Other adaptations shared by both Old and New World vultures include a bald head, devoid of feathers which prevents rotting matter from accumulating while feeding, and an extremely disease-resistant digestive system to protect against scavenging-related germs.

The family Cathartidae was introduced (as the subfamily Cathartinae) by the French ornithologist Frédéric de Lafresnaye in 1839.

[7] However, in the late 20th century some ornithologists argued that they are more closely related to storks on the basis of karyotype,[8] morphological,[9] and behavioral[10] data.

This was criticized,[11][12] and an early DNA sequence study[13] was based on erroneous data and subsequently retracted.

[14][15][16] There was then an attempt to raise the New World vultures to the rank of an independent order, Cathartiformes, not closely associated with either the birds of prey or the storks and herons.

[18] The fossil history of the Cathartidae is complex, and many taxa that may possibly have been New World vultures have at some stage been treated as early representatives of the family.

Extinct taxa include: New World vultures are generally large, ranging in length from the lesser yellow-headed vulture at 56–61 centimeters (22–24 inches) up to the California and Andean condors, both of which can reach 120 centimeters (48 inches) in length and weigh 12 or more kilograms (26 or more pounds).

[7] New World vultures are restricted to the western hemisphere, ranging from southern Canada to South America.

These species of birds are also occasionally seen in human settlements, perhaps emerging to feed upon the food sources provided from roadkills.

[citation needed] New World vultures and condors do not build nests, but lay eggs on bare surfaces.

The genus Cathartes locates carrion by detecting the scent of ethyl mercaptan, a gas produced by the bodies of decaying animals.

[40] Vultures possess a very acidic digestive system, with their gut dominated by two species of anaerobic bacteria that help them withstand toxins present in decaying prey.

[50] In a 2014 study of 50 (turkey and black) vultures, researchers analyzed the microbial community or microbiome of the facial skin and the large intestine.

Two anaerobic faecal bacteria groups that are pathogenic in other vertebrates stood out: Clostridia and Fusobacteriota (formerly Fusobacteria).

Unexpectedly, both groups of anaerobic bacteria were also found on the air-exposed facial skin samples, with Clostridia at 7%–40% and Fusobacteriota up to 23%.

Genes that encode tissue-degrading enzymes and toxins that are associated with Clostridium perfringens have been found in the vulture gut metagenome.

[55] Meanwhile, the American black vulture is normally connected with death or shown as a bird of prey, and its glyph is often depicted attacking humans.