Mechanisms of Body Alignment in a Diurnal Songbird Migrant

ABSTRACT Animals align their body in relation to different environmental cues, including spontaneous directional responses relative to the geomagnetic field known as magnetic body alignment. The biological significance of this behavior, however, remains undetermined for most taxa. In previous studies, migratory songbirds aligned their body with the cardinal directions of the geomagnetic field and their migratory direction at different times of day. To explore the mechanisms of the alignment behavior in songbirds, we studied a diurnal migrant, the dunnock ( Prunella modularis ) in captivity. We captured juvenile dunnocks at stopover sites during autumn migration and assigned them to three experiments performed under controlled photic and magnetic conditions in cylindrical cages, each fitted with a circular perch enabling birds to select resting positions freely. We repeatedly measured the alignment of individual birds as the directional body orientation during rest, before and after a prolonged period of rest at sunset and sunrise on each experimental night. Several alternative orientation cues were considered to investigate the alignment of the population. Our results revealed that individuals performed angular body alignment with high consistency; however, a preferred direction was not expressed on a population level. Furthermore, the alignment position of each individual was retained throughout the resting period. These findings support the prediction that body alignment is individually selected and may be involved in compass calibration.