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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 124, No. 3. September 2012 
TABLE I. Home-range size of female Dark-eyed Juncos and metrics of tracking effort and female characteristics. 
Mountain Lake Biological Station. Pembroke, Virginia. USA. The effect of implant type was tested using a Kruskal-Wallis 
test (x ; ). All other relationships were tested using a Spearman's Rho Correlation (r). 
Home-range size thal 
No. of locations 
Tracking time (hrs) 
Julian date 
Age 
Nesting attempt 
Implant 
0.156 
53 
8.17 
202 
2 
4 
Control 
0.350 
65 
10.00 
149 
1 
1 
Control 
0.390 
62 
9.84 
197 
1 
3 
Control 
0.613 
65 
10.00 
188 
1 
3 
Testosterone 
0.657 
59 
9.00 
150 
1 
1 
Testosterone 
1.215 
65 
10.00 
175 
4 
2 
Control 
2.450 
65 
10.00 
189 
1 
1 
None 
r or ■/; 
0.493 
0.493 
-0.214 
-0.045 
-0.543 
2.89 
P 
0.261 
0.261 
0.645 
0.924 
0.208 
0.235 
females receiving transmitters had a brood size of 
three. 
We used a TRX 1000-S receiver with a three- 
element Yagi antenna (Wildlife Materials Inc.. 
Carbondale. IL, USA) to track each female via 
homing tor 10 hrs, 2 hrs on the afternoon of day 3 
of nestling life (1300-1800 hrs EST) and 2 hrs on 
the morning (0800-1200 hrs EST) and afternoon 
(1300-1800 hrs EST) of days 4 and 5 of nestling 
life. We did not track during periods of heavy rain 
and collected <10 hrs of data for three females 
(mean = 9.56 hrs, range = 8.17-10.0 hrs). Trans¬ 
mitters were removed on the morning of day 6 of 
nestling lite, We chose to track during the early-to- 
mid nestling period (nestling juncos typically 
fledge at 11—12 days post-hatch) as opposed to 
the mid-to-late nestling period in an effort to 
maximize our sample as nests are frequently 
depredated even after reaching the nestling stage. 
We only sampled females for 3 days to limit the 
amount of time that each female carried the 
transmitter and to ensure the transmitters could 
be removed without Hedging the nestlings early. 
DGR recorded female location and behavior 
every 10 min for the duration of tracking. We 
marked location points with flagging tape after the 
female had moved at least 15 m distant to avoid 
affecting the female’s movements. The 10-min 
interval between observation points was chosen 
to ensure our total number of observation points 
(n = 65) per female was similar to the mean 
number ol points per female reported by Neudorf 
et al. (2002; 71.5 points/female) to facilitate a 
meaningful comparison of home-range size be¬ 
tween our studies. 
Six of the seven females received a subcutane¬ 
ous implant on the left flank, consisting of a 7-mm 
(1.47 mm internal diam, 1.96 mm outside diam) 
Silastic® tube (Dow Corning Corp.. Midland. MI, 
USA) filled with 5 mm (~ 0.1 mg) of crystalline 
testosterone (Sigma-Aldrich Inc., St. Louis. MO, 
USA) or an empty tube filled with air as part of a 
separate study investigating the impact of elevated 
plasma testosterone on female reproductive be¬ 
havior (O'Neal et al. 2008). Implants were in¬ 
serted at least 2 weeks prior to attachment of a 
transmitter to allow females to recover and adjust 
physiologically to the implant. Female juncos 
receiving implants in this study and previous 
stuilies had full mobility immediately alter 
implantation and remained active breeders for 
the duration of the breeding season, suggesting the 
implantation process had limited effects on the 
activity of our subjects (Clotfelter et al. 2004. 
O’Neal et al. 2008). Previous studies of the effect 
of elevated testosterone on male spatial activity 
successfully implanted males with larger testos¬ 
terone implants than those used in our study and 
attached transmitters of a similar size without any 
noticeable adverse effects on male body mass, 
activity, or survival (Chandler et al. 1994. 1997: 
Smulders cl al. 2000). All methods used were 
reviewed and approved by the Indiana University. 
Bloomington. Institutional Animal Care and Use 
Committee (BIACUC Protocol # 06-242) prior to 
data collection. 
Estimating Home-range Size .—We attempted to 
obtain 65 observation points for each female 
(Table I), which were translated into coordinates 
using a Trimble Pathfinder Pro XRS Global 
Positioning System (GPS) unit (Trimble Naviga¬ 
tion Limited, Sunnyvale. CA, USA) with an 
accuracy of <1 m. GPS positions were differen¬ 
tially corrected using GPS Pathfinder Office 2.90 
( Trimble Navigation Limited. Sunnyvale. CA. 
USA) with correction data from the Blacksburg. 
