Appendix

Appendix 1: Proving different residency categories

To prove that individuals remained for different periods throughout the non-breeding season at our study site – that individuals have different within-winter residency strategies – we compared the observed frequencies of the number of visits individuals were detected each year, with that expected by chance assuming that all individuals were long-term winter residents. To do this, we first calculated the number of individuals seen per year and the respective mean number of visits. We ran 50 iterations to obtain a representative mean of birds detected each visit, assuming that (1) birds were present in the area throughout the study, i .e . long-term winter residents, and (2) that the detection rate per visit was 0.33 (see manuscript). We then compared these estimates with our observed data using a two-sample t -test. We expect that if our observed frequencies match those expected by chance, then all individuals are long-term winter residents. If frequencies do not match, however, we assume that individuals have different duration residency periods. All years were analysed separately. Individuals seen in multiple years were not excluded from any analyses.
We repeated this same analysis using data from individuals that were observed at least twice throughout the year to eliminate individuals that were likely to be simply passage birds. By doing this, we eliminate individuals that may have been passing by and detected by chance, and not necessarily utilising resources from the area. If afterwards we still observe differences in expected and observed frequencies, then we expect that not all individuals detected at our study site are long-term winter residents.
We found that the expected frequencies of the number of visits that individuals were predicted to be detected at was statistically different from what was observed when analysing both the data set with information from all individuals and the data set with individuals that were detected at least twice during the year (Fig. A.1; Table A.1). These results are similar across years. With this, we confirm that not all birds seen at our study sites are long-term winter residents.