There are three recognized subspecies of Ramphastos ambiguus, which are not believed to overlap in geographic distribution. These differ solely in soft part color; as Short and Horne (2001: 249) note, "Differences between subspecies are very small, involving bill color features that are not absolute, nor is the color of orbital skin likely to be of much importance".
swainsonii, described as Rhamphastos Swainsonii Gould 1833; type locality "Mountains of Colombia"
Occurs from southeastern Honduras to western Colombia (east to the Cauca Valley) and western Ecuador. Differs from nominate ambiguus in bill color (see Bare Parts).
abbreviatus, described as Ramphastos abbreviatus Cabanis 1862; type locality Puerto Cabello, Venezuela
Occurs in northeastern Colombia (west slope of the Eastern Andes south to the central Magdalena Valley) and northwestern and northern Venezuela
Averages slightly smaller than ambiguus, and has yellow green, not blue, orbital skin.
ambiguus, described as Ramphastos ambiguus Swainson 1823; type locality not designated, restricted by Chapman (1917: 328) to Buenavista, Colombia
Occurs along the eastern Andes from southern Colombia (upper Magdalena Valley) to central Peru.
See Detailed Description.
Ramphastos ambiguus is one of 7 to 15 species level taxa in the genus Ramphastos (de Germiny 1929, Peters 1948, Meyer de Schauensee 1966, 1970, Haffer 1974, Short and Horne 2001, 2002). Among the Ramphastos toucans, there are two sister clades, as suggested by Haffer (1974) and later supported by DNA evidence (Weckstein 2005, Patané et al. 2009). One subgenus-level clade, known as the "smooth-billed yelpers", includes R. ambiguus, and White-throated Toucan (R. tucanus). The other group, known as the "channel-keel-billed croakers", includes Keel-billed Toucan (R. sulfuratus), Choco Toucan (R. brevis), and several other species that make croaking vocalizations.
Haffer (1974) noted that "nowhere in the neotropical forests live more than two species of Ramphastos in the same area. When they do, one is usually a representative of the channel-keel-billed [croakers] and the other a member of the smooth-billed [yelpers]". Indeed, Yellow-throated Toucan follows this rule, occurring sympatrically with Keel-billed and Choco toucans but not with other smooth-billed taxa.
There has been ongoing debate as to whether "Chestnut-mandibled" (swainsonii) and "Black-mandibled" (nominate ambiguus, abbreviatus) toucans should be considered conspecific. The ranges of these two groups do not seem to come into contact except in the central Magdalena valley of Colombia, and even here, the extent of overlap is undetermined (Hilty and Brown 1986). Weckstein (2005) found that swainsonii and ambiguus are 1.35% divergent in mitochondrial DNA. As a further complication, the geographically intermediate subspecies of abbreviatus usually is considered to be more closely related to ambiguus, but some authors (Stiles et al. 1999) place it closer to swainsonii based on geographic proximity and orbital skin color. Whether abbreviatus is closer to swainsonii, ambiguus, or is a "stable hybrid" population is unknown. More research needs to be done -particularly in the Magdalena Valley- to determine taxonomic limits within this complex.