STABLE ISOTOPE ANALYSIS

METHODS

We collect samples for stable isotope analysis during the breeding season at the study area near Teshekpuk Lake. Birds are first captured in mid-June and we take blood samples of birds during the time when females are forming eggs. We then search for nests and remove one fresh egg per nest. We then capture the female on the nest to collect feather and claw samples. Once the chicks have hatched we collect all the remaining eggshells and membranes. Furthermore we take samples of the local food chain by collecting invertebrates from the mud in shallow lakes in the study area.

We use red blood cell isotopic signatures as an index of body reserves, and plasma isotope ratios as an index of locally ingested food. The isotope ratio of egg material is then compared to these two endpoints to determine which source is more important.

We then use the head feathers and claw tips of females to determine where they spent the previous winter. By using birds with satellite transmitters we were able to establish an accurate relationship between feather isotope ratios and wintering regions in the Bering Sea that can be applied to females captured on the nest.

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