The true
crows are large
passerine birds that form the
genus Corvus in the family
Corvidae.
Ranging in size from the relatively small
pigeon-sized jackdaws
(Eurasian and Daurian) to the Common Raven of the Holarctic region and Thick-billed Raven of the highlands of
Ethiopia
, the 40 or
so members of this genus occur on all temperate continents (except South
America) and several offshore and oceanic islands (including
Hawaii
). In the United States
, the word "crow" is used to refer to the American Crow.The crow genus makes up a
third of the species in the
Corvidae
family. Other corvids include
rook and
jays. Crows appear to have evolved in Asia from
the corvid stock, which had evolved in Australia. A group of crows
is called a "murder," though this term usually appears in poetry or
similar literature rather than ordinary usage.
Systematics
The genus was originally described by
Linnaeus in his 18th century work
Systema Naturae. The name
is derived from the
Latin
corvus meaning "raven".The
type
species is the
Common Raven
(Corvus corax); others named in the same work include the
Carrion Crow (C. corone), the
Hooded Crow (C. cornix), the
Rook (C. frugilegus), and the
Jackdaw (C. monedula).
There is no good systematic approach to the genus at present.
Generally, it is assumed that the species from a geographical area
are more closely related to each other than to other lineages, but
this is not necessarily correct. For example, while the
Carrion/Collared/House Crow complex is certainly closely related to
each other, the situation is not at all clear regarding the
Australian/Melanesian species. Furthermore, as many species are
similar in appearance, determining actual range and characteristics
can be very difficult, such as in Australia where the five
(possibly six) species are almost identical in appearance.
The
fossil record of crows is rather
dense in Europe, but the relationships among most prehistoric
species is not clear. Jackdaw-, crow- and raven-sized forms seem to
have existed since long ago and crows were regularly hunted by
humans up to the
Iron Age, documenting the
evolution of the modern taxa. American crows are not as
well-documented.
A surprisingly high number of species have become
extinct after human colonization, especially of
island groups such as New Zealand, Hawaii and Greenland.
Species
Living and recently extinct species
- Species name - Common Names (range)
- Corvus alberculos - White-necked Raven or Cape Raven
(Southern, central and eastern Africa)
- Corvus albus - Pied Crow
(Central African coasts to southern Africa)
- Corvus bennetti - Little
Crow (Australia)
- Corvus brachyrhynchos - American Crow (North America, southern Canada,
northern Mexico)
- Corvus capensis - Cape Crow
or Black Crow or Cape Rook (Eastern and southern Africa)
- Corvus caurinus - Northwestern Crow (Olympic peninsula to
southwest Alaska)
- Corvus corax - Common
Raven or Northern Raven (The Holarctic south throughout middle
Europe, Asia, and North America to Nicaragua)
- Corvus (corax) sinuatus - Western Raven (Holarctic; Arctic, North
America, Eurasia, northern Africa, Pacific islands and British
Isles)
- Corvus (corax) varius morpha leucophaeus -
Pied Raven an extinct color variant
(Holarctic)
- Corvus corone - Carrion
Crow or Eurasian Crow (Western Europe from British Isles to
Germany, eastern Asia)
- Corvus (corone) capellanus - Mesopotamian Crow or Iraq Pied Crow
(Southern Iraq to extreme southwest Iran)
- Corvus (corone) cornix - Hooded
Crow (Northern and western Europe through Turkey, but only
North Western Scotland and Northern Ireland in the United Kingdom
as the Carrion Crow is more common on most of the British mainland;
Syria, Iran, Iraq)
- Corvus (corone) orientalis - Eastern Carrion Crow (Eurasia and
northern Africa)
