Corvidae

The crow family, Corvidae, is a group of oscine passerine birds found across the globe. It includes crows, ravens, rooks, magpies, jackdaws, jays, treepies, choughs, and nutcrackers, with 135 species currently recognized. The genus *Corvus* alone accounts for 47 of these species, over a third of the family. The raven holds the title of the largest passerine bird. Corvids are known for their high intelligence relative to their size, ranking among the most intelligent birds studied. They have shown self-awareness in mirror tests—specifically in Eurasian magpies—and the ability to make tools, as seen in crows and rooks. These skills were long believed to belong only to humans and a few other mammals. Their brain-to-body mass ratio matches that of non-human great apes and cetaceans, falling just below that of humans.

These birds are medium to large, with strong feet and bills, rictal bristles, and they molt once a year. They live worldwide except for the southern tip of South America and the polar ice caps. Most species are found in tropical South and Central America and southern Asia, with fewer than ten species each in Africa and Australasia. The genus *Corvus* re-entered Australia in relatively recent geological prehistory, now represented by five species and one subspecies there. Several raven species have colonized oceanic islands, and some of these are now highly threatened or already extinct.

The family name Corvidae was introduced by English zoologist William Elford Leach in an 1820 guide to the British Museum. The evolutionary relationships of corvids have long been debated. They are thought to have originated from Australasian ancestors and spread worldwide from there. Other lineages from these ancestors evolved into ecologically diverse groups, often still in Australasia. In the late 1970s and 1980s, Sibley and Ahlquist grouped corvids with other taxa in the Corvida based on DNA–DNA hybridization, including currawongs, birds of paradise, whipbirds, and others. Current research, however, suggests this grouping is partly artificial. Corvids are now considered the core of the Corvoidea, alongside their closest relatives: birds of paradise, Australian mud-nesters, and shrikes. They also form the core of the Corvida, which includes groups like Old World orioles and vireos.

Cladistic analysis of DNA sequences has clarified corvid interrelationships. Jays and magpies do not form monophyletic lineages; instead, they split into American and Old World lineages, and Holarctic and Oriental lineages, which are not closely related. The position of the azure-winged magpie remains unclear. The crested jayshrike (*Platylophus galericulatus*) was traditionally placed in Corvidae but is actually closer to helmetshrikes or shrikes. Similarly, Hume's ground "jay" (*Pseudopodoces humilis*) belongs to the tit family, Paridae. A 2023 molecular study by Jenna McCullough and collaborators provides a current phylogeny of the crow family.

The earliest corvid fossils come from mid-Miocene Europe, about 17 million years ago. *Miocorvus* and *Miopica* may be ancestral to crows and some magpies, or similar due to convergent evolution. Known prehistoric corvid genera mainly belong to New World and Old World jay and Holarctic magpie lineages. These include *Miocorvus* (Middle Miocene, France), *Miopica* (Middle Miocene, Ukraine), *Miocitta* (Late Miocene, US), an indeterminate genus from the Early Pliocene of Kansas, *Protocitta* (Early Pleistocene, US), another indeterminate genus from the Early/Middle Pleistocene of Sicily, and *Henocitta* (Middle Pleistocene, US). Numerous fossil species of extant genera, mostly European *Corvus*, date from the Mio–Pliocene onward.

Corvids are large to very large passerines with a robust build and strong legs. All species except the pinyon jay have nostrils covered by bristle-like feathers. Many temperate-zone corvids have mainly black or blue plumage, though some are pied black and white, some show blue-purple iridescence, and many tropical species are brightly colored. The sexes are similar in color and size. They have strong, stout bills and large wingspans. The smallest corvid is the dwarf jay (*Cyanolyca nanus*), weighing 41 grams and measuring 21.5 cm. The largest are the common raven (*Corvus corax*) and the thick-billed raven (*Corvus crassirostris*), both regularly exceeding 1,400 grams and 65 cm. Species can be identified by size, shape, and geography.

Corvids inhabit most climatic zones. Most are sedentary and do not migrate significantly, though food shortages can trigger irruptive migration. Migratory species form large flocks in fall and travel south. One reason crows are more successful than ravens is their ability to overlap breeding territories.