Telleria J.L., Perez-Tris J., Ramirez A., Fernandez-Juricic E. & Carbonell R. (2001) Distribution of Robins Erithacus rubecula in wintering grounds: Effects of conspecific density, migratory status and age. ARDEA 89 (2): 363-373

This paper studies how population density affects the dynamics of habitat occupation by Robins in a wintering area of southern Spain (Gibraltar area), and how the between-habitat distribution is influenced by the age and migratory behaviour of birds (whether they are year-round residents or wintering migrants). We studied two different habitat types: forested sites, some of which are breeding habitats of Robins, and shrubland sites, to which Robins spread their range in autumn-winter due to the arrival of migrants. As arriving migrants increased abundance in the area, new habitat patches were sequentially colonised, forested sites being the first to be occupied and the last to be abandoned (regardless they maintained breeding populations or not). In addition, the abundance of Robins tended to decrease along the autumn-winter period in the most densely populated patches, which made the among-site distribution of Robins to be progressively more uniform. Juveniles of both local and migratory populations dominated (83% of individuals) in lowlands. Local Robins were more abundant (67%) than migratory ones in montane forests, although they also contributed to the winter colonisation of lowland habitats (47%). Together, these results support that the between-habitat distribution of Robins depends not only on population density, but also on the migratory status and age of individuals attempting to get a wintering site. Therefore, if winter habitats differed in quality, these factors could influence the mechanisms of regulation of Robin populations in the non-breeding season