- Corvus coronoides - Australian Raven (Eastern and southern
Australia)
- Corvus crassirostris - Thick-billed Raven (Ethiopia)
- Corvus cryptoleucus - Chihuahuan Raven (Southwestern U.S.,
northwestern Mexico)
- Corvus dauuricus - Daurian
Jackdaw (Eastern Europe to eastern Japan, occasionally
Scandinavia)
- Corvus enca - Slender-billed Crow (Malaysia, Borneo,
Indonesia)
- Corvus (enca) violaceus - Violaceous Crow
(Philippines, Ceram, Moluccas)
- Corvus florensis - Flores
Crow (Flores Island)
- Corvus frugilegus - Rook
(Europe, Asia, New Zealand)
- Corvus fuscicapillus - Brown-headed Crow (New Guinea)
- Corvus hawaiiensis (formerly C. tropicus) -
Hawaiian Crow or 'Alala (Island of
Hawaii)
- Corvus imparatus - Tamaulipas Crow (Gulf of Mexico coast from
Nuevo Leon east to Rio Grande delta, south to Tampico,
Tamaulipas)
- Corvus jamaicensis - Jamaican
Crow (Jamaica)
- Corvus kubaryi - Mariana
Crow or Aga (Guam, Rota)
- Corvus leucognaphalus - White-necked Crow (Haiti, Dominica, Puerto
Rico)
- Corvus macrorhynchos - Large-billed Crow (Eastern Asia,
Himalayas, Philippines)
- Corvus (macrorhynchos) levaillantii - Jungle Crow (India, Burma)
- Corvus meeki - Bougainville Crow or Soloman Islands Crow
(Northern Soloman Islands)
- Corvus mellori - Little
Raven (Southeastern Australia)
- Corvus monedula - Jackdaw or
Western Jackdaw (British Isles and western Europe, Scandinavia,
northern Asia, Northern Africa)
- Corvus moneduloides - New Caledonian Crow (New Caledonia,
Loyalty Islands)
- Corvus nasicus - Cuban Crow
(Cuba, Isla de la Juventud, Grand Caicos Island)
- Corvus orru - Torresian
Crow or Australian Crow (Australia, New Guinea and nearby
islands)
- Corvus ossifragus - Fish Crow
(Eastern U.S. coast, southeastern U.S. through Florida, west along
major rivers to Oklahoma and Texas)
- Corvus palmarum - Palm Crow
(Cuba, Haiti, Dominica)
- Corvus rhipidurus - Fan-tailed Raven (Northeast Africa, Middle
East)
- Corvus ruficolis - Brown-necked Raven or Desert Raven
(Northern Africa, Arabia, southeast to eastern Asia)
- Corvus (ruficolis) edithae - Somali Crow or Dwarf Raven (Northeast
Africa)
- Corvus sinaloae - Sinaloan
Crow (Pacific coast from Sonora to Colima)
- Corvus splendens - House
Crow or Indian House Crow (Indian subcontinent, Middle East,
east Africa)
- Corvus tasmanicus - Forest
Raven or Tasmanian Raven (Tasmania and adjacent south coast of
Australia)
- Corvus (tasmanicus) boreus - Relict Raven (Northeastern New South
Wales)
- Corvus torquatus - Collared
Crow (Eastern China, south into Vietnam)
- Corvus tristis - Grey Crow or
Bare-faced Crow (New Guinea and neighboring islands)
- Corvus typicus - Piping
Crow or Celebes Pied Crow (Sulawesi, Muna, Butung)
- Corvus unicolor - Banggai
Crow (Banggai Island) - possibly extinct
- Corvus validus - Long-billed Crow (Northern Moluccas)
- Corvus woodfordi - White-billed Crow or Soloman Islands Crow
(Southern Soloman Islands)
List sources
Prehistoric and fossilized species
In addition to the prehistoric forms listed above, some extinct
chronosubspecies have been described.
These are featured under the respective species accounts.
Crows and humans
Certain species have been considered pests; the
Common Raven,
Australian Raven and
Carrion Crow have all been known to kill weak
lambs as well as eating freshly dead corpses probably killed by
other means.
Rooks have been blamed for
eating grain in the UK and
Brown-necked Raven for raiding date crops
in desert countries.
In Auburn, New York (USA), 25,000 to 50,000 American Crows (C.
brachyrhynchos) have taken to roosting in the small city's large
trees during winter since around 1993. In 2003, a controversial,
organized crow hunt proved ineffective at reducing their numbers
and the problem (concerns for public health and the sheer noise of
so many crows) continues.
