Thanks to Ulf Lundwall, Per Nothagen and Peter Olsson for sharing early field-work with me, and to Henning Behmann for constant encouragement in many forms. I also want to thank K. Biledgaard, V. Dierschke, R. Christensen, K. Due-Johansen, Jadwiga Gromadzka, H.-E. Jörgensen, Wlodek Meissner, Rapportgruppen ved DOF / Århus amt and B. Struwe-Juhl for winter distribution data, Paul Eric Jönsson, Stig Nielsen, Peter Olsson, Ann-Marie Thorner and one unknown German observer for sightings of colour-ringed birds, U. Brenning, V. Dierschke, J. Gromadzka and W. Meissner for suggestions and advice during the course of the work, and H. Behmann, J. Gromadzka and M. Gromadzki for bill length data. Ragnar Ericson suggested the practical solution to the problem of separating merged, non-normal distributions. And: I sincerely hope that H.-U. Rösner will take my close reading of his dissertation as a pretext for an "Auseinandersetzung" in the matters concerned! Finally thanks to the staff of the excellent library of the Ecology Building, Lund University!