Instruct: Given a question, retrieve relevant documents that answer the question.
Query: How big can a Eurasian eagle-owl get?
The Eurasian eagle-owl ("Bubo bubo") is a species of eagle-owl that resides in much of Eurasia. It is also called the European eagle-owl and in Europe, it is occasionally abbreviated to just eagle-owl. It is one of the largest species of owl, and females can grow to a total length of 75 cm (30 in), with a wingspan of 188 cm (6 ft 2 in), males being slightly smaller. This bird has distinctive ear tufts, with upper parts that are mottled with darker blackish colouring and tawny. The wings and tail are barred. The underparts are a variably hued buff, streaked with darker colour. The facial disc is poorly developed and the orange eyes are distinctive.
Even those near the northern limits of their range, where winters are harsh and likely to bear little in food, the eagle-owl does not leave its native range. There are cases from Russia of Eurasian eagle-owls moving south for the winter, as the icebound, infamously harsh climate there is too severe even for these hardy birds and their prey. Similarly, Eurasian eagle-owls living in the Tibetan highlands and Himalayas may in some cases vacate their normal territories when winter hits and move south. Even in those two examples, there is no evidence of consistent, annual migration by Eurasian eagle-owls and the birds may eke out a living on their normal territories even in the sparsest times.
Throughout the western Mediterranean region, the Eurasian Eagle-Owl is something of a specialist on a single prey species: the European rabbit. The rabbit historically reached extremely high densities in Iberian scrub, i.e. more than 40 per every 1 square hectare (2471 square acres). In central Spain, up to 73.1% of the prey that were recorded for Eurasian eagle-owls, by number, can be rabbits. Where still available, they are also the main prey in Portugal and central France. However, following the devastation of the wild rabbit due to rabbit haemorrhagic disease, the local eagle-owls have frequently had to adapt to other, often smaller, prey. On the other hand, given the now much reduced numbers of rabbits, the eagle-owls still regularly select rabbits, seemingly out of proportion to their commonality. Although large mature wild rabbits commonly weigh , the eagle-owls usually hunt smaller specimens, often with an average weight around , with young rabbits usually selected in spring and summer and subadults selected in the autumn and winter. This is largely due to the behaviour of rabbits, with younger rabbits being forced to distribute following weaning, being less cautious in behaviour and occupying less primary habitat, thus being forced out of the confines of their burrows more regularly than mature adults. However, the estimated average weight of rabbits taken can be variable, reported from as little as in a study from Spain to as much as in the Netherlands.
Owls, which may have dissimilar periods of activity, are not entirely exempt from golden eagle predation either. Several species have been recorded as prey, especially in Northern Europe, Slovakia (where owls make up 2.4% of prey remains) and some parts of the Western United States. Species hunted have ranged in size from tiny Eurasian pygmy owl ("Glaucidium passerinum") and little owl ("Athene noctua") to the formidable, large great horned, Eurasian eagle and great gray owls ("Strix nebulosa"). Barn owls ("Tyto alba") have been predated by golden eagles in both North America and Eurasia. On Santa Rosa and Santa Cruz Islands, barn owls made up 4.5% of the diet, the largest known occurrence of that species in the eagles' diet. However, the great horned owl is the owl species that occurs most regularly in the diet of North American golden eagles. In Europe, golden eagles are relatively minor predators of owls compared to Eurasian eagle-owls and northern goshawks. The primary owls hunted by European eagles are Ural owls ("Strix uralensis") and short-eared owls ("Asio flammeus"). Few eye-witness accounts are known of owl predation, but one violent mid-day confrontation between a golden eagle and an adult great horned owl was witnessed in Jefferson County, Colorado. Although this owl was about a third of the eagle's weight, it was able to land some damaging blows on the larger bird. In the end, despite its wounds, the eagle was victorious over the dead owl. A case of kleptoparasitism by a golden eagle on a great horned owl has been recorded. Although the Eurasian eagle-owl is preyed upon by golden eagles (4 confirmed cases of golden eagles killing eagle-owls in Europe), in one case a golden eagle (age unspecified) was found amongst the prey in an eagle-owl nest.
