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Verreaux's Eagle-owl, Milky eagle owl, Giant eagle owl, Bubo lacteus

Verreaux's eagle-owl, also commonly known as the milky eagle owl or giant eagle owl, (Bubo lacteus) is a member of the family Strigidae. This species is widespread in sub-Saharan Africa. A member of the genus Bubo, it is the largest African owl measuring up to 66 cm in total length.

This eagle-owl is a resident primarily of dry, wooded savanna. Verreaux's eagle-owl is mainly grey in color and is at once distinguished from other large owls by its bright pink eyelids, a feature shared with no other owl species in the world.

Verreaux's eagle-owl is a highly opportunistic predator equipped with powerful talons. Just over half of its known diet is comprised by mammals but equal or even greater numbers of birds and even insects may be hunted locally, along with any other appropriately sized prey that is encountered.

This species is considered of Least Concern by IUCN as it occurs over a wide range and has shown some adaptability to human-based habitation alterations and destruction and adaptability to diverse prey when a primary prey species declines in a region.

As a large, highly territorial species of owl, it does however occur at fairly low densities and some regional declines have been reported.

The common name commemorates the French naturalist Jules Verreaux. The type specimen that was later described by Temminck at the Rijksmuseum van Natuurlijke Historie was collected by Verreaux while he was still in his teens.

Range and Habitat
Verreaux's eagle-owl is found through most of sub-Saharan Africa, though it is absent from most of the deep rainforests. The species is found at the highest densities in eastern and southern Africa. Due to the avoidance in this species of primary forests, they are found very spottily in west Africa.

They reach their western distribution in The Gambia, Senegal, Guinea and Sierra Leone. Eastward from those countries, the species is distributed in a narrow transitional zone between the Sahara and rainforests to all the way south to the Central African Republic.

Seemingly isolated populations occur in central Nigeria and central Mali. In south-western Africa, they range up to as far north as the southern parts of the Republic of the Congo and the Democratic Republic of the Congo down to most of Namibia (excluding the coastal regions) and northern South Africa.

In east Africa their distribution is more or less continuous from southern Sudan, Eritrea and inland Somalia down to South Africa as far as the region of the city of Durban.

This species inhabit mainly savanna with scattered trees and thorny vegetation. Verreaux's eagle-owls mainly inhabit rather dry regions, some bordering into arid areas such as semi-desert. In central Mali, for example, near the extreme northwestern limit of the species range, the habitat that hosts these owls averages less than 55 cm of rainfall annually.

They also range into riverine forest adjacent to savanna and small, semi-open woodland surrounded by open country, though they are less likely to inhabit heavily wooded habitats. South African eagle-owls are not infrequent found around floodplains and marshes with floodplains may provide the primary nesting habitat in some areas.

In Uganda, they are largely associated with riparian woodlands. Verreaux's eagle-owl may live at nearly all elevations, from sea-level to near the snow line, at around 3,000 m in elevation, in some central African slopes. However, in general, they only sporadically inhabit rocky areas and so are generally very scarce in mountainous regions.

The bushveld of southern Africa is near ideal habitat for Verreaux's eagle-owl and the species may be found at near peak numbers here. The species was historically rare to absent from the Kalahari desert which makes up the heart of South Africa, but the introduction by man of invasive trees like conifers, eucalyptus and acacias, irrigation areas and prey species closely tied to man has allowed them to spottily occupy this region.

Verreaux's Eagle-owl, Milky eagle owl, Giant eagle owl, Bubo lacteus

Verreaux's Eagle-owl, Milky eagle owl, Giant eagle owl, Bubo lacteus
Range map from - Ornithological Portal is one of those MUST visit pages if you're in to bird watching. You can find just about everything there

Despite the alternate common name of giant eagle-owl, the Verreaux's eagle-owl is not the largest owl or eagle-owl in the world. It is, however, a very large and powerful owl species. This species is both the largest owl found in Africa and the world's largest owl to occur in the tropics.

Among all the world's owls, it is fourth heaviest living owl, after Blakiston's fish owl (Bubo blakistoni), the Eurasian eagle-owl (Bubo bubo) and the tawny fish owl (Bubo flavipes), and is also the fourth longest living owl (measured from the bill to the tip of the tail), after the great gray (Strix nebulosa), Blakiston's fish and Eurasian eagle-owls.

