Is the settlement of a winter territory in the European Robin Erithacus rubecula triggered by the arrival of conspecific migrants?

Abstract

European Robins are well known for defending a winter territory. Both resident birds and newly arrived migrants defend a winter territory. However, little is known about the timing and drivers of the settlement of the winter territory in autumn. We hypothesized that settlement is triggered by the arrival of migratory Robins from the North. The hypothesis was tested by relating observational data on first autumn song (as indicator for the settlement of a winter territory) of European Robins in a back yard in the North of the Netherlands to nationwide arrival dates of migratory European Robins in the Netherlands. Date of first autumn song in the studied yard advanced significantly with 14 days from 1993 to 2021, but there was no significant relationship with nationwide autumn arrival dates. We conclude that first autumn song (as indicator of settlement of winter territory) in European Robin does not seem to be triggered by the arrival of (conspecific) migrants. We suggest instead that advanced timing of breeding caused the advancement of winter territory settlement. Climate change may allow resident Robins to moult earlier and settle before conspecific migrants arrive. However, this suggestion needs further testing.