Chang et al. • ALTITUDINAL CHANGES OF 8 15 N AND S 13 C IN MONTANE BIRDS 43 
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S 15 N ( 0 /„ o ) 5 13 c (°/J 
FIG. 7. Continued. 
these two species in feathers grown in 2007 were 
significantly higher than those grown in 2006 
(Fig. 7, Table 2). The power of these tests varied 
between 0.05 and 0.43. 
DISCUSSION 
Altitudinal Trends in Feather S ,5 N and S 13 C 
Values .—A major finding was that there is no 
simple relationship between feather isotope values 
and altitude. Feather 8 15 N values decreased 
significantly with increasing altitude for insecti- 
vores, but not for herbivores and omnivores. 
Feather 8 13 C values increased significantly with 
increasing altitude for herbivores and omnivores, 
but not for insectivores. Altitudinal trends in 
feather 8 15 N and 8 ,3 C values exhibited more 
inconsistent patterns when analyzed by species; 
feather 8 15 N and 8 13 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. 
In addition, these patterns do not reflect those 
typically reported for plants and soils (Mariotti et 
al. 1980; Korner et al. 1988, 1991; Marshall and 
Zhang 1994; Sparks and Ehleringer 1997; Schuur 
and Matson 2001; Amundson et al. 2003), i.e., 
5 13 C values increasing (—1.1 %o/km) (Korner et 
al. 1991), and 8 I5 N values decreasing (—1.6 %o/ 
km) (Mariotti et al. 1980; Handley et al. 1999; 
Jacot et al. 2000a, b; Schuur and Matson 2001; 
Amundson et al. 2003; Mannel et al. 2007) with 
increasing altitude. 
The mechanisms responsible for altitudinal 
patterns in feather 8 I3 C and 8 I3 N values are still 
not understood, but the altitudinal patterns of 
feather 8 I3 C and 8 15 N values could be interpreted 
by several interrelated hypotheses involving 
nutrition. First, 8 I3 C and 8 I5 N values of plants 
(Mariotti et al. 1980; Handley et al. 1999; Jacot et 
al. 2000a, b; Amundson et al. 2003; Mannel et al. 
2007) and arthropods (Markow et al. 2000, 
Herrera et al. 2002, Hood-Nowotny and Knols 
2007) exhibit interspecific differences. Previous 
studies conducted in Taroko show that plant (Xu 
and Lin 1984, Chen 1994) and insect (Xu 2006, 
2007) species change with altitude. Assuming 
these birds stay locally at their molting sites, 
perhaps the lack of altitudinal patterns in feather 
S I3 C and 8 I5 N values in many of the species we 
