Verreaux's eagle-owl (Bubo lacteus ), also commonly known as the milky eagle owl or giant eagle owl, 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 (26 in) 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 distinguishable 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 composed of 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.
Despite the alternative common name of giant eagle-owl, 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 in addition, 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 (23 to 26 in) in total length. This species has been reported as having an average wingspan of 140 cm (4 ft 7 in), but Mikkola referenced this as the wingspan of a smaller male. The largest known wingspan from a wild female measured nearly 164 cm (5 ft 5 in). 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 (3.560 to 4.409 lb) in males against a body mass of 2,475–3,150 g (5.456–6.945 lb) in females. In one study, 4 males were found to have averaged 1,704 g (3.757 lb) while 6 females averaged 2,625 g (5.787 lb). Another study found 5 males to have averaged approximately 1,700 g (3.7 lb) while five females averaged 2,300 g (5.1 lb). Unusually large sizes have been claimed in captivity with claims that specimens measuring up to 75 cm (30 in) in length and 200 cm (6 ft 7 in) in wingspan 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 (4.9 lb). Among standard measurements, the female is reported to measure from 447 to 490 mm (17.6 to 19.3 in), averaging 465 mm (18.3 in), in wing chord, 230 to 273 mm (9.1 to 10.7 in) in the tail, while the same measurements in the male are from 420 to 490 mm (17 to 19 in), averaging 448 mm (17.6 in), and from 220 to 275 mm (8.7 to 10.8 in) in tail length. In both sexes, the tarsus has measured 73 to 86 mm (2.9 to 3.4 in) and the bill (in a small sample) 51 to 54 mm (2.0 to 2.1 in). 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.
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. As this species avoids primary forests, it is 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 (22 in) 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 (9,800 ft) in elevation, in some central African slopes such as the Eastern Rift mountains. 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-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 Eucalyptus. 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 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 (17,000 acres).
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 (0.18 oz) to ungulates weighing at least 10,000 g (22 lb). 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.
In the heart of their distribution, i.e. east Africa, breeding activity in this species can peak any time from February to September, but can occur nearly any month at the species level. The timing of breeding is said to be correspondent roughly to the regional dry season, so averages earlier in the northern part of the range (before February) and later (July to September) in the southern part of the range such as Kenya and South Africa. In the northern part of the range, breeding season commenced in November in Mali, in November and December in Senegal, December in Equatorial Guinea and January in Nigeria. The monogamous pair is quite stable, most likely mating for life. As in most owls, a courtship display is both to establish mates for a newly mature pair of eagle-owls or to strength pair bonds prior to nesting. Vocalizations during courtship displays consist of relatively rapid and excited calling, hooting and whining. The pair during courtship will bow to one another, flick open their wings and preen each other's feathers, with the male taking the more active part in the courtship ritual. Like all raptorial birds, Verreaux's eagle-owls are strongly territorial. The pair will defend their territory by their song and sometimes (though rarely) through duets. The territories of Verreaux's eagle-owls can range up to 7,000 hectares in size, although average territory sizes are seemingly unknown.
Like great horned owls, but unlike Eurasian eagle-owls, the Verreaux's eagle-owls normally uses old nests built by other birds as their own nests. Usage of a nest site other than those constructed by other birds is considered rarer even than in the horned owl and is viewed as almost exceptional in some parts of this species range. Existent reports of this species building its own nest are certain to be dubious, as no known living owl builds a nest and only a small handful of owl species have been verified adding a small amount of nesting material to an existing surface or nest. They variety of bird nests they use is extreme. Large stick nests in sturdy trees are generally used. In southern Africa, recorded nest heights have ranged from 6 to 25 m (19 ft 8 in to 82 ft 0 in) off the ground. Like other Bubo owls, the large nest of large-bodied accipitrids are often popular for use, due to the often huge size and sturdiness of construction typical in this family, with the nest builders devoting up to four months to their construction. However, perhaps the constructor of nests that most often host Verreaux's eagle-owls are hamerkops (Scopus umbretta ). In everywhere from Mali to South Africa the eagle-owl has been recorded using old nests built by this species. The unusual, massive nest is an enclosed circle of sticks with a side entrance that are often very large relative to the size of the hamerkop, a smallish, compact wading bird. Usually the eagle-owls nest on the flat top of the hamerkop nest rather than the interior which is usually too small for the eagle-owls to enter and this can provide a rather safe structure for the eagle-owl family to call home.
