Stable carbon isotope ratios as indicators of marine versus terrestrial inputs to the diets of wild and captive tuatara (Sphenodon punctatus)

Stable carbon isotope analysis was used to examine feeding relationships of wild tuatara on Stephens Island and captive tuatara in New Zealand institu tions. We first measured delta(13)C in three food items of wild tuatara. Pe ctoral muscle of fairy prions (a seabird eaten seasonally by tuatara) was s ignificantly enriched in C-13 compared with whole bodies of wild insects (d arkling beetles and tree weta). Values for delta(13)C in blood cells varied significantly among wild tuatara of different life-history stages. Male tu atara were more enriched in C-13 than were females or juveniles, suggesting that males prey more heavily on seabirds. Insect foods of captive tuatara varied dramatically in delta(13)C; this is attributed to differential consu mption of plant material derived from the C-3 and C-4 photosynthetic pathwa ys. Blood cells from four different groups of captive tuatara differed sign ificantly in delta(13)C. This was perhaps related to assimilation of insect s with different delta(13)C values, and cannot be attributed to differences in seabird predation as captive tuatara do not have access to seabirds. Fo r wild tuatara on Stephens Island, stable carbon isotope analysis provides support for the dietary information available from behavioural observations , gut analyses and measurements of plasma composition.