The Wilson Journal of Ornithology 124(3):467 -477, 2012 
AGE-DEPENDENT ORIENTATION TO MAGNETICALLY-SIMULATED 
GEOGRAPHIC DISPLACEMENTS IN MIGRATORY AUSTRALIAN 
SILVEREYES (ZOSTEROPS L. LATERALIS) 
MARK E. DEUTSCHLANDER. M JOHN B. PHILLIPS, 1 2 AND URSULA MUNRO 3 4 
ABSTRACT.—Geographic relocations of migratory passerines have shown that adults can compensate for physical 
displacements; juveniles on their first migration, however, use an innate clock-and-compass strategy and are unable to 
compensate for displacement. We examined the effects of changes in magnetic inclination and intensity on orientation of 
adult and juvenile Australian Silvcreyes i Zosit rops I lateralis) to learn if geomagnetic cues are used by a migratory 
passerine for geographic positioning. Silvcreyes, captured in breeding areas in Tasmania, were physically transported to a 
location along their migratory route and assessed tor orientation during autumn migration. Adults and juveniles exhibited 
seasonally appropriate, northeasterly orientation 1 1‘> and 23 east ol magnetic North, respectively) when tested under the 
natural geomagnetic field. Birds were then exposed to changes in the magnetic field that simulated either southern (SimS) 
or northern iSimN) locations near the beginning and end. respectively, ot their migratory route. Inexperienced juveniles 
continued to show seasonally appropriate orientation (3 and 358 . respectively) in both SimS and SimN magnetic fields. 
Adults, in contrast, exhibited changes in orientation but only when the experimental magnetic field w as consistent w ith a 
geographical displacement that should require compensatory orientation (i.e., SimN). Adults exposed to a SimS magnetic 
field continued to show season ally-appropriate orientation to the North (O'). However, adults exposed to magnetic fields 
simulating locations beyond their wintering areas (SimN) altered their orientation significantly, orienting bimodally and 
perpendicular (123 -303 ) to their seasonally appropriate migratory direction. These results are consistent with the 
presence of an age- or experience-dependent magnetic geographic position sense in migratory Australian Silvereyes. 
Received 20 February 2011. Accepted 4 March 2012. 
Juvenile migratory birds to accomplish their 
first migration have been shown to rely on a 
‘vector strategy' that combines an innate direc- 
(ional ‘compass’ heading with a temporal ‘clock’ 
program that affects migration distance (Helbig et 
al. 1989; Berthold 1990a, b; Helbig 1991 1996; 
Mouritsen 1998, 2001). However, age-dependent 
recoveries of geographically displaced migratory 
birds suggest adult passerines are able to use a 
different orientation strategy than juveniles; adult 
migratory birds can reorient to compensate for 
displacement in both North-South and East-West 
directions (e.g., Perdeck 1958; Mouritsen 2001, 
2003; Thorup et al. 2007: Chernetsov et al. 2008). 
These field experiments demonstrate adults can 
perceive their position, but they reveal little 
information about the cues used by birds to do so. 
Birds and many other organisms possess a 
magnetic compass sense to obtain directional 
information (reviewed in Wiltschko and Wiltschko 
1 Department of Biology. Hobart and William Smith 
Colleges. Geneva, NY 14456. USA. 
Department of Biological Sciences, Virginia Technical 
Institute and State University, Blacksburg. VA 24061. 
USA. 
Centre of Environmental Sustainability. School of (lie 
Environment, University of Technology, Sydney, P, 0. Box 
123. Broadway. NSW 2007. Australia. 
4 Corresponding author; e-mail; deutschlande@hws.edu 
1995). In addition, some animals may be able to 
sense gradients in the geomagnetic field to derive 
geographic-position information (reviewed in 
Freake et al. 2006), Specific values of the 
geomagnetic field can serve as an innate ‘sign 
post' or ‘releasing mechanism' for migrants to 
change their migratory behavior at appropriate 
locations, such as al stopover sites or migratory 
boundaries. For example, when exposed to grad¬ 
ually decreasing values of magnetic intensity and 
inclination, juvenile European Pied Flycatchers 
(FicednUi hypoleuca) shift their autumn orientation 
from southwest to southeast in magnetic fields that 
simulate those of southern Spain, as would freely 
migrating conspecifics. Southeast reorientation 
towards Africa prevents the birds from migrating 
over the Atlantic Ocean (Beck and Wiltschko 
1988). 
Use of the geomagnetic field as a ‘sign post' 
does not require that birds recognize their 
position; instead, specific geomagnetic field 
values elicit an appropriate ‘programmed’ change 
in the animal's behavior, orientation or otherwise, 
and can affect both adults and juveniles. For 
example, juvenile Thrush Nightingales ( Luscinia 
luscinia ) increase feeding rates in a magnetic Held 
simulating a stopover site in northern Egypt 
(Fransson et al. 2001. Kullberg cl al. 2003). True 
map-based navigation (Griffin 1952). in contrast. 
467 