At a
Technology Entertainment Design
conference in March 2008,
Joshua
Klein presented the potential use of a
vending machine for crows. He suggested the
crows could be trained to pick up
trash and
the vending machine would be designed to give a reward in exchange
for the trash.
Crows have also been known to imitate the
human voice, just like
parrots. Crows that have been trained to "speak" are
considered valuable in parts of
East Asia,
as crows are a sign of luck.
Some people have adopted crows as
pets.
Though humans cannot generally tell individual crows apart, crows
have been shown to have the ability to visually recognize
individual humans, and to transmit information about "bad" humans
by squawking.
Hunting
In the United States it is legal to hunt crows in all states
usually from around August to the end of March and anytime if they
are causing a nuisance or health hazard. There is no bag limit when
taken during the "crow hunting season." According to the US
Code of Federal Regulations, crows may be taken without a
permit in certain circumstances.
USFWS 50
CFR 21.43 (Depredation order for
blackbirds, cowbirds, grackles, crows and magpies) states that a
Federal permit is not required to control these birds "when found
committing or about to commit depredations upon ornamental or shade
trees, agricultural crops, livestock, or wildlife, or when
concentrated in such numbers and manner as to constitute a health
hazard or other nuisance," provided
that none of the birds killed or their parts are sold or
offered for sale,
that anyone exercising the privileges granted by this section
shall permit any Federal or State game agent free and unrestricted
access over the premises where the operations have been or are
conducted and will provide them with whatever information required
by the officer, and
that nothing in the section authorizes the killing of such
birds contrary to any State laws and that the person needs to
possess whatever permit as may be required by the State.
In the UK,
the crow is considered a pest when in a large community and under
certain conditions can be shot under a number of general licenses
issued by DEFRA
.
Evolution
Crows appear to have
evolved in central
Asia and radiated out into
North America,
Africa,
Europe, and
Australia.
The latest evidence in the crow's evolution indicates descent from
the Australasian family Corvidae. However, the branch that would
produce the modern groups such as
jays,
magpies and large predominantly black
Corvus had left
Australasia and
were concentrated in
Asia by the time the
Corvus evolved.
Corvus has since re-entered Australia
(relatively recently) and produced five species with one recognized
sub-species.
Behavior
Calls
Crows make a wide variety of calls or vocalizations. Whether the
crows' system of communication constitutes a
language is a topic of debate and study. Crows have
also been observed to respond to calls of other species; this
behavior is presumably learned because it varies regionally. Crows'
vocalizations are complex and poorly understood. Some of the many
vocalizations that crows make are a "caw", usually echoed back and
forth between birds, a series of "caws" in discrete units, counting
out numbers, a long caw followed by a series of short caws (usually
made when a bird takes off from a perch), an echo-like "eh-aw"
sound, and more. These vocalizations vary by species, and within
each species vary regionally. In many species, the pattern and
number of the numerical vocalizations have been observed to change
in response to events in the surroundings (i.e. arrival or
departure of crows). Crows can hear sound frequencies lower than
those that humans can hear, which complicates the study of their
vocalizations.
Loud, throaty "caw-aw-ah"'s are usually used to indicate hunger or
to mark territory. When defending a nest site or food, crows will
usually enlarge their crest feathers and hunch their shoulders to
increase their size.Softer, gurgling sounds have also been observed
as a sort of beckoning call, or a call of affection. These noises
are emitted from within the throat of the bird, much like a cat's
purring.
Intelligence
As a group, the crows show remarkable examples of intelligence, and
Aesop's fable of
The Crow and the Pitcher shows that
humans have long viewed the crow as an intelligent bird. Crows and
ravens often score very highly on intelligence tests. Certain
species top the
avian
IQ scale. Wild hooded crows in Israel have learned to use bread
crumbs for bait-fishing. Crows will engage in a kind of mid-air
jousting, or air-"
chicken" to establish pecking order.
