Testing avian compass calibration: comparative experiments with diurnal and nocturnal passerine migrants in South Sweden.

Susanne Åkesson,Christoffer Sjöholm,Alexandra Farkas,Gábor Horváth,Catharina Odin,Ramón Hegedüs,Mihaela Ilieva

doi:10.1242/bio.20149837

Abstract

ABSTRACTCue-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.

Highlights

Migratory songbirds are able to use geomagnetic information and celestial cues involving the position of the Sun and stars as well as the pattern of skylight polarization for orientation (e.g. Emlen, 1975; Able, 1980; Wiltschko and Wiltschko, 1995)
Muheim et al showed that migratory Savannah sparrows, Passerculus sandwichensis use the lowest part of the sky to recalibrate their magnetic compass (Muheim et al, 2006a; Muheim et al, 2008), while other studies by Wiltschko et al, Gaggini et al, Chernetsov et al and Schmaljohann et al have been unable to find the same response in other species of passerines tested in other geographical regions (i.e. Tasmanian Silvereyes, Zosterops l. lateralis in Australia, European robins, Erithacus rubecula in Germany, Pied flycatchers, Ficedula hypoleuca in Italy, Song thrushes, Turdus philomelos in Russia, Northern wheatears, Oenanthe oenanthe in Germany) (Wiltschko et al, 2008; Gaggini et al, 2010; Chernetsov et al, 2011; Schmaljohann et al, 2013)
Prior to the Muheim et al study (Muheim et al, 2006a), Sandberg et al performed cue-conflict experiments with a number of North American passerines in Alabama, resulting in interesting differences in orientation between cage and release experiments, and similarities between species in how the investigated species recalibrated their celestial compass based on geomagnetic information (Sandberg et al, 2000)

Summary

Introduction

Migratory songbirds are able to use geomagnetic information and celestial cues involving the position of the Sun and stars as well as the pattern of skylight polarization for orientation (e.g. Emlen, 1975; Able, 1980; Wiltschko and Wiltschko, 1995). Especially near the Polar Regions, migratory birds face a conflict between the directions given by the Sun and stellar compass compared to the magnetic compass, since geomagnetic declination exhibits large variations between nearby sites (Skiles, 1985). To cope with these difficulties, birds have been proposed to recalibrate their compasses both during ontogeny and adult life (Able and Able, 1990a; Able and Able, 1990b; Able and Able, 1993; Able and Able, 1995; Muheim et al, 2003). Results from cue-conflict experiments with caged birds have resulted in different outcomes and have repeatedly been reviewed by several authors discussing alternative explanations of the so far incoherent results (Able, 1993; Åkesson, 1994; Wiltschko et al, 1998; Wiltschko and Wiltschko, 1999; Muheim et al, 2006b)

Methods

Results

Conclusion