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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 124. No. 3. September 2012 
between the holding and testing rooms. Only 
about half of the birds in each treatment group 
could be tested on a given night, and birds from 
the two groups were tested alternately on 
successive nights: thus individual birds were 
tested once every four nights. 
Median activity, median concentration, and 
mean vector were calculated lor each bird from 
its nightly bearings (as in the control period) to 
examine the orientation ol birds exposed to the two 
experimental treatments (Table 2). Three birds that 
were inactive (<35 scratches) for four or more 
nights during the displacement period were not 
used for statistical comparisons (Table 2). as 
reliable mean vectors could not be calculated from 
fewer than three nights of activity. 
Magnetic Field Measurements and Manipula¬ 
tions.—Magnetic fields were measured using a 
Cesium magnetometer (Model #757010. Seintrex 
Ltd.. Concord. ON. Canada) operated with a TM4 
interface (Geophysical Technology Ltd.. University 
of New England. Armidale. Australia). Changes 
in the geomagnetic ITdd were accomplished by 
altering only the vertical component of the magnetic- 
field. which simultaneously changed both total 
intensity and inclination (Fischer et al. 2003). 
Altering the vertical component of the magnetic 
field did not change the horizontal alignment or 
declination of the magnetic field. 
A 2-irr. four-element. Merritt's cube-surface 
coil (Kirschvink 1992) was oriented vertically in 
each holding room to either add to or subtract 
from the vertical component of the geomagnetic 
field for SimS or SimN' conditions, respectively. 
Each coil was powered by one channel of a 
current-regulated two-channel power supply. A 
vertically aligned. 2.1-nr. four-element. Merrilfs 
cube-surface coil was used to alter the magnetic 
field in the testing room. A two-channel power 
supply (one channel for SimS and one for SimN) 
was used to provide current to the coil. Current 
was applied to both coils to match the magnetic 
fields during testing as closely as possible to the 
holding fields (Table 1). 
Statistical Analyses .—We ascertained the over¬ 
all orientation ot each group of birds (each age 
class for each simulated displacement), using one- 
sample Hotelling's test, which considers both 
bearing and length of each bird’s mean vector 
(Batschelet 1981). The I fotelIing's test generates a 
95% confidence ellipse for the mean orientation 
ol any significantly oriented sample (Fig. I). We 
also examined the change in mean angular 
direction between the control and displacement 
tests (A direction = displacement mean bearing 
minus control mean bearing for each bird) and the 
change in mean vector length (A length = 
displacement vector length minus control vector 
length for each bird) to evaluate the effect of 
simulated displacement on individual orientation. 
We compared the changes in direction and in 
vector length between different treatment groups 
with noil-parametric Wileoxon Rank Sum tests on 
each set of independent variables. 
Median nightly activity and median concentra- 
lion were measured before and during simulated 
displacement for each individual (Table 2). These 
median values for activity and concentration were 
used in two repeated measures ANOVAs (using 
the GLM procedure of SPSS 11.0. 2001) to 
ascertain if birds changed migratory behavior 
between the control and displacement periods (the 
‘within-subjeets’ factor, which we designated as 
'time') and to learn whether activity or concen¬ 
tration varied as a function of age or type ol 
displacement (the 2 'between-subjects' factors). 
The distribution of median values for activity and 
concentration was tested for normality using a 
one-sample Kolmogorov-Smirnov test. Data were 
transformed where appropriate to conform to 
requirements of parametric analysis. Data were 
back-transformed for presentation (Fig. 2). All P 
values are two-tailed. 
RESULTS 
Control Orientation. —Juvenile and adult Silver- 
eyes in the ambient magnetic field of Armidale 
oriented towards the north-northeast (NNE) with 
mean hearings of 23 and 19 . respectively (one- 
sample Hotelling’s test, r = 66.3 and 131.2. P ' 
0.005 for both samples). Thus, both age groups of 
birds exhibited seasonally appropriate orientation in 
the local geomagnetic field (Table 2: Fig. 1C. D). 
Juvenile Orientation During Exposure to SimS 
and SimS Magnetic Fields. —Juveniles in both 
SimN (Fig. 1 Aland SimS displacements (Fig. IE) 
were well oriented with mean bearings of 358 and 
3 (r = 57.4 and 85.5, P < 0.005 for both sam¬ 
ples). Most juveniles in both experimental mag¬ 
netic fields oriented slightly counterclockwise ol 
their control directions with a slight increase in 
mean vector length (Table 2). However, neither 
treatment resulted in a significant difference in 
orientation from that exhibited during the control 
period: the two groups of juveniles did not differ in 
their deviations from their control direction or in 
