Abstract
Spontaneous magnetic alignment is the simplest known directional response to the geomagnetic field that animals perform. Magnetic alignment is not a goal directed response and its relevance in the context of orientation and navigation has received little attention. Migratory songbirds, long-standing model organisms for studying magnetosensation, have recently been reported to align their body with the geomagnetic field. To explore whether the magnetic alignment behaviour in songbirds is involved in the underlying mechanism for compass calibration, which have been suggested to occur near to sunset, we studied juvenile Eurasian reed warblers (Acrocephalus scirpaceus) captured at stopover during their first autumn migration. We kept one group of birds in local daylight conditions and an experimental group under a 2 h delayed sunset. We used an ad hoc machine learning algorithm to track the birds’ body alignment over a 2-week period. Our results show that magnetic body alignment occurs prior to sunset, but shifts to a more northeast–southwest alignment afterwards. Our findings support the hypothesis that body alignment could be associated with how directional celestial and magnetic cues are integrated in the compass of migratory birds.
Highlights
The geomagnetic field has been shown to be a reliable source for orientation and navigation in many animals (Wiltschko and Wiltschko 1995; Lohmann et al 2007; Mouritsen 2018)
We provide the first experimental evidence that magnetic body alignment with cardinal magnetic directions occurs in a nocturnal migratory songbird at sunset, and that such behaviour could be extended in response to an artificially delayed sunset
Different studies have tried to explain how each compass mechanism can translate into a migratory route, but so far, there is no conclusive answer on which compass mechanism is used during migration (Alerstam et al 2001; Åkesson and Bianco 2016, 2017)
Summary
The geomagnetic field has been shown to be a reliable source for orientation and navigation in many animals (Wiltschko and Wiltschko 1995; Lohmann et al 2007; Mouritsen 2018). The adaptive significance of magnetic body alignment in animals still. Magnetosensation is a challenging phenomenon to study and the magnetic sensory mechanism is still not completely understood (Phillips et al 2010; Mouritsen 2018). Magnetic body alignment is difficult to study, because it can be affected by other environmental cues such as wind, slopes, landmarks, celestial bodies, olfactory signals, etc., which have extensively been discussed (Begall et al 2013; Burda et al 2020). Due to the typical bimodal orientation response, particular care should be implemented in handling body alignment data (Begall et al 2013) and in monitoring the geomagnetic field during data acquisition (Hart et al 2013a; Bianco et al 2019a, b).
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