In the Iberian peninsula, the Eurasian eagle-owl is part of a complex guild of predators that have evolved to survive mostly on European rabbits. Among this guild, golden eagles ("Aquila chrysaetos") were recorded per one study to rely on rabbits for 40% of the diet, the eagle-owl for 49% of the diet, the Spanish imperial eagle ("Aquila adalberti") for 50% of the diet, the Bonelli's eagle ("Aquila fasciata") for 61% of the diet and the Iberian lynx ("Lynx pardinus") for 79% of the diet. Elsewhere, the Spanish imperial eagle and eagle-owl are considered to outflank the golden and even the Bonelli's eagle as the most specialized avian predator of rabbits in the Iberian region. Other predators, such as common buzzard ("Buteo buteo"), northern goshawk ("Accipiter gentilis") black kite ("Milvus migrans") Iberian wildcat ("Felis silvestris tartessia"), red fox, stone marten ("Martes foina") and introduced Egyptian mongoose also prey heavily on rabbits in Spain, but are more generalized and less reliant than the above predators. All these powerful predators do not generally compete directly for food but conflicts may ensue over the rights to territories and nesting sites amongst the birds. Being nocturnal in activity, however, the Eurasian eagle-owl does not tend to compete as directly as do the three eagle species and even these are discreetly segregated by habitat preferences, the goldens preferring open, steep cliffs, the Bonelli's favoring densely vegetated areas mixed with rocky spots and the imperial favoring relatively flat open woodlands. Among these eagles, the golden eagle tends to have the most similar habitat preferences to the Eurasian eagle-owl and across a broad band of overlapping distribution, the two are considered nearly ecological equivalents by day and night. However, good-sized female golden eagles are up to twice as heavy as an average eagle-owl, so seem to have a considerable advantage in size and power. Conversely, to support their large size and large territory needs, the golden eagle cannot survive on small and diverse prey nearly as successfully as the eagle-owl. Among the Iberian peninsula rabbit-eating guild, the species with wider ranges, the eagle-owl and the golden and Bonelli's eagles, have had some degree of success living off of alternate prey following the devastation of the rabbit population due to rabbit haemorrhagic disease. The two rabbit predators endemic to Iberia, the Iberian lynx and Spanish imperial eagle, have been devastated by the reduction and other causes and both are threatened species today.
The European jackal is the largest of the golden jackals, with animals of both sexes measuring 120–125 cm (47–49 in) in total length and 10–13 kg (20–29 lb) in body weight. One adult male in North-Eastern Italy is recorded to have reached 14.9 kg (33 lb). The fur is coarse, and is generally brightly coloured with blackish tones on the back. The thighs, upper legs, ears and forehead are bright reddish chestnut. Jackals in Northern Dalmatia have broader than average skulls, which is thought to result from human induced isolation from other populations, thus resulting in a new morphotype.
Eurasian beavers are one of the largest living species of rodents and are the largest rodent native to Eurasia. They weigh around . In Norway, adult males average while females average , while another study found adults from the same country to average . By the average weights known, the Eurasian beaver appears to be the world's second heaviest rodent behind the capybara, but averaging slightly larger and heavier than the North American beaver. While the largest specimen confirmed on record weighed , the Smithsonian has reported that this species can exceptionally exceed . Typically, the head-and-body length is and the tail length is .
The Harrier is similar to the English Foxhound, but smaller. Harriers stand between 19 and 21 inches at the shoulder, and adults weigh between 45 and 65 lbs. They do shed, have short hair and hanging ears, and come in a variety of color patterns. A humorous, description of a Harrier is that of "a Beagle on steroids" but it resembles an English Foxhound. It is a muscular hunting hound with a small, hard coat. It has large bones for stamina and strength. The Harrier is slightly longer than tall, with a level topline. The tail is medium-length, carried high, but is not curled over the back. The skull is broad with a strong square muzzle. The rounded ears are pendant, and the eyes are either brown or hazel. The wide nose is black. The expression is mellow when the dog is relaxed and alert when he is excited. The teeth should meet in a scissors or level bite. The feet are tight and cat-like, and the front toes may turn inward.
