Stable isotopic analysis of stuffed specimens revealed the feeding habits of Oriental Storks Ciconia boyciana in Japan before their extinction in the wild

Abstract

By 1971, the breeding populations of the oriental stork Ciconia boyciana in Japan had become extinct in wild. After long-term conservation efforts and breeding projects, Oriental Storks have been continuously reintroduced to the Toyooka Basin, their final habitat, since 2005. The restoration of shallow wetlands in river areas and paddy fields is urgently needed in the Toyooka Basin, because these areas represent the major foraging habitats for reintroduced Oriental Storks. However, limited information is available on their feeding habits prior to extinction in the wild and, thus, it is difficult to plan specific restoration targets for these foraging habitats. In the present study, we used stable isotopic analysis to compare the nutritional status of the reintroduced populations with that of the extinct populations using preserved (stuffed) specimens. The δ15N values in the extinct populations were higher than those of the reintroduced populations. The diet proportions of the extinct populations were calculated to be equally comprised of five prey items (brackish water fish, freshwater fish, amphibians, insects, and crustaceans), while the contribution of insects was remarkably higher than that of the other prey items in the reintroduced populations. We suggest that these stable isotopic trends and diet proportions reflect a decline in the trophic level of the reintroduced populations owing to the reduced prevalence of high-nutrient prey animals caused by the loss of healthy wetlands after the 1960s in the Toyooka Basin. To increase the abundance and diversity of natural prey species available to the reintroduced Oriental Storks in the Toyooka Basin, more eco-friendly paddy fields and restored wetlands are required in the current paddy and river areas, which would secure the continuity of these wetlands from sea areas to paddy areas using fishways. However, the sampling size of the extinct populations was limited and information about historical baseline changes in prey items was insufficient. Therefore, new approaches using reintroduced populations are required to plan future reintroduction projects for Oriental Storks.