Morphological and isotope data on three passerines in Taiwan

The niche variation hypothesis (NVH) predicts that populations with wider niches exhibit greater morphological variation through increased inter-individual differences in both niche and morphology. In this study, we examined niche-trait relationships in three passerine species (Cyanoderma ruficeps, Sinosuthora webbiana, Zosterops simplex). A total of 289 C. ruficeps from 7 sites, 259 S. webbiana from 8 sites, and 144 Z. simplex from 6 sites were sampled along an elevation gradient (0-2,700 m) in Taiwan from 2009 to 2017. We measured bill traits (length, width and depth of bill) and body-size traits (length of head, tarsus and wing) of the birds, which were reduced to four principal components (bill PC1, bill PC2, body-size PC1, body-size PC2). We collected feather tissues for stable carbon and nitrogen isotope analyses to quantify their isotope niche. We quantified inter-individual differences in isotope space and trait space with four diversity metrics (divergence, dispersion, evenne...