Red-naped, Red-breasted (Sphyrapicus ruber), and Yellow-bellied Sapsucker (S. 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. Most of the early literature and research on this complex refer to Yellow-bellied Sapsuckers of eastern North America (found generally east of the Rocky Mountains). Limited, but more recent, work has focused on populations of the Red-naped Sapsucker of the Rocky Mountain trench region from central British Columbia to Arizona. 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. This species creates elaborate systems of sap wells and maintains 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.
Other species make use of sapsucker wells to supplement their food intake with sap or with insects attracted to the sap. Rufous Hummingbirds (Selasphorus rufus), for example, appear to be closely associated, ecologically, with Red-naped Sapsuckers and they place their nests near sap wells, follow sapsuckers in their daily movements, and may even time their migration to coincide with that of sapsuckers so they can feed off the sap wells. In addition, sapsuckers excavate nest cavities that often provide nesting or roost sites for other species of birds (for example, Mountain Bluebirds [Sialia currucoides]), and even some mammals (for example, northern flying squirrel [Glaucomys sabrinus]) that cannot excavate their own.
In areas where their ranges overlap, Red-breasted and Red-naped sapsuckers are known to hybridize. The first major study of the breeding biology of these species was by Thomas Howell, who conducted 163 hours of observations at 14 nests in a hybrid zone in Modoc County, California ( Howell 1952 ). Most recent work on this species has focused on Red-breasted–Red-naped sapsucker hybrid zones in Oregon ( Trombino 1998 ) and on the breeding biology of Red-naped Sapsuckers in Nevada ( Fleury 2000 ) and British Columbia ( Walters 1996 ). Reference to, and comparisons with, Yellow-bellied Sapsucker studies aid our understanding of this species (see Walters et al. 2002c ).