Common ostriches usually weigh from , or as much as two adult humans. The Masai ostriches of East Africa ("S. c. massaicus") averaged in males and in females, while the nominate subspecies, the North African ostrich ("S. c. camelus"), was found to average in unsexed adults. Exceptional male ostriches (in the nominate subspecies) can weigh up to . At sexual maturity (two to four years), male common ostriches can be from in height, while female common ostriches range from tall. New chicks are fawn in colour, with dark brown spots. During the first year of life, chicks grow at about per month. At one year of age, common ostriches weigh approximately . Their lifespan is up to 40–45 years.
The largest recorded egg is from a whale shark, and was in size. Whale shark eggs typically hatch within the mother. At and up to , the ostrich egg is the largest egg of any living bird, though the extinct elephant bird and some dinosaurs laid larger eggs. The bee hummingbird produces the smallest known bird egg, which weighs half of a gram (around 0.02 oz). Some eggs laid by reptiles and most fish, amphibians, insects and other invertebrates can be even smaller.
Bustards are all fairly large with the two largest species, the kori bustard ("Ardeotis kori") and the great bustard ("Otis tarda"), being frequently cited as the world's heaviest flying birds. In both the largest species, large males exceed a weight of , weigh around on average and can attain a total length of . The smallest species is the little brown bustard ("Eupodotis humilis"), which is around long and weighs around on average. In most bustards, males are substantially larger than females, often about 30% longer and sometimes more than twice the weight. They are among the most sexually dimorphic groups of birds. In only the floricans is the sexual dimorphism reverse, with the adult female being slightly larger and heavier than the male.
A male African forest elephant rarely exceeds 2.5 m (8.2 ft) in height, considerably smaller than the bush species which is usually over 3 m (9.8 ft) and sometimes almost 4 m (13.1 ft) tall. "L. cyclotis" reportedly weighs around , with the largest specimens attaining . Pygmy elephants of the Congo Basin, presumed to be a subgroup of "L. cyclotis", have reportedly weighed as little as as adults.
It is a very large bear, the largest in Eurasia, with a body length of 2.4 meters, to 3 meters tall on hind legs and a weight up to 650 kg (1433 lbs). It is nearly the size of the Kodiak bear; however, the skull is broader than that of the Ussuri brown bear, and compared to that of the Kodiak bear, the breadth of the skull is much greater in proportion to its length, the anterior narial opening is much shorter, and the molars differ in relative size and form. The greatest skull length for males is 40.3–43.6 cm and 25.8–27.7 cm wide, while the skulls of females measure 37.2–38.6 cm in length and 21.6–24.2 cm in width. Fur colour is predominantly dark brown with a violet tint. Light coloured individuals are rarely encountered.
Predators of the water rail include a number of mammals and large birds. The American mink was partly responsible for the extinction of the Icelandic population, and cats and dogs have also been recorded as killing this species. At least locally, otters will also eat rails and other water birds. The Eurasian bittern, another reed bed bird, will consume rails, as will grey herons. Water rails are particularly vulnerable to the heron when forced out of the cover of the reeds by very high tides. Wetland-hunting harriers are predictable predators, but more unusually, the rail has also been recorded as a prey item of the tawny owl, short-eared owl, Eurasian eagle-owl, greater spotted eagle, common kestrel, and night-hunting peregrine falcons.
The golden jackal ("Canis aureus") is a wolf-like canid that is native to Southeast Europe, Southwest Asia, South Asia, and regions of Southeast Asia. Compared with the Arabian wolf, which is the smallest of the gray wolves ("Canis lupus"), the jackal is smaller and possesses shorter legs, a shorter tail, a more elongated torso, a less-prominent forehead, and a narrower and more pointed muzzle. The golden jackal's coat can vary in color from a pale creamy yellow in summer to a dark tawny beige in winter. It is listed as Least Concern on the IUCN Red List due to its widespread distribution and high density in areas with plenty of available food and optimum shelter.
