LIGHT AS A (SIBERIAN) FEATHER: USING FEATHER GEOCHEMISTRY TO INTERPRET BIRD BEHAVIOR AND MIGRATION IN WESTERN JAPAN

Geochemists have spent more than 50 years mapping patterns of stable isotopes in the aquatic and terrestrial landscape. Combined with recent work in ecology these patterns reveal a good deal about animal behavior and migration. This approach is applied to a collection of feathers from western Japan retrieved as dropped feathers or from the Yonago Waterbird Sanctuary (Tottori, Japan). Most feathers in this study are contour feathers.

Carbon and nitrogen isotope ratios reflect two features: a) trophic level and b) the environmental context of the food resources. Trophic level is seen primarily in the increase d¹⁵N with each step up the food chain. Birds with diets primarily based on insects and non-agricultural plants, e.g. warblers and flycatchers, have low d¹⁵N values. Highest nitrogen isotope values are seen in the fish-eating birds such as herons and cormorants. Some elevated d¹⁵N values, such as a White Fronted Goose (Anser albifrons) at +13‰, may have resulted from feeding on agricultural products. Songbirds have a very limited range in the d¹³C of feathers compared to waterbirds. Tundra swan (Cygnus columbianus) feathers range in d¹³C from -11 to -27‰ VPDB, reflecting diets dependant on seagrasses in some regions and terrestrial or aquatic plants in other locations. In Pintails (Anas acuta) d¹³C values near -10‰ probably reflect C4 agricultural crops. The greater variance in both d¹³C and d¹⁵N also reflects the much larger variance in the average carbon and nitrogen isotope ratios of organic matter in water bodies in comparison to terrestrial ecosystems.

Non-exchangeable hydrogen isotope ratios in feather keratin primarily reflect drinking water. The most negative dD values are from Whooper swans (Cygnus cygnus), which breed and molt in wetlands of the Russian Far East. The next most negative dD values are in Tundra Swans, which molt at higher latitudes than Whooper Swans, but Tundra Swans breed in coastal areas and use brackish waters and food resources. Cormorants and other marine predatory birds, such as Streaked Shearwater (Calonectris leucomelas) and Blackheaded Gull (Larus ridibundus) have the most positive dD values, reflecting the ingestion of significant amounts of seawater in food or as drinking water. Local birds vs. long distance migrants are best seen in the hydrogen isotope patterns in feathers.