The relative importance of native forest and shade-grown coffee plantations for habitat use, individual fitness and migration strategies of overwintering Neotropical migrant songbirds in Colombia

Winter habitat quality is one of the primary ecological factors limiting self-maintenance and survival of Nearctic-Neotropical migratory birds during the non-breeding season. I assessed the relative importance of shade-grown coffee plantations vs. forest in the Colombian Andes as winter habitat for Swainson’s Thrush (Catharus ustulatus), Gray-cheeked Thrush (Catharus minimus), and Canada Warbler (Cardellina canadensis). For Swainson’s Thrush, I used daily and seasonal mass change, age ratios, density and corticosterone levels as measurements of habitat quality; and for Canada Warbler I used daily and seasonal mass change and sex ratios. Automated radio-telemetry on a continental scale was used to determine the effect of overwintering habitat occupancy on spring departure date and migration pace of Swainson’s Thrush. Using light-level geolocators I assessed the link between winter habitat occupancy and migratory connectivity of Gray-cheeked Thrush, and measured population spread and its relationship with the species winter distribution. I determined migratory connectivity of Canada Warblers overwintering across the three Andean cordilleras in Colombia by analysing stable hydrogen- isotope values (δ2H) in feathers. Taken together, my results suggested that native forests are more suitable winter habitats than shade-grown coffee plantations for Swainson’s Thrush. Native forest maintained a higher number of individuals than coffee, and in general, individuals maintained or increased their daily and seasonal body condition. On the other hand, the results for Canada Warbler are not conclusive, the quality of coffee can improve in certain circumstances such as high precipitation. My research provides the first evidence that by overwintering in native forest, birds can adjust their departure date, migration speed, and fuel up sufficiently to cover about 25% of the total length of spring migration. Migratory connectivity revealed that the effect of land-use changes on the wintering grounds is likely to be amplified on the breeding grounds through strong migratory connectivity. While market-based conservation strategies primarily promote shade-grown coffee plantations for the conservation of Neotropical migrants, my research suggest that strategies to conserve and restore native forest are also urgently needed