Corvus corax characteristics, habitat, reproduction, feeding

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Sherman Hoover

The common raven (Corvus corax) is a bird of the order Passeriformes of the Corvidae family. They are very common omnivorous birds in the areas where it is distributed. In general, these corvids are sedentary birds. In contrast, some populations to the north may migrate south during winter or disperse to more favorable nearby regions..

They are monogamous and very territorial birds for much of their life. Juveniles are usually gregarious birds and very curious about new objects or experiences. On the other hand, adults after reaching maturity are suspicious of any new situation. They are birds very adaptable to a large number of environments, and can be considered a pest in those places where their reproduction is very successful..

Corvus corax (Common Raven) By © Frank Schulenburg

Juveniles are generally grouped in communal winter shelters. Such shelters can function as information centers on the location of ephemeral and quality food sources..

These birds are capable of storing high-fat foods for times of low resource availability. In addition, they are able to remember the hiding places they used.

They have practically no predators due to the fact that they are very intelligent birds. Despite this, juvenile, non-reproductive specimens and chicks are especially susceptible to attack by birds of prey such as hawks and eagles..

Crows may also play an ecological role in seed dispersal on some islands and archipelagos where this corvid is found..

In many cases, the passage of certain seeds through the bird's digestive tract improves their germination and subsequent establishment. The crows that inhabit these islands are notoriously more frugivorous than the populations that inhabit continental environments..

Article index

  • 1 General characteristics
    • 1.1 Size and weight
    • 1.2 Wingspan
    • 1.3 Bill and plumage
    • 1.4 Subspecies
  • 2 Habitat and distribution
    • 2.1 Habitat
    • 2.2 Distribution
  • 3 Playback
    • 3.1 Nesting
  • 4 Food
    • 4.1 Resources consumed
  • 5 Conservation status
  • 6 Behavior
    • 6.1 Association with predators
  • 7 References

General characteristics

Size and weight

They are among the largest and heaviest birds of the order Passeriformes in the world. A fully grown common raven is between 50 and 70 cm in total length.

Weight can often range from 750g to 1.6kg. They are long-lived birds, in nature some ringed individuals can exceed 14 years of life. Other captive-bred birds can live for about 40 years.

Corvus corax in its natural habitat By Membeth / CC0

Individuals that live in more temperate areas tend to be larger and with more developed beaks than those that live in warmer areas. The latter is directly related to the type of resources they consume in both types of habitat..

Wingspan

The wingspan of the largest specimens can exceed 120 cm and even reach more than 1.5 meters.

Beak and plumage

The beak of these birds is curved distally, it is thick and strong and of dark coloration. The eyes of these birds are generally brown in color and the plumage is typically black. The feathers on the body have blue and purple hues or reflections. In non-reproductive specimens the plumage is more opaque and with greyish tones..

Subspecies

Because this species has a wide geographic distribution, around 9 subspecies have been defined. These subspecies are distinguished only by morphometric characters since the appearance of these varieties is very similar.

  • Corvus corax canariensis
  • Corvus corax corax
  • Corvus corax varius
  • Corvus corax subcorax
  • Corvus corax tingitanus
  • Corvus corax tibetanus
  • Corvus corax kamtschaticus
  • Corvus corax principalis
  • Corvus corax sinuatus

Habitat and distribution

Habitat

This species is found in various habitats in its range, occupying environments from sea level to 5000 meters in elevation and even above 6000 meters in the Himalayas..

Crows prefer to inhabit open and clear areas with little tree cover to carry out their foraging and nesting activities..

The coastal areas and cliffs are the preferred areas to establish their nests. However, their populations are currently increasing in some urban areas such as California, where they are favored by waste from human activities..

They can also occupy forested areas in boreal regions and coastal areas of the Arctic, North America, Europe, North Africa, various islands in the Pacific Ocean..

Distribution

Crows are one of the most widely distributed birds in the Corvidae family. They occupy a large part of the Holartic region, both in the Nearctic subregion and in the Palearctic region. Several individuals are occasionally seen in Nicaragua and Guatemala, well south of their typical range..

Distribution of the common raven (Corvus corax) By Corvus_corax_map.jpg: Engineer111derivative work: Totodu74 / CC BY-SA (http://creativecommons.org/licenses/by-sa/3.0/)

Reproduction

Crows establish lifelong mates. Generally there is a series of rituals in which they demonstrate their ability to fly, their abilities in obtaining food, and their intelligence. Once a pair is established, it tends to nest every year in the same place..

The laying of eggs of this species occurs mainly in February in almost all areas where it is distributed. However, in the northernmost regions such as Greenland, Tibet and Siberia, spawning occurs later in April..

Crows' nests are large and bulky. They are built with dry branches and are lined with fine roots, grass, litter and even dry skin of mammals inside for greater protection of the clutch.

Corvus corax nest By Medenica Ivan / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

In the wild they usually nest on cliffs or in the lower zone of the canopy in coniferous forests and forests with broadleaf trees. On the other hand, nests can also be established on building projections, light poles, antennas and other varied structures in those urban populations.

Nesting

The females are the only ones that incubate the eggs that vary in quantity, from three to seven, depending on the resources available in the area they occupy..

The most successful clutches are those located where there are permanent sources of food, such as garbage dumps..

Clutch of Common Ravens By © noisytoy.net / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

On several occasions the presence of albino chicks have been reported. The rearing success of these chicks is significantly lower than that of normal chicks. Only very rarely have fully developed albino adults been observed.

