On the relationship among birds and Trema micrantha in montane forests of Hispaniola

Abstract

Avian frugivores are of great interest to ecologists because they play an important role in ecosystem functioning, and can serve as important components in habitat restoration. In the Neotropics, observational studies have demonstrated the importance of a variety of fruit trees to numerous bird species, but undoubtedly other tree species exist that are a key resource for birds. I explored the relationship between Trema micrantha (L.) Blume, which produces superabundant fruit nearly continuously, and its disperser assemblage in Hispaniolan pine forest and montane broadleaf forest in the Sierra de Bahoruco, Dominican Republic. In 174 hours of observation at sixteen trees I recorded 513 visits by nineteen species of birds. Birds did not visit Trema in numbers reflecting their relative abundance in each habitat. The most frequent consumer of Trema fruit was the migratory Cape May Warbler, Setophaga tigrina (Gmelin, 1789), but other frequent visitors included the Black-throated Blue Warbler, S. caerulescens (Gmelin, 1789), and the endemic Palmchat, Dulus dominicus (Linnaeus, 1766), and Hispaniolan Highland-Tanager, Xenoligea montana (Chapman, 1917). I recorded 85 aggressive interactions among nine species of birds in Trema trees, with female Cape May Warblers involved in most of these. There was no evidence that Trema was dependent on any one species of bird for dispersal of its seeds, and despite the large proportion of visits by the Cape May Warbler, I found no evidence that any species of bird was dependent upon fruit from Trema. Rather, because male Cape May Warblers dominate females and defend nectar sources in these habitats, I suggest that for female  Cape May Warblers, these scattered Trema trees represent a known, reliable, and accessible source of food which they can defend. Trema trees will benefit these bird species as a food resource, but may also function as a target for many other birds moving across the landscape, thereby facilitating the dispersal of a wider variety of seeds and the restoration of deforested sites.