Sr isotope analysis of bird feathers by TIMS: a tool to trace bird migration paths and breeding sites

Here we present a methodology to analyse Sr-87/Sr-86 isotope ratios in bird feathers with very low Sr concentration using ultra-low blank ion-exchange chemistry combined with thermal ionisation mass spectrometry. For this study, Sedge Warbler (Acrocephalus schoenobaenus) feathers were used from four different locations within Europe. Prior to analyses, dust particles from the feathers' surface were removed with nitrogen gas. The shaft and the vane parts of the feather were analysed separately. Generally, the vane had higher trace element abundances compared to the shaft. The vane contained between 3 ng and 12 ng of Sr and the shaft between 0.5 ng and 3 ng of Sr. Due to the small amount of Sr in the feathers, small loads (0.5-12 ng Sr) of international standard NBS 987 were analysed for Sr-87/Sr-86 isotope ratios giving an average of 0.710263 +/- 0.000013 (2 sigma) (n = 177) and an external reproducibility below 0.002%. The average Sr-88 beam intensities for all the shaft analyses were 0.79 V while for the vane analyses it was 2.7 V, consistent with the measured Sr contents of the feather shafts and vanes. The Sr-87/(86) Sr isotope ratios of the vane were more precise than the shaft with 2 SD internal precision of 0.0026% and 0.053%, respectively. However, the precision was adequate for resolving Sr isotope variations between localities. The Sr-87/Sr-86 isotope ratios of the cleaned Sedge Warbler feathers varied geographically and were indicative of the different geology in the locations where the feathers were grown.