One species, the
New Caledonian
Crow, has also been intensively studied recently because of its
ability to manufacture and use its own
tools in
the day-to-day search for food. These tools include 'knives' cut
from stiff leaves and stiff stalks of grass. Another skill involves
dropping tough nuts into a heavy trafficked street and waiting for
a car to crush them open, and then waiting at pedestrian lights
with other pedestrians in order to retrieve the nuts.
On October 5, 2007, researchers
from the University of
Oxford
, England
presented
data acquired by mounting tiny video cameras on the tails of New
Caledonian Crows. It turned out that they use a larger
variety of tools than previously known, plucking, smoothing and
bending twigs and grass stems to procure a variety of foodstuffs.
Crows in
Queensland
, Australia have learned
how to eat the toxic cane toad by flipping
the cane toad on its back and violently stabbing the throat where
the skin is thinner, allowing the crow to access the non-toxic
innards; their long beaks ensure that all of the innards can be
removed. Recent research suggests that crows have the
ability to recognize one individual human from another by facial
features.
Colour and society
Extra-specific uses of colour in crow societies
Many crow species are all black. Most of their natural enemies, the
raptor or "
falconiformes", soar high above the trees, and
hunt primarily on bright, sunny days when contrast between light
and shadow is greatest. Crows usually hunt in groups of other
crows, called murders. Crows take advantage of this by maneuvering
themselves through the dappled shades of the trees, where their
black color renders them effectively invisible to their enemies
above , in order to set up complex ambush attacks . It is perhaps
here where we find the greatest difference between ravens and
crows—
ravens tend to soar high in the air as
raptors do. Fledglings are much duller than adults in
appearance.
While hawks tend to be the primary daytime predators of crows,
their most deadly predators, in many areas, are the owls that hunt
by night . Crows also will often mob owls much more fiercely when
they find them in daylight than the hawks and other raptors .
Frequently crows appear to "play" with hawks, taking turns
"
counting coup" while escorting the
raptor out of their territory. Their attacks on owls, on the other
hand, possess a definite serious quality.
Intra-specific uses of color in crow societies
Even in species characterized by being all black, one will still
occasionally find variations, most of which appear to result from
varying degrees of
albinism, such as:
- an otherwise all-black crow stunningly contrasted by a full set
of brilliant, pure-white primary feathers.
- complete covering in varying shades of grey (generally tending
toward the darker side).
- blue or red, rather than swarthy eyes (blue being more common
than red).
- Some combination of the above
The treatment of these rare individuals may vary from group to
group, even within the same species. For example, one such
individual may receive special treatment, attention, or care from
the others in its group , while another group of the same species
might exile such individuals, forcing them to fend for themselves.
The reason for such behaviors may relate to the fact that colorful
differences can draw attention from unwanted predators.
In culture and mythology
- See also Raven in
mythology and Cultural
depictions of ravens.
Crows, and especially
ravens, often feature in
European legends or
mythology as
portent or harbingers of doom or
death, because of their dark plumage,
unnerving calls, and tendency to eat
carrion. They are commonly thought to circle above
scenes of death such as
battles.
In
occult circles, distinctions are sometimes
made between crows and ravens. In mythology and folklore as a
whole, crows tend to be
symbolic more of
the spiritual aspect of death, or the transition of the spirit into
the
afterlife, whereas ravens tend more
often to be associated with the negative (physical) aspect of
death. However, few if any individual mythologies or folklores make
such a distinction, and there are ample exceptions. Another reason
for this distinction is that while crows are typically highly
social animals, ravens don't seem to congregate in large numbers
anywhere but:
- Near carrion where they meet seemingly by chance, or
- At cemeteries, where large numbers
sometimes live together, even though carrion there is no more
available (and probably less attainable) than any road or
field.
Compendium of Materia
Medica states that crows are kind birds that feed their
old and weakened parents; this is often cited as a fine example of
filial piety.
In mythology
A very incomplete list of deities associated with ravens includes
the eponymous
Pacific Northwest
Native figures
Raven and
Crow,
the ravens
Hugin and Munin,
who accompany the
Norse god
Odin, the
Celtic
goddesses the
Mórrígan
and/or the
Badb (sometimes considered
separate from Mórrígan), and
Shani, a
Hindu god who travels astride a crow.
