Determining the Sources of Calcium for Migratory Songbirds Using Stable Strontium Isotopes

• Published in: Oecologia 2001-02, Vol.126 (4), p.569-574
• Main Authors: Blum, Joel D., Taliaferro, E. Hank, Holmes, Richard T.
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Animals; Autoecology; Aves; Biological and medical sciences; Bones; Calcium; Ecosystems Ecology; Eggs; Eggshells; Female animals; Fundamental and applied biological sciences. Psychology; Ratios; Songbirds; Strontium; Thermoregulation. Hibernation. Estivation. Ecophysiology and environmental effects; USA, New Hampshire; USA, Vermont; Vertebrata; Vertebrates: anatomy and physiology, studies on body, several organs or systems; Warblers; Winter
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/s004420000550

We investigated natural variations in the stable isotopic composition of strontium (a surrogate for calcium) in the bones of a single species of breeding migratory songbird, as well as in their eggshells, egg contents, and food sources. We use this information to determine the sources of calcium to these migratory songbirds and their offspring. Samples were collected from two locations in the northeastern USA (Hubbard Brook, NH, and Downer Forest, VT.) that differed in soil geochemistry. The mean87Sr/86Sr ratios of food items (caterpillars and snails), eggshells, and egg contents were indistinguishable within each site, but significantly different between the two sites. Mean87Sr/86Sr ratios for the bones of adult females were significantly different between the two sites, but values were significantly lower than those of food items and eggshells at each site. Two of four adult individuals studied at each site had87Sr/86Sr ratios lower than the entire range of values for local food sources. Mixing calculations indicate that up to 60% of skeletal strontium and calcium was derived from foods consumed in the winter grounds where lower87Sr/86Sr ratios predominate. At each study site, the87Sr/86Sr ratio of eggshells differed significantly between clutches, but the mean clutch87Sr/86Sr ratios were unrelated to the skeletal87Sr/86Sr ratio of the laying adult. These findings suggest that strontium (and hence calcium) for eggshell production in this species is derived predominantly from local food sources in breeding areas. Thus, reductions in available calcium in northern temperate ecosystems due to the influences of acid deposition could be potentially harmful to this and other species of migratory bird.