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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123, No. 1, March 2011 
of the feather for 8 I3 C and 5 I5 N analysis because 
the feathers were small, wrapping each in a 
separate tin capsule. There is a concern regarding 
isotopic variations within a feather (Wassenaar 
and Hobson 2006, Chang et al. 2008), and we did 
not attempt to examine different portions within a 
feather because it was necessary to use a large 
portion of the feather. 
Isotopic Analysis .—We analyzed 8 ,3 C and 8 I5 N 
of the feather samples using an elemental analyzer 
(Costech ECS 4010, Valencia, CA, USA) coupled 
to a Delta V mass spectrometer (Finnigan, Bre¬ 
men, Germany) at Brigham Young University. 
We used UCLA Carrera (a working standard from 
Ian Kaplan’s laboratory, UCLA, 8 13 C = 2.52%o) 
and LSVEC (NIST, 8 ,3 C = —46.5%o) as external 
standards for carbon, and USGS 25 (NIST, S ,5 N 
= -30.4%) and USGS 26 (NIST, 815N = 
53.5%o) as external standards for nitrogen. Instru¬ 
ment precision for the measurements was ±0.2%o 
for 8 13 C and 5 15 N. 
All stable isotope ratios of the samples are 
reported in per mil (%o) using the “delta” (5) 
analysis of variance (MANOVA) with Wilks' 
Lambda as the test statistic to identify feather 
isotopic differences among sites for each guild 
and each species. Bonferroni’s method was used 
to examine differences in isotope values between 
sites for post hoc tests of MANOVA. We used 
repeated-measure ANOVAs to examine year-to- 
year and within year fluctuations of feather 5 13 C 
and 8 I5 N values sampled from the same individ¬ 
uals. We only used 8 ,3 C and 8 ,5 N values of the 
first primary feather collected the first time the 
bird was captured in 2007 compared to 8 ,3 C and 
8 ,:> N values of an older primary feather collected 
from the same bird at the same time for year-to- 
year comparisons. We also examined the statisti¬ 
cal power of non-significant results of the year-to- 
year and within year repeated-measure ANOVAs. 
All statistical analysis were calculated with SAS 
statistical software (SAS 2003). 
notation. §sample [(Rsample/Rstandard) 1] X 
1,000, where the 5 sarnple is the isotope ratio of 
the sample relative to the standard, and R sam pie 
and R.standard are the fractions of heavy to light 
isotopes ( 13 C / ,2 C and l5 N/ 14 N) in the sample and 
standard, respectively. Delta values for carbon 
and nitrogen are expressed relative to PDB (Craig 
1957) and atmospheric nitrogen (Mariotti 1983), 
respectively. 
Data Analysis .—We limited our investigation 
of altitudinal trends and differences among sites 
for 8 ,3 C and S I5 N values to first primary feathers 
grown in 2007 collected from birds at time of first 
capture. The relationships between values of 5 I3 C, 
^' 5 N, and altitude for each guild and each species 
were analyzed using linear regression. Feather 
isotopic differences among sites for each guild 
and each species were measured using a one-way 
ANOVA tor data with normal distribution (tested 
by Shapiro-Wilk normality test) or a Kruskal- 
Wallis test if data were not normally distributed. 
Tukey’s post hoc tests were used to identify 
differences in isotope values between sites for 
data with normal distribution, and Bonferroni’s 
post hoc tests were used to identify differences in 
isotope values between sites for data without 
normal distribution. Combined analysis of multi¬ 
ple isotopes should increase the power of site 
identification (Webster et al. 2002). We used both 
eather 8 C and 5 15 N values in a multivariate 
RESULTS 
Altitudinal Pattern and Site Comparison of 
S ,5 N Values .—Feather 8 15 N values exhibited 
varying relationships to altitude among guilds 
and among species (Figs. 2-4). Insectivores were 
the only group which had a significant decrease in 
feather 8 I5 N values with increasing altitude 
(Fig. 4A). Feather 8 15 N values for other two 
guilds had no significant relationship to altitude 
(i.e., P > 0.05) (Figs. 2A and 3A). When 
analyzed by species, the Rufous-capped Babbler 
(Fig. 4D) was the only species which had 
significant decreases in feather 8 15 N values with 
increasing altitude. White-browed Bush Robins, 
however, had a significant increase in feather 8 15 N 
values with increasing altitude (Fig. 4E). The R 2 
of Rufous-capped Babblers and White-browed 
Bush Robins were 0.27 and 0.37, respectively. 
Feather S I5 N values for the other seven species 
had no significant relationship to altitude (i.e., P 
> 0.05) (Figs. 2B, C; 3B, C, D; 4B, C). 
Feather 8 I5 N values were significantly different 
between some, but not all, sites for omnivores 
(Fig. 3A) and insectivores (Fig. 4A). Herbivores 
did not have significant differences across sites 
(Fig. 2A). When analyzed by species, feather 8 15 N 
values were significantly different between some, 
but not all, sites for Grey-cheeked Fulvettas 
(Fig. 3B), Grey-hooded Fulvettas (Fig. 3D), Ru¬ 
fous-capped Babblers (Fig. 4D), and White- 
browed Bush Robins (Fig. 4E). The other five 
species did not have significant differences across 
sites (Figs. 2B, C; 3C; 4B, C). 
