Transient swainson's thrush (Catharus ustulatus) wintering in the andean foothills of Ecuador are almost exclusively young males

We know relatively little about the non-breeding period of most migratory birds. Decades of research on Swainson's Thrush (Catharus ustulatus) have focused on their breeding ecology, whereas their non-breeding ecology is limited to broad patterns of distribution and migratory stop-over ecology. For nearly 50 years, the US Breeding Bird Survey recorded declines of 0.7% per year for the Russet-backed Swainson's Thrush (C. u. swainsonii) subspecies, which spends the non-breeding period in South America. However, there is an insufficient understanding of the constraints across their annual cycle to determine the reasons for the sustained decline. In 2013 and 2014, we exam-ined their little studied non-breeding period on the Andean slopes of Ecuador, where prior experience showed that they were seasonally abundant. Here, rapid deforestation threatens primary forests. We used point counts and radio telemetry to evaluate whether the primary forests were preferentially used in relation to recently regenerated second-growth forests. From point counts, 76% of detections and almost all captured individuals occurred in secondary forests. Of 86 birds captured in mist nets, 85 were males and 83 were young, indicating a high-ly skewed ratio in favor of young males. Radio telemetry demonstrated a preference for the secondary forest, especially for fruiting Cecropia spp. trees, with no apparent territorial behavior by those tracked and with short residency times. A marked decrease in density over the course of the field season suggests an itinerant population possibly tracking ephemeral fruit resources. Alternatively, these temporal and spatial patterns could suggest that this population undergoes a mid-winter intra-tropical migration, or at least landscape-level movements. However, we observed thrushes throughout our extended sampling period, suggesting transiency with high turnover. This study documents demographic separation during the non-breeding period with preference for secondary forests and high transiency, important findings in informing management across the annual cycle.