Red-naped and Red-breasted Sapsuckers, together with the Yellow-bellied Sapsucker (Sphyrapicus varius), form a superspecies. These 3 species have, for the most part, separate distributions but were long treated as forms of a single species – the “Yellow-bellied Sapsucker” – until 1983, when systematic studies showed distinctions sufficient to warrant taxonomic treatment as separate species. The biology of these 3 species appears to be quite similar.
The name “sapsucker” has been applied to the woodpecker genus Sphyrapicus because these birds create sap wells in the bark of woody plants and feed on sap that appears there. Sap wells are shallow holes drilled through outer bark to the underlying phloem or xylem tissues. When Red-naped Sapsuckers first arrive at their breeding areas, they often drill sap wells in the xylem of conifers and quaking aspen (Populus tremuloides). Once temperatures increase and sap begins to flow, these birds switch to phloem wells in aspen or willow (Salix spp.), if available. Sapsuckers create elaborate systems of sap wells and maintain this resource throughout the day to ensure sap production. Because of this large investment in maintenance, sapsuckers defend wells from other sapsuckers, as well as from other species. When feeding young, sapsuckers usually forage for arthropods – especially ants (Formicidae) – and some of these prey items are dipped in sap wells, perhaps for added nutritional value.