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，许多策略已经进化到允许动物返回到已知的目标。研究空间导航揭示了大脑的结构和功能，以及它如何受到年龄，损伤和疾病的影响。它还揭示了许多关于感觉系统如何整合以提供在环境中定位位置的信息。其中最引人注目的航海家是小型迁徙鸣禽。这些动物在繁殖地和冬季地点之间旅行数千公里，并表现出非凡的精确性，能够年复一年地返回同一个繁殖地，有时甚至筑巢。这些小型鸟类也表现出非凡的灵活性，能够纠正从正常迁徙路线的大位移，到他们以前不可能到达的地方，并返回他们正常的繁殖或冬季地区。这似乎是在它们第一次从出生地到第一次迁徙后到达的冬季土地的迁徙旅程中学会的。科学家们推测，它们是用类似于地图和指南针的东西来导航的。这一过程的地图步骤是至关重要的，因为它使他们能够确定与他们所期望的目标相关的位置，并且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。这是一种似乎超越人类的能力，而不诉诸技术，然而鸟类可以根据环境中感知到的线索做到这一点。虽然许多研究工作已经花费在试图发现他们如何实现这一点，它仍然基本上没有解决，因为我们不完全了解什么环境线索是用来确定他们的位置。公认的智慧是，地图中使用的线索和感觉与指南针中使用的线索和感觉是分开的。因此，天体线索，如太阳和恒星提供指南针方向，但不是位置。唯一的例外是地球的磁场。然而，有人认为鸟类需要并拥有两个独立的磁感觉系统，一个是位于眼睛中的罗盘步骤，另一个是位于喙中的地图步骤。然而，最近的证据对是否存在基于喙的感觉提出了质疑。除此之外，新的证据表明，用于定位鸟类位置的一个线索是decastrine，在世界上的一些地方，decastrine从东到西都不同，即它提供了经度的线索。这是通过将磁罗盘检测到的磁北与天体罗盘（太阳或星星）检测到的地理（真）北进行比较来计算的。这意味着与先前的预期相反，地图中使用的感觉系统并不是与指南针分开的，而是可能被整合到指南针中。鸟类究竟是如何计算昼夜节律的？由于大多数鸟类都是夜间迁徙的，因此星星罗盘是主要的候选者，但一些研究表明，这些鸟类用日落校准磁罗盘，而不是星星。鸟类需要两种磁性感官吗？如果鸟类可以用眼睛的磁感应来计算它们的经度位置，那么它们是否也可以用这种感觉系统来计算它们的纬度位置呢？长期以来被认为是指南针的天体线索，实际上在地图中发挥了更大的作用，因为它们也可以提供纬度信息。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精确方式仍然是完全未知的。该研究项目将使用一种小型鸣禽--欧亚苇莺来调查这些问题，以提供新的见解，了解它如何能够在欧洲的繁殖地和撒哈拉以南非洲的冬季场地之间航行。

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.