The smallest family members are the closely related short-tailed pygmy tyrant and black-capped pygmy tyrant from the genus "Myiornis" (the first species usually being considered marginally smaller on average). These species reach a total length of and a weight of 4–5 grams. By length, they are the smallest passerines on earth, although some species of Old World warblers apparently rival them in their minuscule mean body masses if not in total length. The minuscule size and very short tail of the "Myiornis" pygmy tyrants often lend them a resemblance to a tiny ball or insect. The largest tyrant flycatcher is the great shrike-tyrant at and . A few species such as the streamer-tailed tyrant, scissor-tailed flycatcher and fork-tailed flycatcher have a larger total length (up to ), but this is mainly due to their extremely long tails; the fork-tailed flycatcher has relatively the longest tail feathers of any known bird.
The female common ostrich lays her fertilised eggs in a single communal nest, a simple pit, deep and wide, scraped in the ground by the male. The dominant female lays her eggs first, and when it is time to cover them for incubation she discards extra eggs from the weaker females, leaving about 20 in most cases. A female common ostrich can distinguish her own eggs from the others in a communal nest. Ostrich eggs are the largest of all eggs, though they are actually the smallest eggs relative to the size of the adult bird — on average they are long, wide, and weigh , over 20 times the weight of a chicken's egg and only 1 to 4% the size of the female. They are glossy cream-coloured, with thick shells marked by small pits.
About 400 bird species have been recorded in Ireland. Many of these species are migratory. There are Arctic birds, which come in the winter, and birds such as the swallow, which come from Africa in the summer to breed. Many birds which are common residents in Britain and continental Europe are rare or unusual in Ireland, examples include the tawny owl, willow tit, marsh tit, nuthatch, and all woodpecker species except the recently established great spotted woodpecker. These are birds which do not move great distances and their absence may be due to Ireland's early isolation, but also Ireland's mild weather means early breeding and choice of best habitats which gives residents an advantage over visitors.
The golden jackal is similar to the gray wolf but is distinguished by its smaller size, lighter weight, more elongated torso, less-prominent forehead, shorter legs and tail, and a muzzle that is narrower and more pointed. The legs are long in relation to its body, and the feet are slender with small pads. Males measure in body length and females . Males weigh and females weigh . The shoulder height is for both. In comparison, the smallest wolf is the Arabian wolf ("Canis lupus arabs"), which weighs on average .
The African bush elephant is the largest and heaviest land animal on Earth, being up to tall at the shoulder and in weight (a male shot in 1974, near Mucusso, southern Angola). On average, males are about tall at the shoulder and in weight, while females are much smaller at about tall at the shoulder and in weight. Elephants attain their maximum stature when they complete the fusion of long-bone epiphyses, occurring in males around the age of 40 and females around the age of 25. Their large size means that they must consume around 50 gallons of water every day in order to stay hydrated.
The largest social wasp is the Asian giant hornet, at up to in length. The various tarantula hawk wasps are of a similar size and can overpower a spider many times its own weight, and move it to its burrow, with a sting that is excruciatingly painful to humans. The solitary giant scoliid, "Megascolia procer", with a wingspan of 11.5 cm, has subspecies in Sumatra and Java; it is a parasitoid of the Atlas beetle "Chalcosoma atlas". The female giant ichneumon wasp "Megarhyssa macrurus" is long including its very long but slender ovipositor which is used for boring into wood and inserting eggs. The smallest wasps are solitary chalcid wasps in the family Mymaridae, including the world's smallest known insect, "Dicopomorpha echmepterygis" (139 micrometres long) and "Kikiki huna" with a body length of only 158 micrometres, the smallest known flying insect.
