The Wilson Journal of Ornithology 123( 1 ):33—47, 2011 
STABLE NITROGEN AND CARBON ISOTOPES MAY NOT BE GOOD 
INDICATORS OF ALTITUDINAL DISTRIBUTIONS OF 
MONTANE PASSERINES 
YUAN-MOU CHANG, 1 KENT A. HATCH, 2 HSIN-LIN WEI, 1 HSIAO-WEI YUAN, 3 
CHENG-FENG YOU, 4 DENNIS EGGETT, 5 YI-HSUAN TU, 6 YA-LING LIN, 7 AND 
HAU-JIE SHIU 1 - 8 
ABSTRACT.—We examined 5 I5 N and 8 I3 C values of feathers from nine species, belonging to three feeding guilds 
(herbivores, omnivores, and insectivores), of wild passerines at eight sites along an altitudinal gradient (339-2,876 m asl) 
within Taroko National Park, Taiwan. We examined: (1) if altitudinal patterns in feather § 15 N and 5 I3 C are consistent with 
previously published values for plants and soils, (2) if feather 5 15 N and 8 13 C differ among sites, and (3) if there are year-to- 
year and/or month-to-month fluctuations in feather 8 I5 N and 5 I3 C of the same birds. We found no simple relationship 
between feather isotope values and altitude. Feather 8 I5 N values decreased significantly with increasing altitude for 
insectivores, but not for herbivores and omnivores. Feather S I3 C values increased significantly with increasing altitude for 
herbivores and omnivores, but not for insectivores. Altitudinal trends in feather 5 I5 N and 8 I3 C values exhibit even more 
inconsistent patterns when data were analyzed by species; feather 8 ,5 N and 5 I3 C values for some species increased 
significantly with increasing altitude, others decreased significantly with increasing altitude, and still others exhibited no 
significant relationship between isotopic values and altitude. The R 2 for the relationship between feather 8 I5 N, 8 13 C values 
and altitude was generally low regardless of whether the analysis was by feeding guilds or species. This indicates much of 
the variation cannot be explained by altitude. There were either no significant differences between sites, or significant 
differences between some but not all sites when investigating 8 15 N or 8 I3 C, whether by feeding guilds or by species. Our 
study suggests that carbon and nitrogen isotopes may be not useful markers to track altitudinal migration of montane 
passerines. Received 16 April 2010. Accepted 15 September 2010. 
Stable isotope analysis in animals is a powerful 
tool in reconstruction of diets (Hobson and Clark 
1992), trophic levels (Kelly 2000), feeding 
habitats (Hobson and Sealy 1991, Cherel et al. 
2000), and in understanding migration patterns 
(Hobson 1999b, Webster et al. 2002, Rubenstein 
and Hobson 2004, Hobson 2005). Feathers are 
particularly appealing material for use in stable 
isotope studies of the migratory ecology of birds 
1 Department of Ecoscience and Ecotechnology, National 
University of Tainan, 33 Su-Lin Street, Section 2, Tainan 
70101, Taiwan. 
2 Biology Department, C.W. Post Campus of Long Island 
University, 720 Northern Boulevard, Brookville, NY 
11548, USA. 
3 School of Forestry and Resource Conservation, National 
Taiwan University, Number 1, Section 4, Roosevelt Road, 
Taipei 106, Taiwan. 
4 Department of Earth Science, National Cheng Kung 
University, Number 1, University Road, Tainan 70101, 
Taiwan. 
^Department of Statistics, Brigham Young University, 
230 TMCB, Provo, UT, 84602, USA. 
6 Department of Statistics, National Cheng Kung Univer¬ 
sity, Number 1, University Road, Tainan 70101, Taiwan. 
7 Department of Life Sciences, National Cheng Kung 
University, Number 1, University Road, Tainan 70101, 
Taiwan. 
8 Corresponding author; e-mail: shiuhj@mail.nutn.edu.tw 
because they are metabolically inert after synthe¬ 
sis. Isotopic signatures of both temporal and, if the 
animal is moving, spatial scales are, therefore, 
permanently recorded in the feathers (Chamber- 
lain et al. 1997, Hobson and Wassenaar 1997, 
Hobson 1999a, Kelly 2000, Wassenaar and 
Hobson 2000, Kelly et al. 2002, Rubenstein et 
al. 2002, Dalerum and Angerbjorn 2005). Despite 
the wide application of stable isotopes to ques¬ 
tions of animal migration, the potential value for 
examining altitudinal migration has been little 
studied (Graves et al. 2002, Hobson et al. 2003, Yi 
and Yang 2006, Mannel et al. 2007). 
Studying altitudinal migration using stable 
isotopes relies on variation in isotopic signatures 
over an altitudinal gradient. In plants, 5 I3 C values 
typically increase with increasing altitude which 
is related to plant physiological adaptation to 
changes in CO 2 partial pressure, soil moisture, 
ambient humidity, and air pressure with altitude 
(Komer et al. 1988, 1991; Marshall and Zhang 
1994; Sparks and Ehleringer 1997). In contrast, 
5 15 N values in plants and soil decrease with 
increasing altitude due to the influence of lower 
temperatures, lower pH, and higher precipitation 
at higher altitude (Mariotti et al. 1980, Schuur and 
Matson 2001, Amundson et al. 2003). The isotope 
patterns at the base of the food chain can be 
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