On the use of stable hydrogen isotope measurements (δ2 h) to discern trophic level in avian terrestrial food webs

Abstract

The measurement of stable hydrogen isotope ratios (δ2 H) in animal tissues is a popular means of inferring spatial origins and migratory connections. However, the use of this isotope to infer diet and potentially trophic position remains poorly understood, especially in non-aquatic terrestrial ecosystems. In many animal communities, tissue δ15 N values are strongly associated with trophic position. Correlations between tissue δ2 H and δ15 N are expected, then, if δ2 H is affected by trophic enrichment of2 H. In addition, within sites, we would expect higher tissue δ2 H values in insectivorous species compared to granivores or nectarivores. We tested these hypotheses for two resident avian communities in Nigeria consisting of 30 species representing a range of dietary guilds (granivores, frugivores, nectarivores, omnivores, insectivores) by comparing feather δ2 H, δ15 N and δ13 C values. We found considerable isotopic overlap among all guilds except granivores, with no clear pattern of enrichment in2 H with trophic position. However, at one of our sites (open scrubland), feather δ2 H was positively correlated with feather δ15 N (R2 = 0.30) compared to a closed canopy forest site (R2 = 0.09). Our results indicate weak evidence for predictable trophic enrichment in2 H in terrestrial environments and indicate that controlled studies are now required to definitively elucidate the behavior of H isotopes in terrestrial food webs.