The Eurasian eagle-owl ("Bubo bubo") may well be the most powerful extant species of owl, able to attack and kill large prey far beyond the capacities of most other living owls. However, the species is even more marked for its ability to live on more diverse prey than possibly any other comparably sized raptorial bird, which, given its considerable size, is almost fully restricted to eagles. This species can adapt to surprisingly small prey where it is the only kind available and to large prey where it is abundant. Eurasian eagle-owls feed most commonly on small mammals weighing or more, although nearly 45% of the prey species recorded have an average adult body mass of less than . Usually 55-80% of the food of eagle-owls is mammalian.
The Eurasian eagle-owl is a member of the genus "Bubo", which may include either 22 or 25 extant species. Almost all the larger owl species in the world today are included in "Bubo". Based on an extensive fossil record and a central distribution of extant species on that continent, the "Bubo" appears to have evolved into existence in Africa, although early radiations seem to branch from southern Asia as well. Two genera belonging to the scops owls complex, the giant scops owls ("Otus gurneyi") found in Asia and the "Ptilopsis" or the white-faced scops owl found in Africa, although firmly ensconced in the scops owl group, appear to share some characteristics with the eagle-owls. The "Strix" is also related to the "Bubo" and is considered a "sister complex", with the "Pulsatrix" possibly being intermediate between the two. The Eurasian eagle-owl appears to represent an expansion of the genus "Bubo" into the Eurasian continent. A few of the other species of "Bubo" seem to have been derived from the Eurasian eagle-owl, making it a "paraspecies", or they at least share a relatively recent common ancestor. The Pharaoh eagle-owl, distributed in the Arabian Peninsula and sections of the Sahara Desert through North Africa where rocky outcrops are found, was until recently considered a subspecies of the Eurasian eagle-owl. It appears that the Pharaoh eagle-owl differs about 3.8% in mitochondrial DNA from the Eurasian eagle-owl, well past the minimum genetic difference to differentiate species of 1.5%. Smaller and paler than Eurasian eagle-owls, the Pharaoh can also be considered a distinct species largely due to its higher pitched and more descending call and the observation that Eurasian eagle-owls formerly found in Morocco ("B. b. hispanus") apparently did not breed with the co-existing Pharaoh eagle-owls. On the contrary, the race still found together with the Pharaoh eagle-owl in the wild ("B. b. interpositus") in the central Middle East has been found to interbreed in the wild with the Pharaoh eagle-owl, although genetical materials have indicated "interpositus" may itself be a distinct species from the Eurasian eagle-owl, as it differs from the nominate subspecies of the Eurasian eagle-owl by 2.8% in mitochondrial DNA. The Indian eagle-owl was also considered a subspecies of Eurasian eagle-owl until recently, but its smaller size, distinct voice (more clipped and high-pitched than Eurasians), and the fact that it is largely allopatric in distribution (filling out the Indian subcontinent) with other Eurasian eagle-owl races has led to it being considered a distinct species. The mitochondrial DNA of the Indian species also appears considerably distinct from the Eurasian species. The Cape eagle-owl ("B. capensis") appears to represent a return of this genetic line back into the African continent, where it leads a lifestyle similar to northern eagle-owls albeit far to the south. Another offshoot of the northern "Bubo" group is the snowy owl. It appears to have separated from other "Bubo" at least 4 million years ago.