In the
Epic of Gilgamesh,
the
Chaldean myth, the character
Utnapishtim releases a
dove and a raven to find land, however, the dove merely
circles and returns. Only then does Utnapishtim send forth the
raven, who does not return. Utnapishtim extrapolates from this that
the raven has found land, which is why it hasn't returned. This
would seem to indicate some acknowledgement of crow intelligence,
which may have been apparent even in ancient times, and to some
might imply that the higher intelligence of crows, when compared to
other birds, is striking enough that it was known even then.
In
Buddhism, the Dharmapala (protector of
the Dharma)
Mahakala is represented by a
crow in one of his physical/earthly forms.
Avalokiteśvara/
Chenrezig, who is reincarnated on Earth as the
Dalai Lama, is often closely associated
with the crow because it is said that when the first Dalai Lama was
born, robbers attacked the family home. The parents fled and were
unable to get to the infant Lama in time. When they returned the
next morning expecting the worst, they found their home untouched,
and a pair of crows were caring for the Dalai Lama. It is believed
that crows heralded the birth of the First, Seventh, Eighth,
Twelfth and Fourteenth Lamas, the latter being the current Dalai
Lama,
Tenzin Gyatso.Crows are
mentioned often in
Buddhism, especially
Tibetan disciplines.
According to Ovid's Metamorphoses, in classical mythology, when the
crow told the god
Apollo that his lover
Coronis was cheating on him with a mortal,
he became very angry, and part of that anger was directed at the
crow, whose feathers he turned from white to black.
Myths in India: In
Hinduism, it is believed
that people who died will take food and offerings through a variety
of crows called "Bali kākka". Every year people whose parents or
relatives died will offer food to crows as well as cows on the
Śrāddha day. A battle between
crows and owls is said to have inspired the final bloody night of
the
Mahabharatha war.
In
Chinese mythology, the world
originally had ten suns embodied as ten crows, which rose in the
sky one at a time. When all ten decided to rise at once, the effect
was devastating to crops, so the gods sent their greatest archer
Houyi, who shot down nine crows and spared
only one. Having a "crow beak" is a symbolic expression that one is
being a
jinx.
In culture
Literature and film
The
Child ballad The Three Ravens depicts three ravens
discussing whether they can eat a dead knight, but finds that his
hawk, his hound, and his true love prevent them; in the parody
version
The Twa Corbies, these guards have already
forgotten the dead man, and the ravens can eat their fill. Their
depiction of evil has also led to some exaggeration of their
appetite. In modern films such as
Pirates of the
Caribbean: Dead Man's Chest,
Damien:
Omen II,
The Crow and
Exorcist: The Beginning,
crows are shown tearing out people's eyes while they are still
alive. Crows have never been known for this behavior due to their
high preference for carrion. Crows are also one of the
investigation clues in the ABC TV series
FlashForward.And also in CWs Tv series
The Vampire Diaries and books, the main
character and other characters often see crows around, especially
Elena.They add on to the morose mood in some scenes.
Virus
The American crow is very susceptible to the
West Nile virus, a disease just recently
introduced in North America. American crows usually die within one
week of acquiring the disease with only very few surviving
exposure. Crows are so affected by the disease that their deaths
are now serving as an indicator of the West Nile Virus’ activity in
an area.
Status as an Endangered Species
Two species of crow have been listed as endangered by the US fish
and wildlife services: The
ʻAlalā and
the
Mariana Crow.The
American Crow, despite having its population
reduced by 45% since 1999 by the West Nile Virus, is considered a
Species of Least Concern.
See also
References
- Gill, B. J. (2003): Osteometry and 1: 43-58. (HTML
abstract)
- Worthy, Trevor H. & Holdaway, Richard N. (2002): The
lost world of the Moa: Prehistoric Life of New Zealand.
Indiana University Press,
Bloomington. ISBN 0-253-34034-9.
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