TY - JOUR

T1 - A magnet attached to the forehead disrupts magnetic compass orientation in a migratory songbird

AU - Packmor, Florian

AU - Kishkinev, Dmitry

AU - Bittermann, Flora

AU - Kofler, Barbara

AU - Machowetz, Clara

AU - Zechmeister, Thomas

AU - Zawadzki, Lucinda

AU - Guilford, Tim

AU - Holland, Richard

N1 - © 2021. Published by The Company of Biologists Ltd.

PY - 2021/11

Y1 - 2021/11

N2 - ABSTRACT For studies on magnetic compass orientation and navigation performance in small bird species, controlled experiments with orientation cages inside an electromagnetic coil system are the most prominent methodological paradigm. These are, however, not applicable when studying larger bird species and/or orientation behaviour during free flight. For this, researchers have followed a very different approach, attaching small magnets to birds, with the intention of depriving them of access to meaningful magnetic information. Unfortunately, results from studies using this approach appear rather inconsistent. As these are based on experiments with birds under free-flight conditions, which usually do not allow exclusion of other potential orientation cues, an assessment of the overall efficacy of this approach is difficult to conduct. Here, we directly tested the efficacy of small magnets for temporarily disrupting magnetic compass orientation in small migratory songbirds using orientation cages under controlled experimental conditions. We found that birds which have access to the Earth's magnetic field as their sole orientation cue show a general orientation towards their seasonally appropriate migratory direction. When carrying magnets on their forehead under these conditions, the same birds become disoriented. However, under changed conditions that allow birds access to other (i.e. celestial) orientation cues, any disruptive effect of the magnets they carry appears obscured. Our results provide clear evidence for the efficacy of the magnet approach for temporarily disrupting magnetic compass orientation in birds, but also reveal its limitations for application in experiments under free-flight conditions.

AB - ABSTRACT For studies on magnetic compass orientation and navigation performance in small bird species, controlled experiments with orientation cages inside an electromagnetic coil system are the most prominent methodological paradigm. These are, however, not applicable when studying larger bird species and/or orientation behaviour during free flight. For this, researchers have followed a very different approach, attaching small magnets to birds, with the intention of depriving them of access to meaningful magnetic information. Unfortunately, results from studies using this approach appear rather inconsistent. As these are based on experiments with birds under free-flight conditions, which usually do not allow exclusion of other potential orientation cues, an assessment of the overall efficacy of this approach is difficult to conduct. Here, we directly tested the efficacy of small magnets for temporarily disrupting magnetic compass orientation in small migratory songbirds using orientation cages under controlled experimental conditions. We found that birds which have access to the Earth's magnetic field as their sole orientation cue show a general orientation towards their seasonally appropriate migratory direction. When carrying magnets on their forehead under these conditions, the same birds become disoriented. However, under changed conditions that allow birds access to other (i.e. celestial) orientation cues, any disruptive effect of the magnets they carry appears obscured. Our results provide clear evidence for the efficacy of the magnet approach for temporarily disrupting magnetic compass orientation in birds, but also reveal its limitations for application in experiments under free-flight conditions.

KW - Celestial compass

KW - Eurasian Reed Warbler

KW - Environmental cue

KW - Orientation cage

KW - Navigation

KW - Migration

KW - Orientation

KW - Songbird

KW - star compass

U2 - 10.1242/jeb.243337

DO - 10.1242/jeb.243337

M3 - Article

C2 - 34713887

VL - 224

JO - Journal of Experimental Biology

JF - Journal of Experimental Biology

SN - 0022-0949

IS - 22

M1 - 243337

ER -