Spring Migratory Stopover of Swainson's Thrush Along the Pacific Coast of Southwest Costa Rica

Abstract

Abstract Stopover behavior and migratory pathways of neotropical migrant birds in Central and South America have received little study. We examined stopover ecology of Swainson's Thrush (Catharus ustulatus) on the Osa Peninsula, Costa Rica, during spring migration, 2002–2005. Capture rates per net hour were high (;amx = 21.8 individuals/100 net hrs) suggesting large numbers pass through lowland coastal areas in spring. Mean passage date of males was ∼6 days earlier than females. Timing of passage by age class was variable; after-second year (ASY) birds preceded second-year (SY) birds in 2 years, SYs preceded ASYs in 1 year, and both had the same mean passage date in 1 year. We also observed annual variation in relative abundance of the two age groups. Only 1.7% of marked Swainson's Thrushes were recaptured on subsequent days suggesting most individuals left the immediate area soon after initial capture. Stopover lengths ranged from 1 to 9 days, although most were <4 days. Many individuals had some energy ...