Corvus frugilegus

Geographic Range

Corvus frugilegus is found in the Palearctic region, across much of Europe and Asia. Two subspecies of rooks are recognized: C. f. frugilegus and C. f. pastinator . The geographic range of C. f. frugilegus extends from Ireland eastward across Europe into Russia, with southern boundaries as far as Turkey and Iran. Sporadic, localized populations can be found as far north as southern Sweden, Norway, and Denmark. Populations have also been introduced in New Zealand, where they flourish. During breeding and migration, C. f. frugilegus can be found in northern Russia and the Mediterranean area, respectively. The geographic range of C. f. pastinator , commonly known as the Oriental rook, extends from eastern Asia west into northern Mongolia. The two subspecies are generally geographically separated by the Altai Mountains.

• Biogeographic Regions
• palearctic palearctic
  • native native
• oceanic islands oceanic islands
  • introduced introduced

Habitat

Rooks are widely distributed across Europe and western Asia, preferring arable land, river plains, and steppe regions where soil is generally soft and fertile. In agricultural landscapes, rooks tend to avoid areas where winter cereal grains such as rye and wheat are grown, instead preferring areas in which softer and more easily-accessible spring cereals such as barley are grown. Spring cereals are an ideal food source for C. frugilegus due to easy foraging that results from their small height. River plains and steppe regions also serve as excellent habitats for rooks because their rich soil is usually teeming with insects, and soft ground makes foraging possible. Rooks can also be found in areas bordering cities and towns as long as large trees are available for cover and food is available for scavenging. Given their wide occupation of much of Europe and Asia, rooks are able to tolerate a large elevation range, from sea level to approximately 4000 m.

• Habitat Regions
• temperate temperate
• terrestrial terrestrial

• Terrestrial Biomes
• savanna or grassland savanna or grassland
• forest forest

• Other Habitat Features
• suburban suburban
• agricultural agricultural
• riparian riparian

Physical Description

Corvus frugilegus is similar in appearance to C. corone (carrion crow), another species of corvid . Though both species are covered in glossy black feathers with a metallic sheen, rooks are distinguishable from carrion crows by their slightly smaller size, distinct wedge-shape tail, light colored bill, and prominently-fingered wingtips. Rooks average 47 cm long and weigh 337 to 531 g, but are considered large when compared to most other corvid species. Rooks show weak sexual dimorphism, with males slightly larger than females. In rooks, wing length ranges from 290 to 330 mm (wingspan ranges from 81 to 94 cm) and tarsus length ranges from 52 to 58 mm. For their size, rooks have a relatively large bill (53 to 57 mm long) that tapers to a sharp point. This long, sharp bill aids in food retrieval and eating insects.

Corvus frugilegus frugilegus tends to have a longer, thicker beak than that of C. f. pastinator , as well as a larger area of bare skin covering the forehead, lores (skin between eye and bill on side of head), and gular area (skin that joins lower mandible to neck). Corvus frugilegus frugilegus also has a violet sheen to its black feathers, whereas C. f. pastinator has a greenish sheen. Juveniles of both subspecies are easily recognizable by their brown-toned feathers and fully-feathered face, which does not become bare until their first spring.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike
• male larger

Reproduction

Despite their highly social nature, rooks form pair bonds that lasts from several years to life. Rooks generally take mates when they are two years old. During the fall mating season, pair bonds nest together in communal roosts called rookeries until they return to individual nests to lay eggs. Despite hundreds of birds in a single rookery, rooks maintain their pair bonds through extensive communication. Though rooks are known for being monogamous, like other corvid species such as Corvus corax (common ravens) and C. corone (carrion crows), there have been reported instances of bigamy and occupation of a nest by multiple females.

• Mating System
• monogamous monogamous
• cooperative breeder cooperative breeder

Breeding and egg-laying usually begins around late February in Britain, but may be as late as April and May in central Europe and Russia where cold weather persists for a longer period of time. Rooks generally build nests in tall deciduous trees, though nests on the ground and in bushes are not uncommon. Nests consist of sticks and branches with a deep leaf, grass, and moss-lined cup. Rooks ( Corvus frugilegus ) lay two to seven (average four) blue-green eggs that are covered with brown and grey mottling. Rook eggs are very similar in appearance to those of ravens ( C. corax ), though slightly smaller, on average 40 mm long. After 16 to 18 days of incubation mainly by the female, the young hatch blind and helpless.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• oviparous oviparous

For the 16 to 18 day incubation period the female rook covers the eggs unless she has to briefly leave the nest, in which case the male takes over this duty. After hatching, the female tends to the young exclusively while the male delivers food. This continues for approximately the first ten days until the young become more self-sufficient, at which point the female joins the male in food gathering. At around 32 to 33 days old the young rooks fledge and leave the nest, but roost in nearby trees to remain close to the parents. The young continue their relationship with the parents for several weeks until they become fully independent. Even after reaching full maturity and independence, rooks generally remain members of their original rookery.

• Parental Investment
• altricial altricial
• male parental care male parental care
• female parental care female parental care
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • male
    • female
  • protecting
    • male
    • female
• pre-weaning/fledging
  • provisioning
    • male
  • protecting
    • male
    • female
• pre-independence
  • provisioning
    • male
    • female
  • protecting
    • male
    • female
• extended period of juvenile learning

Lifespan/Longevity

Not much is recorded on the lifespan of C. frugilegus , but like most Corvidae species, the rook is expected to live 15 to 20 years in the wild. According to the EURING European Longevity Records, the oldest rook found in the wild lived to be 22 years old. As is the trend, rooks in captivity may live for much longer. In a similar species, Corvus corax , the longest lifespan was recorded at 69 years for life in captivity.

