Systematics

Setopagis parvula is monotypic.

Described as Caprimulgus parvulus Gould 1837; no type locality specified, "but type [is] from near Santa Fé, Rio Paraná, Argentina" (Peters 1940: 202).

Peters (1940), Meyer de Schauensee (1966), and other authors treated as parvula as polytpic, and included Nyctidromus anthonyi (Scrub Nightjar) and Setopagis heterura (Todd's Nightjar) as subspecies of parvula. Schwartz (1968) noted the considerable differences in plumage between parvula and anthonyi, and suggested that anthonyi was better classified as a species. This suggestion was confirmed when it was discovered that there were major differences in song between parvula and anthonyi (Robbins et al. 1994); the song of anthonyi is a short treeow, very different from the gurgling song of parvula. Phylogenetic analysis of DNA sequence data (from both mitochondrial and nuclear genes) confirms that anthonyi and parvula are distinct species, belonging to different clades within New World nightjars (Han et al. 2011, Sigurdsson and Cracraft 2014. The population of northern Colombia and Venezuela, heterura, is more similar in plumage to parvula (Cleere 1998), but differs vocally; the song of heterura is described as "a few short notes followed by a fast, bubbly roll, pík-you gobble-gobble-gobble" (Hilty 2003). Davis (1978) may have been the first to point out the vocal distinctions between parvula and heterura, and to recommend that heterura be recognized as a separate species.; this now is widely accepted (e.g. Dickinson and Remsen 2013).

For much of the 20th century, parvula was classified in the genus Caprimulgus, a genus that eventually encompassed a large number of species of nightjars worldwide (Salvin and Hartert 1892, Peters 1940, Dickinson 2003). Recent phylogenetic analysis of DNA sequence data, from both mitochondrial and nuclear genes, however, reveals that the broadly defined Caprimulgus of Peters (1940) and other authors is highly polyphyletic (Han et al. 2010, Sigurdsson and Cracraft 2014). Caprimulgus proper is entirely confined to the Old World, and New World species of "Caprimulgus" are split into several clades. Currently parvula is classified in the genus Setopagis, although an alternative it in an expanded Hydropsalis (Sigurdsson and Cracraft 2014). The sister species to parvula is heterura (Sigurdsson and Cracraft 2014).