2016 Volume 19 Issue 1 Pages 13-20
Since 2005, Oriental white storks Ciconia boyciana have been continuously reintroduced by Hyogo Park of the Oriental White Stork (HPOWS) in the Toyooka Basin, Japan. However, most of them remain strongly dependent on hand-feeding in HPOWS after release because they can thereby obtain highly nutritious fish (Trachurus japonicus, Oncorhynchus mykiss, etc.). In contrast, a few storks are independent of hand-feeding, preying on various animal species (such as fish, frogs, insects, crustaceans) in the Toyooka Basin. However, this information on the foraging of reintroduced storks is on the basis of behavioural observations, but their trophic levels and food habits are unclear. Stable isotope analysis can be useful for estimating feeding habits. Therefore, we analysed carbon and nitrogen stable isotope ratios (δ13C and δ15N) in feeding-dependent storks (FDS) and -independent storks (IS), and then compared these values with those of captive-bred storks (CBS). The stable isotopic analysis showed that the levels of δ13C and δ15N were in the fol lowing order: CBS ＞ FDS ＞ IS. Our results suggest that the trophic level of storks rises upon strong dependence on hand-feeding; the provision of highly nutritious fish via hand-feeding thus has a major impact on the feeding habits of wild storks.