Based on body mass and wing chord length, Verreaux's eagle-owl is about the same size as "medium-sized" races of Eurasian eagle-owl, such as those from Central Asian steppe (B. b. turcomanus) and the Himalayas (B. b. hemachalana), slightly smaller than most northern Eurasian races, considerably smaller than Siberian and Russian eagle-owls, and somewhat larger than the smallest Eurasian eagle-owl subspecies, such as those from the Iberian Peninsula (B. b. hispanus) and the Middle East (B. b. omissus or nikolskii).

Verreaux's eagle-owl ranges from 58 to 66 cm in total length. This species has been reported as having an average wingspan of 140 cm, but Mikkola referenced this as the wingspan of a smaller male. The largest known wingspan from a wild female measured nearly 164 cm.

While female owls are almost always larger than males, Verreaux's eagle-owl stands out as one of the most sexually dimorphic living owl species, some studies showing the female can average 35% heavier than the male.

In comparison, the females of the nominate subspecies of Eurasian eagle-owls and great horned owl (Bubo virginianus) are reported to average approximately 20% and 25% heavier than the males, respectively. The full range of reported body mass in the species ranges from 1,615 to 2,000 g in males against a body mass of 2,475–3,150 g in females.

In one study, 4 males were found to have averaged 1,704 g while 6 females averaged 2,625 g. Another study found 5 males to have averaged approximately 1,700 g while five females averaged 2,300 g. Unusually large sizes have been claimed in captivity with claims that specimens measuring up to 75 cm in length and 200 cm but these are unverified and possibly misreported as these figures match the largest Eurasian eagle-owls.

Males heavier than any in the wild have been verified in captivity to weigh up to 2,200 g. Among standard measurements, the female is reported to measure from 447 to 490 mm, averaging 465 mm, in wing chord, 230 to 273 mm in the tail, while the same measurements in the male are from 420 to 490 mm, averaging 448 mm, and from 220 to 275 mm in tail length. In both sexes, the tarsus has measured 73 to 86 mm and the bill (in a small sample) 51 to 54 mm.

Based on wing chord size compared to body mass and other linear dimensions, the Verreaux's eagle-owl average somewhat larger in the size of its wings relative to its body size than most other eagle-owls, excluding the Asian fish owls which are also seemingly relatively long-winged.

Overall, Verreaux's eagle-owl are a fairly uniform and somewhat pale gray, with light and fine brownish vermiculations on the underside. The back is more solidly light brown with white spots on the shoulder. The oval facial disc is paler, sometimes ranging into a whitish color, than the rest of the front side of the bird with strong black borders bracketing either side.

One other feature that immediately distinguished adult Verreaux's eagle-owls in good light are its pink eyelids. The ecological purpose of their colorful eyelids are not known, however Brown (1965) opined that they replace the colorful yellow to orange eyes of eagle-owls in breeding and territorial displays, since they were very conspicuous in displaying males.

Their eyes are dark-brown in color and like all eagle-owls, they have ear-tufts. The ear tufts are blunter and smaller relative to those of other African eagle-owls. The ear-tufts of this species being relatively subtle of this species can be missed in the field especially if they are held lax.

In appearance, they are quite easily distinguished if seen well. They are much bigger and bulkier than most other co-occurring owls. The only eagle-owl species in range that approaches its size is the Shelley's eagle-owl (Bubo shelleyi), which may (but is not confirmed to) co-exist with the Verreaux's in northern Cameroon and the southern sliver of the Central African Republic most likely in forest edge and mosaics, but that species is a much darker sooty colour overall with broad black bands on the underside.

Shelley's eagle-owl also has considerable different habitat preferences, preferring deep, primary forests, and is much more rarely observed in the wild. The next largest eagle-owl in sub-Saharan Africa is the cape eagle-owl (Bubo capensis).

The individual home ranges, if not habitats, of the Verreaux's and cape eagle-owls may abut in nearly every part of the latter distribution. Even in its largest race (Mackinder's eagle-owl, B. c. mackinderi) the cape eagle-owl is around 30% lighter in body mass on average than the Verreaux's eagle-owl, not to mention it being markedly different in almost all outward characteristics.

Pel's fishing owl (Scotopelia peli), which occurs in west, central and inland southern Africa and may co-exist with the Verreaux's eagle-owl in much of its range (despite favoring wetland and riparian zones surrounded by wooded areas), can attain similar sizes as the Verreaux's eagle-owl but is dramatically different in color (a rather brighter rufous-cinnamon hue) and lacks ear tufts. In combination, the characteristics of their pink eyelids, dark eyes, relatively uniform plumage and extremely large size render the Verreaux's eagle-owl as nearly unmistakable.

