Bank on it

Catherine A. Lindell, Ryan S. O’Connor, and Emily B. Cohen make a contribution to what we know about songbirds’ nesting success in active and abandoned coffee plantations and active pasture. Specifically, they studied White-throated Thrushes (Turdus assimlis) and Clay-colored Thrushes (T. grayi) in Las Alturas reserve (for four breeding seasons) and Rio Negro, an active coffee farm (unfortunately, only for one season).

These two species of birds, congeners of our American Robin, do not migrate north to the U.S. to breed (there are some records in south Texas for Clay-colored Thrush), in contrast to the charismatic migratory wood warblers (used to promote shade-grown coffee) that feed in forests and plantation overstories in the winter months. The thrushes of the research prefer to nest on the ground or low in a tree. The slightly surprising results of the paper are that nesting success is only indirectly affected by type of land cover, and the effect is through how well the terrain provides concealment from predators. In particular, nesting in a steep bank in pastureland provides the greatest protection (the nest can’t be detected from below, and cattle can’t trample it).

There is a scintilla of a hint that the birds can be more successful in an active coffee plantation—more humans means fewer predators—but keep in mind that only one year of data is available.

I’ll let the authors summarize the research’s conservation implications:

Conservation recommendations based on land-cover type would be relatively easy if we could rank land-covers as to the quality of habitat they provide for target species and if rankings were consistent across species. Our results indicate these conditions are not met for these species.