Chang et al. • ALTITUDINAL CHANGES 
OF 5 15 N AND 5 13 C IN MONTANE BIRDS 45 
within-year for most of the species examined. 
This suggests these birds feed on similar diets and 
at similar feeding locations/altitudes when molt¬ 
ing flight feathers both within a single season and 
from year to year. Also, these birds may exhibit 
strong feeding site fidelity during molt periods. 
However, the scale of what constitutes a feeding 
site as indicated by isotopic analysis of feathers is 
still unclear, and may not correspond to the exact 
locations where the birds were captured. 
Taiwan Yuhinas and Steere’s Liocichlas had 
significant yearly variations in 5 ,5 N values in this 
study. Thus, the differences in 5 ,5 N values of the 
feathers of these species suggest that, from 1 year 
to the next, these birds either fed at different 
altitudes or remained at the same location but 
changed the composition of their diet, or remained 
at the same location and did not change the 
composition of their diet, but 8 I5 N values of the 
diet varied (Dalerum and Angerbjorn 2005). 
Our attempt to separate individuals from 
different altitudes and to establish a sound isotope 
profile along the altitudinal gradient using feather 
carbon and nitrogen isotope was unsuccessful. 
Thus, these two isotopes do not appear to be 
suitable for the study of altitudinal migration of 
montane passerines in Taroko. First, we found 
either no significant differences between sites, or 
significant differences between some, but not all 
sites when investigating 8 l5 N, and 5 I3 C separately 
or together regardless of whether the data are 
analyzed at the guild level or species level. 
Second, feathers reflect isotopic values at the 
time and location of molt (Chamberlain et al. 
1997, Hobson and Wassenaar 1997, Wassenaar 
and Hobson 1998, Hobson 1999b, Wassenaar and 
Hobson 2000) and the application of stable 
isotopes to study bird migration relies on sound 
information of isotopic values across their altitu¬ 
dinal range. However, not only did we find 
instances where there were weak relationships 
between feather 5 I5 N, 5 13 C, and altitude, but even 
where there was a significant relationship, the 
amount of variation explained by the relationships 
(R 2 ) was quite low. This is also the case in 
previous studies (Graves et al. 2002, Hobson et al. 
2003, Mannel et al. 2007), although these studies 
suggested that 5 I5 N and 5 I3 C might be useful for 
studying the altitudinal movements of animals. 
While these studies found significant relationships 
between feather 5 13 C or feather 5 I5 N and altitude, 
they did not indicate the R 2 value or discuss the 
predictive strength of the relationship. In contrast, 
our study suggests that carbon and nitrogen 
isotopes are not adequate to serve as regional 
markers of individuals or populations inhabiting 
different altitudes. While feather carbon and 
nitrogen isotopes exhibit a significant altitudinal 
trend for some guilds or species; it is not strongly 
predictive and does not appear to be useful for 
tracking altitudinal movement of montane passer¬ 
ines. 
ACKNOWLEDGMENTS 
We greatly appreciate B. V. Chu, Jian Hong Chen, Jia 
Hong Chen, and H. Y. Lin for help with fieldwork, and 
Talita Alencar, A. M. Johnson, and Jenilyn Weston for 
feather cleaning and sample preparation. We thank David 
Tingey for assistance with the isotope analyses. We are 
grateful to Ellen Paul for help and support with feather 
shipments. We thank Taroko National Park of Taiwan for 
financial and logistic support. This study was also 
supported by grants NSC 96-2621 -B-024-001 from the 
National Science Council of Taiwan to HJS. 
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