Deutschlander et al. • AGE-DEPENDENT GEOMAGNETIC POSITIONING 
471 
Juveniles 
FIG. 1. Orientation of Australian Silvereyes in the natural geomagnetic field (C and D), the simulated North 
displacement magnetic field (SimN shown in A and B). and the simulated South displacement magnetic field (SimS shown 
in E and F); juveniles (A. C, E) and adults (B. D. F) are shown on the left and right, respectively. Small solid dots show 
individual nightly bearings for all birds tested in the specified condition and each line with a solid dot on the end represents 
the mean vector for an individual bird (as given in Table 2 by ot and r): all data are plotted with respect to magnetic north 
(mN = 0 ). The mean unimodal orientation of each group is shown graphically by the 95% confidence ellipse on each plot 
(Hotelling's one-sample test). The gray arrowheads outside each circle show the significant mean angular direction for each 
distribution. Dotted lines on the map show the geographic locations of the SimN average magnetic intensity, SimN average 
magnetic inclination, and SimS average magnetic inclination (SimS intensity is not on map): gray area shows the 
approximate winter range for Tasmanian-breeding Silvereyes. 
ilid not correspond (Fig. I) to any one geographic 
location due to the method used to change the 
magnetic Field (Fischer et al. 2003). The SimN 
values of intensity and inclination specify differ¬ 
ent magnetic ’latitudes' towards the equator with 
an inclination value on the Australian continent 
and an intensity value to the north of Australia. 
The SimS value of magnetic inclination corre¬ 
sponds to locations in southern Australia. How¬ 
ever. the SimS value of magnetic intensity does 
not exist at that region of the earth. 
Birds were tested for orientation after at least 
6 days of exposure to the experimental magnetic 
fields. A cube-surface coil similar to that used in 
the holding rooms generated the experimental 
magnetic fields in the testing room (Table J). 
Each bird was tested for 5-6 nights ( ‘displace¬ 
ment period"). Birds were returned to their 
holding cages between tests and w ere continually 
exposed to the SimN or SimS fields. The only 
time a bird was not exposed to the altered 
magnetic Held was during the 10-15 min transport 
