General Crow/Raven Info
Classification: Crows and raves belong to the order Passerformes which include finches, warblers, woodpeckers, shrikes, vireos, and many others. Their family is Corvidae, or commonly known as the "crow family," and are of the Genus Corvus.
Scientific Nomenclature: Raven, Corvus corax, and crow, Corvus brachyrhynchos.
Sex differentiation: The sex of a raven or crow can't be determined from external appearances.
Range:Crows and ravens have ranges varying from just a few miles, as may be the case with some urban crows, upwards of hundreds of miles for some ravens.
- Corvids generally, are top of the line in avian evolution, and have made every country in the world part of their territory save New Zealand.
- The raven and crow are circumpolar--found from the Arctic Circle to the mountains of Central America. They have the flexibility and adaptive skills to thrive in the Tundra, arctic ice, in dense forest, in deserts, or amongst the urban/suburban sprawl.
Diet: Bernd Heinrich noted that many birds are evolutionary programmed to feed on one specific type of resource, for example: The phoebe sits on a perch and catches only insects that fly--the red-eyed virep looks for caterpillars under leaves of deciduous trees--the towee turns over dead leaves to find insects, ad infinitum. But crows and raven, as Lorenz (1970) noted, are "specialists in non-specialization." They love carrion, but eat anything under the sun it seems including shellfish, amphibians, louse from bovines, spiders, acorns, fish, and
- Ravens look for previous signals that meant food/rewards. Heinrich notes an anecdote about climbers on Denali getting their food swiped by ravens digging-up marked food caches in areas of up to three feet of snow.
- A general trait for most in Corvidae, is to cache excess food--but what is remarkable about this is their ability to find these exact locations despite a time lapse and subtle changes which occur in an area.
- Stealing from other birds is a well-developed component of the crows' repertoire. Kilham often observed crows robbing Great Egrets and White Ibis of their large fresh salamander catches. After the waterfowl beat the prey and dropped it, a crow would swoop in and steal it. Sometimes they would chase the Egrets and Ibis until they dropped their food, often working in a seemingly cooperative manner.
- They steal from larger birds by sneaking-up from behind, pulling some tail feather, and when the bird turns, others swoop in to nab the prize. Turkey vultures, hawks and eagles have all been victims to this tactic.
- Crows and ravens amazingly don't usually fight over food (a raven may even "recruit" others). While a crow may chase another with a mouth full, it is usually a half-hearted effort and short lived. Kilham noticed that amongst cooperative feeding groups, never did crows fight over food that a single corw had caught. This respect for individual rights extended to all despite relative social standing withing the group.
- However, crows and ravens are very territorial. Members of competing groups would be met with aggression in attempts to obtain a food source in the resident group's territory.
- Exemplifying a crows versatility and ability to cooperate, Kilham witnessed two breeding adults and a few of the yearlings attack a fawn that was visibly weak in the legs attempting to cross a pasture. One of the adults attached itself to the back of the fawn while the others attacked. After repeated falls to the ground and retaining it's feet, finally the fawn's legs could not get up one final time.
Enemies: Probably all birds that are predatory in nature are enemies to crows and ravens. These include eagles, hawks and falcons, but it is the owl that is of the highest concern. Crows and ravens will drive off these types of birds by utilizing their numbers, making lots of noise, and performing dive-bombs towards the enemy while chasing it out of their territory. At night though, the crow is most vulnerable. Roosting in large numbers, owls, with their stealth-like hunting skills can make easy prey. Ravens, the more solitary of the two, are less at risk.
Ecological Benefits: Despite a duly reputation as crop stealers and dumpster divers, a study found that a family of crows devoured about forty thousnd grubs, caterpillars, army worms and other pests to farmers in just one nesting period. Also, they aid in keeping rodent populations down, and on a dubious note, help to keep our streets free of road-kill remains.
Vocaliziations: Crows and ravens have a variety of calls they use. Crows exhibit at least two dozen different calls, and ravens express themselves with 20-100's depending on the "expert" one refers. Calls that may mean "warning," "food here," but also probably used to identify themselves to a certain group. When Kilham was attempting to wean his pet raven from a domestic life, he noticed that a juvenile raven flew abouve making "quaaas", and his raven responded similarly, like it was in conversation. Then on another occasion, an adult flew over making harsh "kwacks", sending the pet raven straight to his shoulder scared. Specific vocalizations may be used in times of intimate gesturing also. Kilham noted during one of his intimate sessions with his pet raven, a soft, low "er-uk" that he never heard again.
Courtship and "family life": Crows and ravens mate for life, but will quickly find a mate in the other dies.
- Crows and ravens, like most Corvids, share the responsibility of nest building.
- It appears that ravens, and possibly crows, hide any surplus food. This may be done to keep the necessary foraging distance to a minimum, especially when there is young at the nest vulnerable to predation.
- Both male and female will help rear the young (even some auxiliaries!)--crows and ravens are good parents also-- providing for the young longer than any other bird and will often leave the nest to the young.
- Chicks in a brood appear to be fed by which gape is stretched the highest and that which maintains the loudest squawks. Apparently, there is anonymity in regards to the relationship between chicks and the parents. Savage (1995) notes that chicks moved from brood to brood were still fed by parents of the nest, suggesting that it is their nest contents that is of concern and not any individualy chick attachments.
However, it has been noted that chicks may acquire vocalizations that provide identity to fledglings even after months of separation.
Cooperation: The Corvids, in general, are considered to be a social group. It seems that it is a combination of factors that keep social families of various species together--probably a combination of vocaliziation recognition; behavior; and physical appearance.
Native names: Ravens, Corvus corax, are also known as Yel, Txamsem, Hemaskus, and Tsesketco by Pacific Northwest Native American tribes.
- One advantage of living in social societies may be that each individual has the potential of becoming privy to a new food source to share with the rest of the clan, and furthermore by observing associates one can copy those skillful in discovering food sources.
- Ravens, and especially crows, will work together in foraging. For example, they may team-up to distract turkey vultures or eagles while another swipes away the food; or they may provoke mating pairs to leave their nest, thus leaving it's contents vulnerable to predation.