135. The relationships among taxa included in
Xiphorhynchus susurrans and
X. guttatus are complex and need much additional work.
Xiphorhynchus susurrans was formerly (e.g., Zimmer 1934d, Phelps & Phelps 1950a, Peters 1951, Meyer de Schauensee 1970) considered conspecific with
X. guttatus, but Willis (1983) provided evidence that it should be treated as a separate species; this treatment was followed by Ridgely & Tudor (1994) and AOU (1998); they constitute a superspecies.
Xiphorhynchus susurrans had previously been treated as a species by Cory & Hellmayr (1925), who also treated the subspecies
polystictus (=
sororius) as a separate species; this was considered conspecific with
X. guttatus by Zimmer (1934d) and Peters (1951). However,
Aleixo (2002) found that treating
X. susurrans at the species level makes
Xiphorhynchus guttatus paraphyletic with respect to Amazonian
guttatoides group of western and southwestern Amazonia (
guttatoides, dorbignyianus, eytoni, and
vicinalis) and eastern Amazonian
guttatus group (
guttatus, polystictus, and provisionally,
connectens). Marantz et al. (2003) also emphasized that the current assignment of subspecies to either
X. susurrans or
X. guttatus does not correspond to the boundaries in vocalizations. Furthermore, the
eytoni subspecies group was formerly (e.g., Todd 1948, Meyer de Schauensee 1966, 1970) considered a separate species ("Dusky-billed Woodcreeper") from
X. guttatus; here it is treated as subspecies of
guttatus following Cory & Hellmayr (1925), Zimmer (1934d), Pinto (1937), Peters (1951), and Ridgely & Tudor (1994), but Marantz et al. (2003) noted that this group differed in vocalizations from other taxa included in
X. guttatus.
Derryberry et al. (2011) found that
eytoni was the sister to
X. guttatus +
X. susurrans.
Proposal needed to merge all three into guttatus or recognize eytoni as a species.