In this video you can see a mating dance between two specimens:

Feeding

Common crows in general are birds that move in groups when feeding and tend to disperse when they begin to compete for resources..

They are also capable of stealing or attacking food caches made by other crows, suggesting remarkable learning and the use of tactics that have likely evolved from cognitive selection pressures in this species..

On the other hand, crows have an extraordinary spatial memory to accurately remember the multiple stores of provisions.

Crows are considered omnivorous birds or opportunistic scavengers that gather in unfamiliar groups to exploit a resource. These group associations provide them with greater security when facing predators such as wolves or overcoming the food defense of more dominant birds of the same species..

Because it is a species that has a wide geographic distribution, the resources it uses vary widely depending on the area or environment it occupies..

Consumed resources

In general, they can consume a wide variety of animals and plants. They can feed on adult birds, chicks, and eggs. They can also capture small mammals, sick and dying mammals, amphibians and assorted reptiles, small turtles, fish and a great diversity of invertebrates..

In many localities they are observed scavenging through garbage, manure, carrion and are also capable of consuming plant parts of various agricultural crops..

State of conservation

This species maintains a wide geographic range, with generally large populations in all the areas it occupies and also in many sectors the population trends are increasing. Due to these reasons, the species is in the category of Least Concern according to the IUCN.

In the past, the species was persecuted and extirpated in many regions of central Europe due to the superstitions that revolved around this bird. Currently, in these places it is no longer persecuted and there is a pattern of recolonization of areas where the species previously existed..

In some regions of the United States, where crow populations have experienced a significant increase in recent decades (California, Oregon, Utah and Nevada), these birds are selectively eliminated..

They are generally killed by shooting or massive poisoning, as they are considered pests, in order to obtain temporary benefits for cereal crops that are often invaded by these birds..

The most immediate threats to this species are extensive agriculture and the continued elimination of natural ecosystems..

Behaviour

The crows Corvus corax they are extremely intelligent birds, they have one of the largest and most developed brains among birds.

The raven has been identified as a bird capable of solving complex problems and with a surprising capacity for learning such as imitation, tactical skills and the acquisition of motor skills, as well as having a complex communication system.

In certain localities, common ravens can set behaviors in a traditional way, which are not observed in other populations of the species..

When flocks of juveniles gather, specimens that have not managed to feed well know the location of food sources from more experienced specimens who function as leaders of these groups..

These groups of juveniles usually displace adult territorial couples that defend a food source within their territory. Typically, these groups continually recruit other individuals, making the group larger and more competitive for resources..

On the other hand, their hiding places are chosen with caution since these birds can also steal the stores of their congeners once they see where the food was hidden. These birds have excellent observational memory.

Association with predators

These birds are capable of associating with predators such as gray wolves in the winter time. In this way, in those areas where the distributions of both species overlap, crows can guarantee a constant supply of food during this time of scarce resources..

The ravens then act as a kleptoparasitic species. In this way, these birds are in continuous monitoring of the wolf packs when they rest, move or hunt prey..

References

  1. Austin, J. E., & Mitchell, C. D. (2010). Characteristics of common raven (Corvus corax) predation on sandhill crane (Grus canadensis) eggs. Northwestern Naturalist, 91(1), 23-29.
  2. BirdLife International 2017. Corvus corax (amended version of 2016 assessment). The IUCN Red List of Threatened Species 2017: e.T22706068A113271893. https://dx.doi.org/10.2305/IUCN.UK.2017-1.RLTS.T22706068A113271893.en. Downloaded on 09 March 2020.
  3. Bugnyar, T., & Kotrschal, K. (2002). Observational learning and the raiding of food caches in ravens, Corvus corax: is it 'tactical'deception?. Animal behavior, 64(2), 185-195.
  4. Bugnyar, T., & Heinrich, B. (2005). Ravens, Corvus corax, differentiate between knowledgeable and ignorant competitors. Proceedings of the Royal Society B: Biological Sciences, 272(1573), 1641-1646.
  5. Bugnyar, T., Stoewe, M., & Heinrich, B. (2007). The ontogeny of caching in ravens, Corvus corax. Animal Behavior, 74(4), 757-767.
  6. Fritz, J., & Kotrschal, K. (1999). Social learning in common ravens, Corvus corax. Animal Behavior, 57(4), 785-793.
  7. Heinrich, B. (1988). Winter foraging at carcasses by three sympatric corvids, with emphasis on recruitment by the raven, Corvus corax. Behavioral Ecology and Sociobiology, 2. 3(3), 141-156.
  8. Marquiss, M., & Booth, C. J. (1986). The diet of Ravens Corvus corax in Orkney. Bird Study, 33(3), 190-195.
  9. Nogales, M., HernÁndez, E. C., & ValdÉs, F. (1999). Seed dispersal by common ravens Corvus corax among island habitats (Canarian Archipelago). Ecoscience, 6(1), 56-61.
  10. Stahler, D., Heinrich, B., & Smith, D. (2002). Common ravens, Corvus corax, preferentially associate with gray wolves, Canis lupus, as a foraging strategy in winter. Animal Behavior, 64(2), 283-290.
  11. Wright, J., Stone, R. E., & Brown, N. (2003). Communal roosts as structured information centers in the raven, Corvus corax. Journal of Animal Ecology, 72(6), 1003-1014.

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