Owlet-nightjars areinsectivores which hunt mostly in the air but sometimes on the ground; their soft plumage is a cryptic mixture of browns and paler shades, they have fairly small, weak feet (but larger and stronger than those of a frogmouth or a nightjar), a tiny bill that opens extraordinarily wide, surrounded by prominent whiskers. The wings are short, with 10 primaries and about 11 secondaries; the tail long and rounded.
The genusAegotheles was introduced in 1827 by the naturalistsNicholas Vigors andThomas Horsfield to accommodate a single species,Caprimulgus novaehollandiaeLatham, 1790.[2][3] This binomial name is considered to be ajunior synonym ofCaprimulgus cristatus, theAustralian owlet-nightjar that was introduced byGeorge Shaw earlier in 1790.[4][5][6] The genus name means "nightjar" or "goatsucker" fromAncient Greek αιξ/aix, αιγος/aigos meaning "goat" and θηλαζω/thēlazō meaning "to suckle".[7] The family Aegothelidae was introduced (as subfamily Aegothelinae within the familyCaprimulgidae) in 1853 by the French naturalistCharles Lucien Bonaparte.[8][9]
A comprehensive 2003 study analyzingmtDNAsequences ofCytochrome b andATPase subunit 8 suggests that 12 living species of owlet-nightjar should be recognized, as well as another that became extinct early in thesecond millennium AD.[10]
The relationship between the owlet-nightjars and the (traditional)Caprimulgiformes has long been controversial and obscure and remains so today: in the 19th century they were regarded as a subfamily of thefrogmouths, and they are still generally considered to be related to the frogmouths and/or thenightjars. It appears though that they are not as closely related to either as previously thought, and that the owlet-nightjars share a more recent common ancestor with theApodiformes.[11] As has been suggested on occasion sincemorphological studies of thecranium in the 1960s,[12] they are thus considered a distinctorder,Aegotheliformes. This, the caprimulgiform lineage(s), and the Apodiformes, are postulated to form aclade calledCypselomorphae, with the owlet-nightjars and the Apodiformes forming the cladeDaedalornithes.
In form and habits, however, they are very similar to both caprimulgiform group – or, at first glance, to smallowls with huge eyes. The ancestors of theswifts andhummingbirds, two groups of birds which are morphologically very specialized, seem to have looked very similar to a small owlet-nightjar, possessing strong legs and a wide gape, while the legs and feet are very reduced in today's swifts and hummingbirds, and the bill is narrow in the latter.
Owlet-nightjars are an exclusively Australasian group, but close relatives apparently thrived all overEurasia in the latePaleogene.
Molecular phylogenetic studies have shown the Aegotheliformes aresister to theApodiformes containing the hummingbirds, swifts and treeswifts.[13][14] The two orders shared a common ancestor around 57 million years ago.[14]
The followingcladogram is based on a 2003molecular phylogenetic study that sampled three regions of mitochondrial DNA mainly extracted from museum specimens. Some of the nodes were not well supported by the data.[10]
^abDumbacher, J.P.; Pratt, T.K.; Fleischer, R.C. (2003). "Phylogeny of the owlet-nightjars (Aves: Aegothelidae) based on mitochondrial DNA sequence".Molecular Phylogenetics and Evolution.29 (3):540–549.Bibcode:2003MolPE..29..540D.doi:10.1016/S1055-7903(03)00135-0.
^Prum, Richard O.; Berv, Jacob S.; Dornberg, Alex; Field, Daniel J.; Townsend, Jeffrey P.; Lemmon, Emily Moriarty; Lemmon, Alan R. (2015). "A comprehensive phylogeny of birds (Aves) using targeted next-generation DNA sequencing".Nature.526 (7574):569–573.Bibcode:2015Natur.526..569P.doi:10.1038/nature15697.PMID26444237.S2CID205246158.
Simonetta, A.M. (1967): Cinesi e morfologia del cranio negli Uccelli non passeriformi. Studio su varie tendenze evolutive. Part II – Striges, Caprimulgiformes ed Apodiformes ["Cranial kinesis and morphology of non-passerine birds. Study of various evolutionary tendencies. Part II – Striges, Caprimulgiformes and Apodiformes"]. [In Italian[verification needed]]Archivio Zoologico Italiano52: 1–35.