Most dietary studies place the average weight of Eurasian eagle-owl prey in the zone of , thus the species fits well within the rule of thumb that most prey weigh no more than 20% of the raptorial bird's own weight. It should be noted that the average prey weight in comparison to the eagle-owl's body mass is reportedly average and unremarkable for both owls and raptors in general, the average prey per one study was 7.2% of the eagle-owls’ body mass. The European raptorial birds most likely to attack prey of a relatively large size compared to themselves were the black kite ("Milvus migrans"), whose average prey was 35.7% of its own weight, and the Eurasian pygmy owl ("Glaucidium passerinum"), whose average prey was 31.7% of its own weight. On the other hand, when rabbit numbers were at their peak, the average prey mass in Spain may range up to at least 55% of the eagle-owls’ own body mass in that population. A raptorial prey comparison estimated that the mean prey weight for eagle-owls in Europe was as a mean among 5 main regions, the highest of any owl but similar or slightly lighter than the European average for northern goshawks ("Accipiter gentilis") and considerably lower only than two widespread European eagles. Per that study the average prey weight of the great horned owl in 4 North American regions was much lower (averaging only ). In Mediterranean scrub, the average mammalian prey of the Eurasian eagle-owl was nearly five times heavier than those of great horned owls from similar habitats in Chile, California and Colorado, where in combination the horned owl's mammalian food averaged . However, a comparison between eagle- and horned owls based upon six comparable biomes in the Americas and Eurasia found the great horned owl's prey averaged , improbably slightly higher than the eagle-owl at . If known Asian studies are mixed with European ones, the average prey weight for the Eurasian eagle-owl overall may also roughly be . Among sympatric owls in Europe, the mean prey weight of long-eared owls ("Asio otus") was found to be , the tawny owl ("Strix aluco") took prey weighing a mean of (though locally can be as high as ) and short-eared owls ("Asio flammeus") mean prey weigh was . A study in Finland seeking to distinguish the differences in prey taken by females and smaller male eagle-owls found that the two sexes prey averaged and , respectively. The species taken as food by the two sexes there were largely the same but the female simply often caught the larger prey individuals.
Equally or even more so than the great horned owl, the Eurasian eagle-owl is a threat to any smaller type of raptor it encounters, whether other owls or diurnal birds of prey. All told, more than 20 species of accipitrid, 15 species of owl and 9 species of falcon have been found amongst their prey. The Eurasian eagle-owl is the primary predator of other birds of prey throughout Eurasia, not even the prolific raptor-killing northern goshawk ("Accipiter gentilis") equals the sheer number of raptors taken. Up to 6% of the overall food by number and 36% by prey biomass for Eurasian eagle-owls can be comprised by other raptorial birds. The primary raptorial prey taken by Eurasian eagle-owls in Europe are two species: the long-eared owl and the common buzzard. Both are taken in such large numbers that they rank in the top five most regularly hunted bird species in Europe. In Luxembourg, the long-eared owl and common buzzard were the fourth and fifth most regularly hunted prey species. Other high rankings have included the long-eared owl being the fourth most regular prey species in Bavaria and the buzzard being the third most regular prey species in a study from the Czech Republic. While migrating, long-eared owls appear to select areas to move through partially based on whether or not eagle-owls are detected, thus eagle-owls have a very serious influence on the behaviour of this prey. Despite the large numbers taken of both of these, the more scarce eagle-owl does not seem to have a serious deleterious effect on their overall population, especially compared to anthropogenic factors.
Other than these two species, a large share of the raptorial prey for eagle-owls is made up of other owls. Given that all European owls are to some extent nocturnal, they may be encountered and killed upon detection by the Eurasian eagle-owl. In Europe, it has killed every other species of owl, from the tiny pygmy owl and scops owl to the large great grey owl and the snowy owl. The Eurasian eagle-owl is the only raptor that has been known to prey on snowy owl on multiple occasions. However, the threat Eurasian eagle-owls poses to other raptors can be exaggerated. Occasionally, with adequate mammal prey populations, they can nest as close as a few dozen meters of other raptors and never harass them. When nesting in the same groves as the long-legged buzzards ("Buteo rufinus") in southeastern Bulgaria, Eurasian eagle-owls did not predate the buzzards at any point. Long-legged buzzards have been killed however in Kazakhstan. Even in those occasional cases where they pick off one or several raptors, they do not effect the overall population, unless the raptorial prey is already heavily diminished due to some other (often human-based) cause. For example, despite both being a known predator of both, they did not significantly depress numbers of either northern goshawks or tawny owls in southern Finland. One study showed that many raptors engage in spatial avoidance during potential encounters with Eurasian eagle-owls and while the predation by eagle-owls did decrease raptor population densities, they seldom caused declines in breeding success or altered habitat occupancy.