Strisores (/straɪˈsoʊriːz/ stry-SOH-reez[3]), sometimes called nightbirds, is a clade of birds that includes the living families and orders Caprimulgidae (nightjars, nighthawks and allies), Nyctibiidae (potoos), Steatornithidae (oilbirds), Podargidae (frogmouths), Apodiformes (swifts and hummingbirds), as well as the Aegotheliformes (owlet-nightjars) whose distinctness was only recently realized.

The synapomorphies that define this clade are the ossa maxillaria separated by a large cleft, a mandible with short pars symphysialis, and rami mandibulae slender in their distal half.

Jean Cabanis originally coined the name Strisores in 1847 as an order encompassing a much broader group of birds subdivided into two 'tribes': the Macrochires (hummingbirds, swifts, and nightjars, including oilbirds and potoos, but notably excluding frogmouths) and the Amphibolae (hoatzin, mousebirds, and turacos).

[8] In 1867, Thomas Henry Huxley proposed the name Cypselomorphae for hummingbirds, swifts, and nightjars (including owlet-nightjars and potoos), however, he considered frogmouths and oilbirds unrelated due to aspects of their skull morphology.

[16][17] The discovery has led to a challenge of reconciling a Linnean hierarchy with phylogenetic relationships while still maintaining nomenclatural stability, resulting in a complicated situation where some researchers currently use the resurrected name Strisores in a new sense,[17][18] others expand the order Caprimulgiformes to include the 'traditional' apodiform families,[19] whereas others[20] use the superordinal name Caprimulgimorphae Cracraft, 2013,[21] raising the 'traditional' caprimulgiform families to the rank of order.

In addition, Eocypselus, a Late Paleocene or Early Eocene genus of North America, cannot be assigned to any one strisore lineage with certainty but appears to be some ancestral form.

By the distribution of fossils, the Paleogene radiation seems to have originated in Asia, which at that time became a highly fragmented landscape as the Himalayas lifted up and the Turgai Strait started to disappear.

Several fossil taxa are tentatively placed here as basal or incertae sedis Strisores contains the extant orders Aegotheliformes, Apodiformes (with families Apodidae, Hemiprocnidae, and Trochilidae), Caprimulgiformes, Nyctibiiformes, Podargiformes, Steatornithiformes.

Based on analysis of DNA sequence data – notably β-fibrinogen intron 7 – Fain and Houde considered the families of the Caprimulgiformes to be members of the proposed clade Metaves, which also includes the hoatzin, tropicbirds, sandgrouse, pigeons, kagu, sunbittern, mesites, flamingos, grebes and swifts and hummingbirds.

No morphological synapomorphies have been found that uniquely unite Metaves (or Caprimulgiformes for that matter), but numerous unlinked nuclear genes independently support their monophyly either in majority or whole.

Initial mtDNA cytochrome b sequence analysis agreed with earlier morphological and DNA-DNA hybridization studies insofar as that the oilbird and the frogmouths seemed rather distinct.

It robustly supported, however, the idea that the owlet-nightjars should be considered closer to Caprimulgiformes, unlike the methodologically weaker studies of Mariaux & Braun (1996) and Fain and Houde (2004).

[35] Caprimulgidae (nightjars) Steatornithidae (oilbird) Nyctibiidae (potoos) Podargidae (frogmouths) Aegothelidae (owlet-nightjars) Trochilidae (hummingbirds) Apodidae (swifts) Hemiprocnidae (treeswifts)