cues that is used in locating the birds' position is declination, which varies from east to west in some parts of the world, i.e. It provides a cue to longitude?. This is calculated by comparing magnetic north detected by the magnetic compass with geographic (true) north detected by a celestial compass (the sun or stars). This means that contrary to previous expectations, the sensory systems used in the map are not separate from the compass, but may be integrated into it. This discovery leaves many open questions however. How exactly to birds calculate declination? As the majority of birds are night migrants it makes sense that the star compass is the primary candidate, but some studies suggest that these birds calibrate the magnetic compass with sunset, not the stars. Do birds need two magnetic senses? If birds can calculate their longitudinal position with the magnetic sense in the eye, do they also calculate their latitudinal position with this sensory system? Do celestial cues, long relegated to the role of compass, actually play a greater role in the map, as they also could provide information on latitude. How do birds learn these cues? Birds must learn these cues on their first migratory journey, but the precise way in which they build this map is still entirely unknown. This research project will investigate these questions using a small songbird, the Eurasian reed warbler, to provide new insights into how it is able to navigate between its breeding grounds in Europe and winter grounds in Sub Saharan Africa.