Shade coffee or native forest? Indicators of winter habitat quality for a long-distance migratory bird in the Colombian Andes

Neotropical migratory songbirds overwintering at mid elevations in the Andes of northern South America depend on remnants of native forest and shade-grown coffee plantations. The quality of such habitats is one of the primary ecological factors limiting survival of migratory birds during the non-breeding season. We assessed the relative quality of shade-grown coffee plantations vs. forest in the Colombian Andes as winter habitat for Swainson's Thrush (Catharus ustulatus). We hypothesized that native forest has a higher intrinsic value (i.e., food abundance) than shade-coffee plantations, as native forest was the original habitat for Swainson's Thrush. We compared thrush physical condition, density, feather corticosterone values, and apparent annual survival as indicators of habitat quality in these two habitats. Measures of body condition and density were higher in forest than in shade-grown coffee, while survival was similar between habitats. This implies that forest had a higher carrying capacity than shade coffee and therefore had higher intrinsic value. Seasonal trends in body condition revealed a decline in the quality of forest with the onset of the dry season in early winter and an increase during late winter in line with increasing rainfall, suggesting that the timing of the rainy season likely offsets the negative effects of seasonal drought. Feather corticosterone levels were higher in forest, possibly as a result of a density-dependent stress response, however, we cannot rule out the effects of food availability or its distribution in space on stress levels. Our indicators suggested that native forest is a higher-quality winter habitat than shade-grown coffee. Our findings highlight how individual indicators of habitat quality can be misleading and emphasize the value of using multiple measures. While shade coffee is a critical habitat in the absence of native forest and its importance for the conservation of migratory birds is widely accepted, our results indicate that the conservation of native forest must be a conservation priority wherever possible.