Sap feeding by birds in southern Neotropical forests

Abstract

The White-fronted Woodpecker (Melanerpes cactorum) drills wells in living branches and trunks of trees and shrubs to feed on sap flows, providing an energy-rich food resource for other bird species diverse in ecological attributes and taxonomic affinities. The aim of this study was to explore the avian assemblage that consumes sap from sap wells drilled by the White-fronted Woodpecker in 4 regions of Argentina distributed along an aridity gradient (precipitation and temperature), reaching from humid forest of the Chaco in the north to scrublands and open forest of the Monte in the south. We classified sap-feeding species according to the importance of nectar in their diet (specialist, facultative, or occasional nectarivores) and their efficiency in assimilation of sucrose (the main sugar in sap). We also compared the proportion of observed sap-feeding species with diversity of potential sap-feeding birds along the geographical aridity gradient. Forty-six bird species were recorded feeding at sap wells drilled by the White-fronted Woodpecker. Proportion of sap-feeding species was similar along the aridity gradient, and the type of diet and sucrase activity were not associated with the geographical aridity gradient. However, the proportion of occasional nectarivores with a low rate of sucrose assimilation was higher in Arid Monte (the most arid region) than in regions of lower aridity. Sap-feeding species could supplement their diets with sap, in varying degrees, during periods of scarcity of food resources, and White-fronted Woodpeckers through their sap wells could contribute to the persistence of this assemblage of sap-feeding bird species. Nevertheless, sap consumption by sapfeeding birds depends ultimately on the physiological and behavioral characteristics of each species.