Corvidae

Corvidae is a cosmopolitan family of oscine passerine birds that contains the crows, ravens, rooks, jackdaws, jays, magpies, treepies, choughs, and nutcrackers. In common English, they are known as the crow family, or, more technically, corvids. Over 120 species are described. The genus Corvus, including the jackdaws, crows, rooks, and ravens, makes up over a third of the entire family. Corvids display remarkable intelligence for animals of their size and are among the most intelligent birds thus far studied. Specifically, members of the family have demonstrated self-awareness in mirror tests (European magpies) and tool-making ability (e.g., crows and rooks), skills which until recently were thought to be possessed only by humans and a few other higher mammals. Their total brain-to-body mass ratio is equal to that of non-human great apes and cetaceans, and only slightly lower than that of humans. They are medium to large in size, with strong feet and bills, rictal bristles, and a single moult each year (most passerines moult twice). Corvids are found worldwide except for the tip of South America and the polar ice caps. The majority of the species are found in tropical South and Central America, southern Asia and Eurasia, with fewer than 10 species each in Africa and Australasia. The genus Corvus has re-entered Australia in relatively recent geological prehistory, with five species and one subspecies there. Several species of raven have reached oceanic islands, and some of these species are now highly threatened with extinction or have already become extinct. The family Corvidae was introduced by the English zoologist William Elford Leach in a guide to the contents of the British Museum published in 1820. Over the years, much disagreement has arisen on the exact evolutionary relationships of the corvid family and their relatives. What eventually seemed clear was that corvids are derived from Australasian ancestors and from there spread throughout the world. Other lineages derived from these ancestors evolved into ecologically diverse, but often Australasian groups. In the late 1970s and throughout the 1980s, Sibley and Ahlquist united the corvids with other taxa in the Corvida, based on DNA–DNA hybridization. The presumed corvid relatives included currawongs, birds of paradise, whipbirds, quail-thrushes, whistlers, monarch flycatchers and drongos, shrikes, vireos, and vangas, but current research favors the theory that this grouping is partly artificial. The corvids constitute the core group of the Corvoidea, together with their closest relatives (the birds of paradise, Australian mud-nesters, and shrikes). They are also the core group of the Corvida, which includes the related groups, such as Old World orioles and vireos. Clarification of the interrelationships of the corvids has been achieved based on cladistic analysis of several DNA sequences. The jays and magpies do not constitute monophyletic lineages, but rather seem to split up into an American and Old World lineage, and an Holarctic and Oriental lineage, respectively. These are not closely related among each other. The position of the azure-winged magpie, which has always been a major enigma, is even less clear than before. The crested jay (Platylophus galericulatus) is traditionally included in the Corvidae, but might not be a true member of this family, possibly being closer to the helmetshrikes (Malaconotidae) or shrikes (Laniidae); it is best considered Corvidae incertae sedis for the time being. Likewise, the Hume's ground 'jay' (Pseudopodoces humilis) is in fact a member of the tit family Paridae. The following tree represents current insights in the phylogeny of the Crow family according to J. Boyd. The earliest corvid fossils date to the mid-Miocene, about 17 million years ago; Miocorvus and Miopica may be ancestral to crows and some of the magpie lineage, respectively, or similar to the living forms due to convergent evolution. The known prehistoric corvid genera appear to be mainly of the New World and Old World jay and Holarctic magpie lineages: In addition, there are numerous fossil species of extant genera since the Mio–Pliocene, mainly European Corvus.