Survival, Dispersal and Initial Migratory Movements of Juvenile Great Spotted Cuckoos Clamator glandarius

The Great Spotted Cuckoo Clamator glandarius belongs to the family Cuculidae, whose biology has been intensively studied for years, particularly in the context of avian brood parasitism. However, there are still important gaps in knowledge of its biology. Recent studies have highlighted the absence of information about survival, dispersal and migratory routes of juveniles, and the main aim of this study was to contribute to filling this gap. We used radio-transmitters and satellite tags (pTTs) to study the initial movements of juvenile Great Spotted Cuckoos in the study area (i.e. breeding territories), as well as their long-distance migratory movements. We found that a large proportion of marked individuals died in the study area within days or weeks of leaving the nest, with direct and indirect evidence suggesting that predation is the main cause of mortality. Our results suggest that pre-migratory movements of juveniles, i.e., those carried out before leaving the Iberian peninsula, are different from those previously found for experienced adults. The high predation rate in the study area meant that only three of 13 satellite-tagged juveniles initiated migration to their wintering area in sub-Saharan Africa, using the Eastern Atlantic route. Overall, the information provided here contributes to a better understanding of the biology of juvenile great Spotted Cuckoos and could be useful in addressing potential future conservation problems.