Results
The analysis of the linear mixed-effects model that contained both
mammals and birds highlighted significant variability between the two
classes for both δ 13C andδ 15N values. Further analyses were conducted on
mammal and bird data independently.
The linear mixed effects model for mammals showed a difference of -1.93
‰ (SE = 0.08) between the δ 13C values of
homogenized whole body (CWB) and the keratin outer covering (CK) Fig.
1a), but the other pairwise relationships were not significant (Table
1). These findings imply that the presence or absence of keratin outer
covering did not significantly alter the isotopic value of the
homogenized mass in either birds or mammals (Table 1). CK and CWB did
not have a significant relationship in birds.
The linear mixed effects model for birds showed a difference of -0.32 ‰
between NWB and NK (SE=0.05) (Fig. 1 b) birds, but not mammals, and the
other pairwise relationships were not significant (Table 1).