Behavior

Rooks are highly social, living and interacting in large groups, although mating tends to monogamous. This bird species is largely arboreal and actively defends its territory. Rooks are active primarily during the day.

• Key Behaviors
• arboreal arboreal
• flies
• diurnal diurnal
• motile motile
• migratory migratory
• territorial territorial
• social social

Communication and Perception

Rooks have a distinct call that has been described as sounding like a “caw." When rooks are defending or establishing a territory, multiple “caws” are used. Rooks also have a snarling call, as well as a gull call, which are used when an intruder comes within a short distance of their nest. In order to remain in contact with other rooks, a single loud “caw” is used during both foraging and migration. However, it is believed that rooks mainly vocalize with their mate, rather than in other social interactions. Like other birds, rooks perform singing duets (usually with a mate) that are believed to create a stronger mating bond. Female rooks use frequent vocalizations, by means of a begging call, in order to establish a submissive state with their mate, as well as to show dependency towards the male. Rooks also rely heavily on vocal communication with their young during the first few days of hatching.

Auditory communication is vital to the rook. They have a sense of hearing which helps them distinguish amongst other populations and species. The rook is able to recognize the call of a mate or its young. In addition to vocalizations, rooks also rely on visual communication, which becomes increasingly more important once young are able to open their eyes. Pecking is another form of communication, when an intruder rook comes too close to a territory; pecking attacks can occur usually resulting in the retreat of the intruder.

• Communication Channels
• visual visual
• tactile tactile
• acoustic acoustic

• Other Communication Modes
• duets duets

• Perception Channels
• visual visual
• polarized light polarized light
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Rooks are opportunistic feeders. As omnivores, they eat any edible food item. Due to the strength and size of the bill, rooks are often found probing the ground in search of earthworms or other insects. Rooks also ingest small acorns, small fruits, and cereal grains. When the opportunity arises, rooks prey on small mammals, small birds, carrion, and eggs of the same species. They also have been known to act as “nest predators”, attacking the nests of other species of birds in order to eat the hatchlings and eggs.

Rook feeding habits often vary due to the location of their nest. Unlike those occurring in natural areas as above, those that live near urban sites also act as scavengers and take advantage of trashcans as well as abandoned food. Most rooks spend much of their time foraging at dawn and dusk. Primarily searching at dawn, rooks will pick through garbage bags to obtain food. However, they have been seen foraging during the day. Like all corvids , rooks store their food.

• Primary Diet
• carnivore carnivore
  • eats terrestrial vertebrates
  • eats eggs
  • insectivore insectivore
  • eats non-insect arthropods
  • vermivore
  • scavenger scavenger
• herbivore herbivore
  • frugivore frugivore
  • granivore granivore
• omnivore omnivore

• Animal Foods
• birds
• mammals
• eggs
• carrion carrion
• insects
• terrestrial worms
• aquatic crustaceans

• Plant Foods
• seeds, grains, and nuts
• fruit

• Foraging Behavior
• stores or caches food stores or caches food

Predation

Little is known about predators of rooks. However, they appear to have similar predators to Corvus corax or Corvus brachyrhynchos , both similar and closely related species in the Family Corvidae . Owls, such as Bubo virginianus , hawks, or even intruding species of Corvidae tend to be the primary predators of rooks. Raptorial bird species prey on fledglings from nests more often than attacking adults. Humans may also pose as a threat to some species due to increasing tolerance of human presence. Humans are a threat due to shootings and habitat destruction of rooks.

Ecosystem Roles

Rooks have numerous roles in the ecosystem. They serve as hosts for numerous protozoan organisms such as trypanosomes and leucocytozoans. Such organisms are generally not pathogenic and merely occupy rooks as vectors. While rook hosting of these organisms does not directly cause it any harm, it makes infection of other species possible. In this way, rooks sustain the lifecycle of these organisms.

Rooks also serve as hosts for oribatid mites, among other types of mites. Oribatid mites are soil mites, and feed on dead plant and fungal material. These mites live in the feathers of rooks, where it is believed they consume fungi. Such a relationship does not harm rooks, it is actually beneficial, though its results are not readily noticeable.

Lastly, rooks play a key role in seed dispersal as they crack open and consume cereal grains such as barley. Without birds and small animals to crack open seeds and remove them from the plant, seed dispersal for cereal grains could be problematic or less efficient.

• Ecosystem Impact
• disperses seeds
• soil aeration soil aeration

Economic Importance for Humans: Positive

While many farmers claim that C. frugilegus does more harm than good, recent studies suggest that 60 to 90% of insects consumed by rooks are agricultural pests. If this is the case, large numbers of rooks may have some impact on pest insect populations. Rooks are also known to dig into the soil in search of insects, so this may have a slight aeration effect which is particularly important in agricultural environments. Lastly, rooks play an important role in seed dispersal as they consume and crack open cereal grains.

• Positive Impacts
• controls pest population

Economic Importance for Humans: Negative

Rooks are commonly referred to as "agricultural pests", meaning they cause the loss and destruction of commercial crops. When foraging for food, rooks are often found in farmland crops, taking advantage of the cereals and grains. This can lead to an economic decline for farmers, as well as any person or company that may use the farmer for food. However, rooks are only known to cause damage to crops if the preferred food is not available.

As well as being agricultural pests, rooks that live in urban areas are likely to get into garbage and rip open the bags, which can in turn cause problems for humans.

• Negative Impacts
• crop pest

Conservation Status

Corvus frugilegus is classified as a species of least concern on the IUCN's Red List of Threatened Species. Corvus frugilegus is abundant and is able to maintain stable populations in its habitat.

Additional Links

Encyclopedia of Life

Contributors

Lauren Carlson (author), Radford University, Kelsey Townsend (author), Radford University, Christine Small (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

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