title: Testing avian compass calibration: comparative experiments with diurnal and nocturnal passerine migrants in South Sweden.
abstract: Cue-conflict experiments were performed to study the compass calibration of one predominantly diurnal migrant, the dunnock (Prunella modularis), and two species of nocturnal passerine migrants, the sedge warbler (Acrocephalus schoenobaenus), and the European robin (Erithacus rubecula) during autumn migration in South Sweden. The birds' orientation was recorded in circular cages under natural clear and simulated overcast skies in the local geomagnetic field, and thereafter the birds were exposed to a cue-conflict situation where the horizontal component of the magnetic field (mN) was shifted +90° or -90° at two occasions, one session starting shortly after sunrise and the other ca. 90 min before sunset and lasting for 60 min. The patterns of the degree and angle of skylight polarization were measured by full-sky imaging polarimetry during the cue-conflict exposures and orientation tests. All species showed orientation both under clear and overcast skies that correlated with the expected migratory orientation towards southwest to south. For the European robin the orientation under clear skies was significantly different from that recorded under overcast skies, showing a tendency that the orientation under clear skies was influenced by the position of the Sun at sunset resulting in more westerly orientation. This sun attraction was not observed for the sedge warbler and the dunnock, both orientating south. All species showed similar orientation after the cue-conflict as compared to the preferred orientation recorded before the cue-conflict, with the clearest results in the European robin and thus, the results did not support recalibration of the celestial nor the magnetic compasses as a result of the cue-conflict exposure.
authors.affiliation: Department of Biology, Centre for Animal Movement Research, Lund University, Ecology Building, SE-223 62 Lund, Sweden Susanne.Akesson@biol.lu.se.
authors.forename: Susanne
authors.initials: S
authors.lastname: Åkesson
authors.affiliation: Department of Biology, Centre for Animal Movement Research, Lund University, Ecology Building, SE-223 62 Lund, Sweden.
authors.forename: Catharina
authors.initials: C
authors.lastname: Odin
authors.affiliation: Max Planck Institute for Informatics, Campus E1.4, D-66123 Saarbrücken, Germany Environmental Optics Laboratory, Department of Biological Physics, Physical Institute, Eötvös University, H-1117 Budapest, Pázmány sétány 1, Hungary Manao Group, INRIA Sud-Ouest Bordeaux, 33400 Talence Cedex, France.
authors.forename: Ramón
authors.initials: R
authors.lastname: Hegedüs
authors.affiliation: Department of Biology, Centre for Animal Movement Research, Lund University, Ecology Building, SE-223 62 Lund, Sweden Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria.
authors.forename: Mihaela
authors.initials: M
authors.lastname: Ilieva
authors.affiliation: Department of Biology, Centre for Animal Movement Research, Lund University, Ecology Building, SE-223 62 Lund, Sweden.
authors.forename: Christoffer
authors.initials: C
authors.lastname: Sjöholm
authors.affiliation: Environmental Optics Laboratory, Department of Biological Physics, Physical Institute, Eötvös University, H-1117 Budapest, Pázmány sétány 1, Hungary.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Farkas
authors.affiliation: Environmental Optics Laboratory, Department of Biological Physics, Physical Institute, Eötvös University, H-1117 Budapest, Pázmány sétány 1, Hungary.
authors.forename: Gábor
authors.initials: G
authors.lastname: Horváth
keywords: Acrocephalus schoenobaenus; Erithacus rubecula; Prunella modularis; compass calibration; magnetic compass; migratory birds; orientation; passerines