The male's song is an exceptionally deep gwok, gwok, gwonk-gwokwokwok gwokwokwok gwonk. The depth and quality of the song makes confusion by sound more likely with a leopard (Panthera pardus) than any other bird. The song is sometimes considered unmistakable.

In Kenya, the voice is considered the second deepest bird call after the southern ground hornbill (Bucorvus leadbeateri). Apparently, the song can carry up to 5 km away on quiet nights. The female's call is similar but higher pitched, as in all owls to some extent because the larger female tends to have a smaller syrinx.

Like most Bubo owls, breeding pairs not infrequently call together but they are not as well-synchronized as the pair duets of cape eagle-owls (Bubo africanus) which are often found in nearby ranges. The alarm calls of both sexes are often a sonorous whok or hook but variable grunting notes and raspy screams also seem to indicate alarm.

Both the female and the young engage in high, piercing calls when begging for food at the nest (at which time the male does the food capture). One other vocalizations recorded include a raspy, drawn-out shrooooo-ooo-eh apparently uttered as a distraction display mainly by the male near the nest.

While sound is important to some degree for inner-species relations and hunting behaviour to all owl species, the Verreaux's eagle-owl appears to have relatively small and uncomplicated ear openings compared to several smaller types of owl, as is typical of most living eagle-owl species, this indicating auditory senses are relatively unimportant in this species compared to vision.

Listen to the Verreaux's eagle-owl

There are no known subspecies in the Verreaux's eagle-owl and there is remarkably little variation in their appearance across their considerable distribution. Reportedly, birds in the southern part of their range appear marginally larger on average but these size differences are quite subtle and may be considered as a mild case of Bergmann's rule.

While genetic research has been untaken for this species, its closest living relative in the genus Bubo is not fully clear. At one time, the Verreaux's eagle-owl was mentioned as an owl with particularly mysterious genetic alliances among living owls. Per Konig & Weick (2008), the species with studied genetic markers found to be most closely related are a dark-eyed species pair of Asian eagle-owls, the spot-bellied (Bubo nipalensis) and barred eagle-owls (Bubo sumatranus) but these are not particularly closely related to the Verreaux's.

Among species with available genomes to study for DNA characteristics, it has been revealed that the fish owls, in particular the brown fish owl (Bubo zeylonensis), is third most closely related species to the Verreaux's. Notably, Konig & Weick did not test the DNA of other African eagle-owls who may bear relation to the Verreaux's eagle-owl based largely on their solid dark brown eyes, namely Fraser's (Bubo poensis), Usambara (Bubo vosseleri), greyish (Bubo cinerascens) and Shelley's eagle-owl, as opposed to other eagle-owls which have yellow to orange irises.

Fraser's and Usambara eagle-owls also have a small amount of bare skin around their eyes but this tends to bluish in color and is not nearly as extensive as the pink seen in Verreaux's. Other large owls native to Africa, the fishing owls, also have uniform dark brownish eyes and are sometimes included with the genus Bubo but how closely related they are to modern eagle-owls is unclear.

Pliocene fossil Bubo owls with clear similarities based on ostelogical characteristics to the modern Verreaux's eagle-owl (most are currently classified as Bubo cf. lacteus) from South Africa and Tanzania, indicate that the Verreaux's eagle-owl descended from slightly smaller ancestors that increased in size as they diversified from related species.

Verreaux's Eagle-owl, Milky eagle owl, Giant eagle owl, Bubo lacteus
An artist's rendering of a Verreaux's eagle-owl from 1838
By Nouveau recueil de planches coloriées d'oiseaux,
Public Domain,

Verreaux's eagle-owls are nocturnal birds and roost by day in trees, with large, shaded horizontal branches of tall, old trees being preferred. In Kenya, the most often used perch trees were Croton megalocarpus and invasive Eucalypts. Elsewhere, Acacia trees may be used habitually.

Despite normally choosing dense foliage to rest in, sometimes they may sit wherever their hunting path ends from the prior night, including relatively exposed perches. They reportedly will sleep rather lightly and will awaken very quickly to defend themselves from attack in daylight hours.

Family groups consisting of breeding pairs and their offspring frequently roost together and may engage in allopreening during this time. Reportedly some family groups include eagle-owls that had hatched up to three years prior, which if accurate is exceptional for any type of large owl species.

