Revising the convergence hypothesis of avian use of honeydew: evidence from Dominican subtropical dry forest

A honeydew-producing scale insect (family Margarodidae, tribe Xylococcini, genus Stigmacoccus) was found associated with the tree Bursera simaruba in subtropical dry forests at elevations of 100-400 m on the south side of the Sierra de Bahoruco, Pedernales Province, Dominican Republic. At two study sites, 91% of Burseia trees supported locally dense populations of Margarod idae. Fifteen species of birds were observed foraging on the honeydew, but most observations were of the winter resident Cape May warbler (Dendroica t igrina) and black-throated blue warbler (D. caerulescens), and the permanen t resident bananaquit (Coereba flaveola) and black-crowned palm tanager (Ph aenicophilus palmarum). The Cape May warbler actively defended the honeydew resource but frequency of use of honeydew was influenced by the close pres ence of flowering agave and scale insect density. Data suggest that honeyde w may be a critical component of the diet of this species especially during the late winter dry-season. Hymenopteran insects also were observed feedin g on honeydew, but rates of consumption did not approach that of avian spec ies. The occurrence of this phenomenon in Dominican dry forest is discussed in light of the convergence hypothesis of bird use and defense of homopter an honeydew in which it is proposed that birds are able to maintain relatio nships with scale insects in moist, warm temperate forests because it is in these climates where ant abundance is low. We suggest that our observation of a well-developed bird-homopteran system in classic subtropical dry fore st supports the proposed mechanism of reduced competition with ants allowin g bird use of honeydew, but we suggest that a broader array of especially i nsular habitats which may be relatively depauperate in terms of ants also c an be expected to support bird-homopteran systems.