The Common Raven (Corvus corax), also known as the Northern Raven, is a large all-black passerine bir in the crow family. Found across the northern hemisphere, it is the most widely distributed of all corvids. There are eight known subspecies with little variation in appearance, although recent research has demonstrated significant genetic differences among populations from various regions. It is one of the two largest corvids, alongside the Thick-billed Raven, and is possibly the heaviest passerine bird; at maturity, the Common Raven is between 56 and 69 cm (22 to 27 inches) in length, with recorded weights ranging from 0.69 to 1.63 kg (1.5 to 3.6 pounds). Common Ravens typically live about 10 to 15 years in the wild, although lifespans of up to 40 years have been recorded. Young birds may travel in flocks, but later mate for life, with each mated pair defending a territory.