During extremely hot days, this species may flutter its throat for cooling purposes and has been known to bathe in rain and shallow water during extreme heat in the middle of the afternoon but usually drinks when possible during nighttime. Each breeding pair of Verreaux's eagle-owl defends a territory and these may be extremely large, ranging in size up to 7,000 ha

Dietary ecology
Verreaux's eagle-owl is considered an avian apex predator, meaning it is at or near the top of the food chain and healthy adults normally have no natural predators. In many known aspects of its hunting behaviour, it is typical of the members of the genus Bubo. This species hunt predominantly in early evening, however they have been observed to swoop on prey during daylight.

The owls usually fly to a different perch from their daytime roost to use as their habitual hunting perch. Verreaux's eagle-owls mainly hunt by gliding down on their prey from a perch. However hunting on the wing has been reported, even of flying insects.

On occasion, they hunt by flying low over a bush to catch prey by surprise or dash on the wing into dense foliage or through forests to catch a galago or other arboreal prey item. They will also sometimes run after prey on the ground, flapping their wings rapidly as they walk, or wade into shallow waters to pin down fish. The wing size of eagle-owls in general limits their flying speed and abilities in the open and so they require perches to execute most of their hunting behaviour.

Even among the Bubo owls, most species of which are known to be highly opportunistic predators with indiscriminating diets, the Verreaux's eagle-owl is a particularly opportunistic predator. While earlier studies characterized great horned owl, one of the most well-studied members of the genus Bubo, has been as hunting whatever random species they first come across, more modern dietary studies have contrarily shown their prey selection is not completely random and that regionally they selected cottontails and hares as prey instead of other foods regardless of prey population trends and become regional specialists on such prey, to such an extent that it predictably causes owl population declines at times when leporid numbers decline.

Furthermore, species-wide, great horned owls may select mammals as prey nearly 88% of the time. In contrast, studies have indicated that for the Verreaux's eagle-owl only around 56% of its diet is comprised by mammals and no single prey type predictably dominates their prey selection by biomass in multiple regions.

To date, more than 100 prey species have been counted for this eagle-owl and, with only about half a dozen comprehensive dietary studies known to have been conducted, this probably only represents a small portion of the total prey selected.

Estimated prey size for the species has ranged from insects weighing less than 5 g to ungulates weighing at least 10,000 g. This is the second broadest size range positively attributed to a single owl species for prey items after the Eurasian eagle-owl and the largest exceptional upper prey-size also after the Eurasian species.

Verreaux's eagle-owl is a seldom-encountered species, occurring at low densities and needing large territories for hunting and breeding purposes. The threats faced by this species are sadly typical of many large birds of prey from around the world. Not infrequently, they are locally rare due to persecution.

The normal cause of persecution is their possible status of predators of small domestic stock, though this is certain to be rare, at least in areas with substantial wild prey populations. An additional threat is the residual effects of pesticides, as poison (usually through rodenticide or poisoned carcasses left out for scavengers such as jackals) consumed through prey may badly affect them.

They may be killed by flying into novel man-made objects, including wires and massive dams along reservoirs. Habitat destruction can also affect them, as they require ample trees with large bird nests in order to take residence in a given area. In some areas, however, they’ve been shown to be able to nest in peri-urban or suburban areas, showing greater adaptability to human based land changes than many other large birds of prey.

In Swaziland, the species is considered Near Threatened and the species has been recommended for threatened status in southern Africa overall. In west Africa and central Africa, the habitat is often marginal for this species, the distribution is sporadic and thus this eagle-owl is only encountered either uncommonly or rarely.

The greatest regional stronghold for Verreaux's eagle-owls is seemingly east Africa, in countries such as Kenya, which may have numbers comparable to pre-colonial times. At the species level, they are widespread and to date are not currently considered to be threatened with extinction.[

Conservation status
Verreaux's Eagle-owl, Milky eagle owl, Giant eagle owl, Bubo lacteus
Least Concern (IUCN 3.1)
IUCN Red List of Threatened Species. Version 2013.2.
International Union for Conservation of Nature. Retrieved 26 November 2013

From Wikipedia, the free encyclopedia
From Wikipedia, the free encyclopedia

Sighted: (Date of first photo that I could use) 19th of November 2014
Location: Xakanaxa, Botswana

Verreaux's Eagle-owl, Milky eagle owl, Giant eagle owl, Bubo lacteus
Verreaux's Eagle-owl - Milky eagle owl - Giant eagle owl, Bubo lacteus

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