How do Robins Erithacus rubecula resident in Iberia respond to seasonal flooding by conspecific migrants?

Abstract:
Capsule The majority of Robins in Iberia are sedentary and stay in their nesting areas despite the pre- sumed increased competition that results from the seasonal flooding of the area by conspecific migrants. Aims To evaluate if Robins in Iberia are displaced from their nesting areas by the presence of large num- bers of competitors originating from higher latitudes.

Methods Data from constant effort ringing sites were used to estimate the proportion of Robins that are strictly sedentary and the seasonal variation in Robin numbers. Hydrogen stable isotope ratios (d2H) in feathers, and sex ratios determined through molecular techniques, allowed an insight into the numerical importance of invading Robins from higher latitudes.

Results Robins were more numerous outside the breeding season, with clear influxes in autumn. Around half of the locally nesting Robins were captured during winter, indicating they are truly sedentary. d2H in feathers suggests that a wide mixture of Robins from all European latitudes were present in winter, and these data, together with sex ratios, suggest that there may be similar numbers of local and foreign individ- uals in winter at the main study site.

Conclusion Despite the occupation of their range by migrants, local birds are largely sedentary.