The knowledge of migratory connectivity is important for understanding the potential drivers of populations and it is thus important for conservation implications. Migratory connectivity of species can be studied using exogenous, such as rings and transmitters, or endogenous markers, such as stable isotopes and trace elements. The use of trace elements has been much less frequently studied compared to stable isotopes. Trace elements can be studied from the feathers of birds and this does not necessarily require trapping of individuals. Here we studied the variation of 18 different trace elements in feathers of two long-distance trans-African migrants, willow warblers Phylloscopus trochilus and barn swallows Hirundo rustica, using body feathers of museum specimens of birds from Finnish breeding grounds. The trace elements were measured using Laser-Ablation Inductively-Coupled-Plasma Mass-Spectrometry. We show that trace element concentrations were relatively stable along the rachis within the same feather except in Ni and S, which showed a quadratic pattern. In general, variation within feathers of the same individuals was smaller than in feathers between individuals for most elements. Furthermore, concentrations of 11 trace elements showed significantly higher concentrations in willow warbler feathers collected in spring than in autumn, moulted in African wintering grounds and European breeding grounds, respectively. Last, concentrations of seven trace elements were significantly higher in the spring feathers of willow warblers compared to barn swallows. This suggests that trace elements could be used to separate moulting grounds of the birds on the larger scale within the same species, but also sampling design should be carefully considered.

The available dataset and R Script support the paper "Intra- and interspecific variation in trace element concentrations in feathers of North European Trans-African migrants", which will be published by the Journal of Avian Biology (2023).

The uploaded files are the following:

1. Trace_element_feathers.csv: this is the dataset that contains the information used in the paper's analyses. Each row referst to a measurement spot along a feather's rachis. The columns contain the following information:
   • A running index
   • An indication of which spot is being measured
   • The concentration of each of the 20 elements analysed for the paper at the given spot
   • An identifier for the feather to which the measurement spot belongs
   • An identifier for the individual to which the feather belongs
   • Season during which the feather was collected (spring / autumn)
   • Species to which the feather belonged (barn swallow / willow warbler)
   • Number of the measurement spot along the rachis
   • A code for the individual (same information as the individual identifier)
   • A code for the feather (same information as the feather identifier)
2. Trace_element_feathers_analysis.R:  this is an R file that should open the script containing our analyses. The workflow roughly follows the paper, and it is divided into sections:
   1. Data import
   2. Data cleaning and formatting
   3. Modelling
   4. Plotting

Trace_element_feathers.csv can be opened with a wide variety of programmes, such as Microsoft Excel, LibreOffice Calc or R. It is a CSV file that uses commas as separators, points as decimal separators and has a header line. Missing values are represented by "NA".

Trace_element_feathers_analysis.R can be opened with R or RStudio.