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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 124. No. 3. September 2012 
changes in iheir mean vector length (Wilcoxon 
Rank Sum test. W = 33. P = 0.14 for both 
comparisons). 
Adult Orientation During Exposure to SitnN 
and SitnS Magnetic Fields. —SimS adults contin¬ 
ued to orient towards the north with a mean bearing 
of 0° (r = 12.7. P < 0.05; Fig. 1F). The distribution 
of adults exposed to the SimN magnetic Held was 
not significantly oriented to the north or in any other 
uni modal direction if = 2.6. P > 0.05; Fig IB). 
SimN adults were bimodally oriented along a mean 
axis of 123 -303 (/’ =- 30.2. P < 0.05, on doubled 
angles), roughly perpendicular to their seasonally 
appropriate migratory direction to the NNE exhib¬ 
ited in control tests. Adults exposed to the SimN 
magnetic field deviated more from their control 
direction than SimS adults (W = 70.5, P = 0.013); 
SimN adults also had shorter mean vector lengths 
compared to SimS adults (W = 64, P — 0.035). 
Nightly Activity and Concentration of Orienta¬ 
tion. —Median activity and median concentration 
were not normally distributed and were trans¬ 
formed using the lOgwi of activity and the square 
root of concentration, respectively. Both variables 
fit the requirements after transformation for 
ANOVA (Kolmogorov-Smirnov Test after trans¬ 
formation; activity; Z = 0.65 and 0.53 with P- 
values of 0.79 and 0.95, respectively, for the 
control and displacement periods; concentration: 
Z = 0.70 and 0.50 with F-values of 0.72 and 
0.97). 
A significant three-way interaction was ob¬ 
served for median nightly activity among time 
(the within-subjects factor that reflects the com¬ 
parison between the control and displacement 
periods), age. and type of displacement (Repeated 
measures ANOVA. interaction: F UN — 4.435. P = 
0.044; Fig. 2), All four groups during the control 
period had similar activity levels. Each group's 
activity decreased during the simulated displace¬ 
ment (time: F lJ9 = 16.64. P = 0.0003; Fig. 2). 
However, juveniles in the SimN displacement 
exhibited a greater decrease in activity than any 
ol the other three groups, which is reflected by the 
significant statistical interaction among time, age. 
and type of displacement. 
Each group of birds exhibited an increase in 
median nightly concentration between the control 
and the displacement periods (Repeated measures 
ANOVA. time: F tM = 4.973, P = 0.034; Fig. 2). 
There was a weak between-subjects effect of 
displacement independent of time (F U2y = 4.165. 
P - 0.05). Birds assigned to the SimS group. 
regardless of age and whether the tests were 
during the control or simulated displacement 
periods, had higher concentration values (or were 
less dispersed in individual nightly orientation) 
than birds in the SimN group. 
DISCUSSION 
Only adult Silvereyes exposed to the SimN 
magnetic field altered their orientation; SimN 
adults exhibited axial (or bimodal) orientation 
along a WNW-ESE axis roughly perpendicular to 
their seasonally appropriate NNE direction. How¬ 
ever, adults exposed to the SimS magnetic field, 
and juveniles exposed to both the SimN and SimS 
fields, continued to show seasonally appropriate 
northward orientation that was indistinguishable 
from the orientation exhibited during control tests. 
Thus, changes in magnetic intensity and incliiw- 
lion affected orientation (1) only in adults, which 
have previous migratory experience, and (2) only 
when the magnetic field change was consistent 
with geographical location(s) that were beyond 
the goal, in this case, iheir wintering area. 
The change in orientation of SimN adults was 
not accompanied by a specific change in either 
activity or in the concentration of nightly activity, 
indicating the ‘motivation’ of the SimN adults to 
orient (i.c., migratory restlessness) did not differ 
from the other three groups. All birds, regardless 
of age or simulated displacement, had a decrease 
in nightly activity during the displacement period; 
this would be expected as migratory restlessness 
diminishes towards the end of migration or as the 
birds become acclimated to repeated testing. 
ANOVA indicated a weak interaction between 
test condition and age for activity, reflecting that 
SimN juveniles exhibited a greater decrease in 
activity compared to the other three groups; this 
change in activity was not associated with a 
change in the orientation of SimN juveniles. The 
decrease in activity was least pronounced in SimN 
adults (Fig. 2). the only group that exhibited a 
significant change in orientation when exposed 
to the simulated displacement. The nightly con¬ 
centration of orientation increased ti.e.. less dis¬ 
persion around the individuals' mean nightly 
direction) in all four groups during the displace¬ 
ment period. This might suggest all birds became 
better oriented, but an increase in concentration 
could be the result of a decrease in the nightly 
activity of birds. 
We included hatch-year juveniles with no 
migration experience; juveniles possess a magnetic 
