Sensory mechanisms of long-distance navigation in birds: a recent advance in the context of previous studies

Abstract

Displacement studies have clearly shown that experienced avian migrants are able to perform true navigation, i.e., they can find the correct direction leading to a target destination from unfamiliar sites. The sensory mechanisms of true navigation remain poorly understood, though some remarkable progress has been made in the last 10-15 years. There are two primary hypotheses explaining the sensory nature of navigation: (1) a magnetic map hypothesis proposes that birds use parameters of the geomagnetic field that are predictably distributed on the globe. As for the sensory nature of this hypothesis, it has been assumed by some researchers that the magnetic receptor cells reside in the upper beak (the so-called ''beak organ''), and transmit information via the trigeminal nerve to the brain; (2) an olfactory map hypothesis assumes that birds can smell their position by taking advantage of odours distributed in the atmosphere. There are a growing number of studies supporting both of the hypotheses mentioned though in different avian model species. In this review, an attempt is made to provide an overview of the evidence for different navigational cues proposed thus far, with the main focus on the recent studies addressing the magnetic and olfactory navigation hypotheses. Also, a list of key open questions, together with possible experimental approaches, is proposed.

Anosmic migrating songbirds demonstrate a compensatory response following long-distance translocation: a radio-tracking study

“…For true navigation, the ability of an animal to determine its current geographic position relative to the goal (a map sense) is crucial. However, the sensory systems and natural cues underlying the map sense for positioning remain poorly understood (Holland 2014; Kishkinev 2015). In this study, we focused on the role of the sense of smell (olfactory system) for longdistance navigation in a migratory songbird species-the Eurasian Reed Warbler (Acrocephalus scirpaceus; hereafter Reed Warblers).…”

Experienced migratory songbirds do not display goal-ward orientation after release following a cross-continental displacement: an automated telemetry study

“…This may be achieved by at least two methods. One way is for animals to detect their position on the globe using a bi-coordinate (or multi-coordinate) detection system in which individuals can detect variation in both latitude and longitude234. Alternatively, navigation can be achieved by an individual assessing its position relative to the goal or target without specific knowledge of geographical coordinates56.…”

How do migrating birds find their way?

“…(mosaic map hypothesis) 、 嗅 觉 激 活 假 说 (olfactory activation hypothesis)和梯度图假说(gradient map hypothesis). 镶嵌图假说认为, 鸟类可以通过识别风向中的 气味与巢位的关系, 达到准确导航(图1(a)) [6,20] . 嗅觉 激活假说认为, 嗅觉受体通过激活某种导航机制在 定向中发挥作用(图1(b)) [4,21] .…”

“…味浓度梯度, 不同气味的浓度差异与地理距离形成 坐标系, 被鸟类用于导航定向. 一旦特异性气味化合 物形成的梯度被识别, 鸟类就能通过释放地点气味 浓度确定所处的位置(图1(c, d)) [9,20,23,24] . [25] .…”

“…研究发现, 鸟类中存在将弱地磁强度放大的 机制, 该机制取决于FAD-TRP与FAD-维生素C光循 环以及FAD-TRP内自由基对的反应速率(图3) [35] . [4,20,21,23] . Three hypotheses about olfactory navigation [4,20,21,23] .…”