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Where do the birds go? Multi-isotopic tracing of European-breeding migratory birds

Final Report Summary - MIGRATE (Where do the birds go? Multi-isotopic tracing of European-breeding migratory birds)

Gotland study

Radiogenic strontium (Sr) and stable (delta-H-2 and delta-C-13 - delta-N-15) isotope ratios were measured in single feathers (n = 60) from nestling Pied Flycatchers in six different sites (3 - 4 nests per site) within the island of Gotland in Sweden. Gotland's geology is characterised by a sequence of Silurian shales / limestones and sandstones. The variability in Sr isotope ratios in the bedrock is expected to be reflected in the bioavailable Sr in the environment and in the feathers. The aim is to test the resolution of Sr isotopes alone and in combination with stable isotopes to locate the sites where feathers grew in a small region. Bed rock, soils, water and vegetation were sampled in the proximity of the nests to determine the 87Sr / 86Sr of the bioavailable Sr in each site. Our data show that the 87Sr / 86Sr feathers plot between the 87Sr / 86Sr of water and vegetation / soil leachates. Feathers from all the sampling regions show significant variation in 87Sr / 86Sr (0.710 - 0.722). Pied Flycatchers are insectivorous birds and feed their nestling with prey hunted close to the nest. Thus, we do not expect large variability in stable isotope ratios do to the proximity between study sites within Gotland. However, delta-H-2 isotope ratios measured in single feathers for each site show a large range between -57 and -98 compared to the annual weight delta-H-2 of precipitation in the area (-53 and -80). This is probably due to the fact that the delta-H-2 of nestling's feathers reflects the composition of the diet consisting of insects (with more negative delta-H-2 values) and not a combination of insects + drinking water (with more positive delta-H-2 values similar to delta-H-2 of precipitation). Mean delta-N-15 values of nestling feathers range between 7.1 to 10.8 increasing towards the sites in the SW probably due to the influence of sea spray. Mean delta-13-C values of nestling feathers are very similar among sites ranging in total between -21.2 to -22.8 typical values of C3 type plants.

Conclusions

On a regional scale 87Sr / 86Sr composition of Pied Flycatcher feathers and of the bio-available Sr do not correlate with the 87Sr/86Sr composition of the bedrock geology. 87Sr / 86Sr composition of the feathers generally plot between 87Sr / 86Sr composition of water samples and vegetation / soil leachates. The delta-H-2 values of the Gotland feathers show a larger range compared to the delta-H-2values of annual precipitation probably do to the diet of nestlings. The delta-N-15 composition of the feathers in Gotland increases towards the SW probably due to seaspray. Delta-C-13 values of nestling feathers are typical values of C3 plants which are compatible to the type of plants available in northern latitudes.

Potential impact and socio-economic impact of the project

Detailed quantification of changes in migratory bird behaviour is still problematic. Linking breeding and wintering sites of different populations of migrant birds and establishing how migratory behaviour is changing is an urgent priority in assessing climate-change effects on bird biodiversity. In addition, there is a vital need to accurately establish the origins of migratory bird species to better monitor and hence control the dispersion of zoonotic diseases such as avian flu. This study is designed to assess the viability and accuracy of a combination of state-of-the-art radiogenic and stable isotopes techniques as a non-invasive method to trace migratory birds whereabouts. This novel method offers the prospect of radically improving our ability to map the whereabouts of migratory birds with great spatial resolution.

The isotopic technique can also be applied to other disciplines for provenance studies, like in archaeology and forensics sciences. The results achieved in this study are directly applicable to other disciplines.

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