Post-fledging ecology of juvenile wood thrush in fragmented and contiguous landscapes

Dispersal ecology represents one of the remaining frontiers of ornithology. Data on pre-migratory survival of post-fledging juvenile songbirds are limited, and estimates of survival in fragmented landscapes have been scarce. Further, data on dispersal patterns and habitat use by juveniles are scarce yet critical to understanding factors affecting population dynamics and assessing breeding habitat quality. We conducted a 3-year study monitoring 89 radio-tagged fledgling Wood Thrush (Hylocichla mustelina) in central and southern Missouri. We used an information-theoretic approach to determine support for hypotheses concerning factors affecting juvenile survival. We found the most support for the effects of fledgling age, shrub density, and regional landscape on survival. We compared survival of young birds in fragmented (approximately 24% forest cover) and contiguous (>80% forest cover) regional forest landscapes. Juvenile survival during the first thirteen weeks after fledging was higher in the fragmented landscape of central Missouri (0.773 +/- 0.120) than in the contiguous landscape of southern Missouri (0.427 +/- 0.187).; To assess post-fledging habitat use by juveniles, we classified juvenile Wood Thrush locations as natal, post-natal wandering, and post-natal settled. We used an information-theoretic approach to determine support for hypotheses concerning factors affecting juvenile dispersal based on (1) location classification and (2) the amount of time spent in a settled dispersal location. We found the most support for the effects of shrub density, number of large trees/ha (≥25 cm DBH), and percent forest cover in the local landscape on whether a dispersal location would be natal, wandering, or settled. Locations where juveniles settled had greater density of woody shrubs, fewer large trees, and less forest cover in a 90-m radius than did wandering or natal locations. We found the most support for the effects of shrub density, habitat-type, and the percent of grassland and row-crop cover in the local landscape on the amount of time a bird remained settled in a dispersal location. Birds settled for longer periods in areas with higher shrub density and in areas in closer proximity to grassland and row-crops.; We suggest mid-successional and edgy forest habitats with increased cover are important to dispersing juvenile Wood Thrush for predator avoidance and may provide increased foraging opportunities. Contiguous forest landscapes with homogenous habitat may not provide sufficient cover required by juveniles dispersing from forest interior nests. Differential post-fledging survival between populations may affect our understanding of source-sink dynamics. As such, the pre-migratory juvenile period of the Neotropical migrant life cycle should be considered in conservation planning. Management of breeding habitats should include a variety of canopy openings and successional stages to benefit populations of Wood Thrush.