Corvidae – Crows, Jays, Magpies & Allies

The Corvidae (Crows, Jays, Magpies and allies) also known as the corvids or simply the crow family, are a fascinating family of birds. The corvids happen to be one of the larger bird families with around 135 species. Many people do not know the crow family includes a variety of birds other than the crows and ravens including the jays, rooks, treepies, magpies, choughs (pronounced ‘chuffs’), jackdaws and nutcrackers.  The genus Corvus containing 50 species makes up over a third of the entire family. Many species are among the largest passerines and the raven species are the largest of all. The variation within this family is abundant. The similarities are as well.

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 spread throughout the world from there. Other lineages derived from these ancestors evolved into ecologically diverse, but often Australasian, groups. 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 a Holarctic and Oriental lineage, respectively. These are not closely related among each other. The position of the azure-winged magpie, which has always been of undistinguished lineage, is less clear than previously thought.

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 corvids of temperate zones have mainly black or blue coloured plumage; however, some are pied black and white, some have a blue-purple iridescence, and many tropical species are brightly coloured. The sexes are very similar in colour and size. Corvids have strong, stout bills and large wingspans. The smallest corvid is the Dwarf Jay Cyanolyca nanus, at 41 g and 21.5 cm. The largest corvids are the Common Raven Corvus corax and the Thick-billed Raven Corvus crassirostris, both of which regularly exceed 1,400 grams and 65 cm. Species can be identified based on size, shape, and geography; however, some, especially the Australian crows, are best identified by their raucous calls.

All 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 southern tip of South America and the polar ice caps. The majority of the species are found in tropical South and Central America and in southern Asia, 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. Corvids occur in most climatic zones. Most are sedentary, and do not migrate significantly. However, during a shortage of food, irruptive migration can occur. When species are migratory, they will form large flocks in the early autumn (around August in the Northern Hemisphere) and travel south.

Many species are territorial, protecting territories throughout the year, or simply during the breeding season. In some cases, territories may only be guarded during the day, with the pair joining off-territory roosts at night. Some corvids are well-known communal roosters. Some groups of roosting corvids can be very large, with a roost of 65,000 rooks once counted in Scotland. Some, including the rook and the jackdaw, are also communal nesters.

Some corvids have strong organization and community groups. Jackdaws, for example, have a strong social hierarchy, and are facultatively colonial during breeding. Providing mutual aid has also been recorded within many of the corvid species.

Some corvids can be aggressive. Blue jays, for example, are well known to attack anything that threatens their nest. Crows have been known to attack dogs, cats, ravens, and birds of prey. Most of the time, these assaults take place as a distraction long enough to allow an opportunity for stealing food.

The natural diet of many corvid species is omnivorous, consisting of invertebrates, nestlings, small mammals, berries, fruits, seeds, and carrion. However, some corvids, especially the crows, have adapted well to human conditions, and have come to rely on human food sources. In a US study of American Crows, Common Ravens, and Steller’s Jays around campgrounds and human settlements, the crows appeared to have the most diverse diet of all, taking anthropogenic foods, such as: bread, spaghetti, fried potatoes, dog food, sandwiches, and livestock feed. The increase in available human food sources is contributing to population rises in some corvid species.

Some corvids are predators of other birds. During the wintering months, corvids typically form foraging flocks. However, some crows also eat many agricultural pests, including cutworms, wireworms, grasshoppers, and harmful weeds. Some corvids will eat carrion, and since they lack a specialized beak for tearing into flesh, they must wait until animals are opened, whether by other predators or as roadkill.

Pied Crow Corvus albus

Yellow-billed Magpie Pica nuttalli

Mate selection is quite complex, and accompanied with much social play in the Corvidae. Youngsters of social corvid species undergo a series of tests, including aerobatic feats, before being accepted as a mate by the opposite sex. The partner bonds are extremely strong, and even lifelong in some species. This monogamous lifestyle, however, can still contain extra-pair copulations. Males and females build large nests together in trees or on ledges; jackdaws are known to breed in buildings and in rabbit warrens. The male will also feed the female during incubation. The nests are constructed of a mass of bulky twigs lined with grass and bark. Corvids can lay between three and ten eggs, typically ranging between four and seven. The eggs are usually greenish in colour with brown blotches. Once hatched, the young remain in the nests for up to 6–10 weeks depending on the species.

Florida Scrub Jay Aphelocoma coerulescens	Brown Jay Cyanocorax morio
White-throated Jay Cyanolyca mirabilis	Unicolored Jay Aphelocoma unicolor

Corvids use several different forms of parental care, including bi-parental care and cooperative breeding. Helpers at the nest in most cooperatively-breeding birds are males, while females join other groups. White-throated Magpie-jays are cooperatively-breeding corvids where the helpers are mostly female. Young corvids have been known to play and take part in elaborate social games. Documented group games follow ‘king of the mountain’ or ‘follow the leader’ patterns. Other play involves the manipulation, passing, and balancing of sticks. Corvids also take part in other activities, such as sliding down smooth surfaces. These games are understood to play a large role in the adaptive and survival ability of the birds.

Grey Jay Perisoreus canadensis

Clark’s Nutcracker Nucifraga columbiana

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 (Eurasian 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 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 the most intelligent, adaptive birds in the world. Captivating and outwardly curious they use ordinary objects as tools and toys. Wise enough to know the benefits of playing, they know how to have fun. They are some of the only birds who engage in social play like humans. They are forward thinking birds – always planning ahead, caching food up to a year and then retrieving it from hundreds of different locations with ease.