Other nest builders which are popular as hosts are vultures, eagles (at least eight species have built nests used by these eagle-owls), secretarybirds, crows and even much smaller birds such as weavers, which build huge communal nest structures which the eagle-owls then similarly nest on top of. Most nests are already abandoned when the Verreaux's eagle-owl take over it, in large accipitrids for example, many build alternate nests which are not used for years on end. However, if the nest is occupied, the Verreaux's eagle-owl pair readily displaces the occupants and sometimes feeds on the birds in them. Species known to be successfully displaced from their nests have ranged up in size to lappet-faced vultures (Torgos tracheliotos ), which are more than three times heavier on average than the Verreaux's eagle-owl. In some cases, hamerkops have been known to try to defend their nest from the eagle-owls but are usually chased away. Verreaux's eagle-owls have been known to displace other opportunistic nest usurpers such as other owls and falcons in order to take over nest structures for themselves. In one case, a pair of eagle-owls nested on top of a hamerkop nest while the interior of the nest was occupied by Egyptian geese (Alopochen aegyptiacus ), an unusual aggressive species of waterfowl that uses nests built by other species. In rare cases, Verreaux's eagle-owls have been recorded using large, old hollows, the stem of a palm tree or on a very dense tangle of creepers or orchids instead of birds' nests as a nesting site.
On average, the female lays two white eggs, which typically measure 62.6 mm × 51.4 mm (2.46 in × 2.02 in), with a range in height of 58 to 66 mm (2.3 to 2.6 in) and a range in width of 48 to 54 mm (1.9 to 2.1 in). The eggs weigh from 93 to 101.6 g (3.28 to 3.58 oz), the upper weight being the mean mass of the first egg and the lower weight being the mean mass of the second egg. The eggs are reportedly laid at up to 7 day intervals and may take up nearly seven days as well between hatching. Most nest reportedly contain two eggs, but some may contain only one, and no more than two has been recorded in this species. The adult female incubates the eggs for 33 to 39 days, the incubation stage being slightly longer than those of most other eagle-owls, at least the more northern species. On average at hatching, the young weigh about 60 to 70 g (2.1 to 2.5 oz). The weight of the nestling can triple within five days after hatching. Due to the extreme interval between the hatching of the first and the second egg, the older owlet is always considerably larger than the second. As is widely reported in different kinds of raptorial birds, the smaller chick usually dies in the nest. This may be due to starvation upon being outcompeted for food by the older chick or the smaller chick may be being attacked and killed by its older sibling. Usually the smaller chick is gone within two weeks after hatching in this species. In rare cases, both chicks are reared and survive to leave the nest, although there are no known cases of two fledglings resulting from a Verreaux's eagle-owl nest in southern Africa. The young are covered in off-white down from hatching on and the pink eyelids may become apparent within the first week of life. By three weeks of age, the chicks down will thicken and darken to a greyish colour with some barring present. By six weeks, the young eagle-owl will start to somewhat resemble an adult, replete with the blackish brackets on the facial disc of the adult but still being fairly downy, particularly about the head. Only a week later, almost all the down is likely to be moulted.
The mother Verreaux's eagle-owl remains on the nest for nearly the entire incubation period while the male hunts for food for both of them. During the brooding stage, which lasts about 20 days after hatching, the female is still fed by the male, but resumes hunting thereafter. During the incubation and brooding stage, the male usually roosts near the nest during the day while the female continually sits about the nest. After the brooding stage, the female normally takes to a perch within a dozen or so metres of the nest. Both parents may use a favor perch near the nest at which they dismantle prey into pieces that can be more easily consumed by their young, these may be called "plucking" perches where birds are more commonly eaten or "peeling" perches where hedgehogs are the most regular prey. Most dietary studies for the species have been from researching the pellets and skins under such perches. The female is an extremely tight sitter both while incubating and brooding, and may not even be displaced from the nest even if shouted at or the tree is struck. When intruders approach too closely, including other eagle-owls, potential predators and humans, the most common response of the parent Verreaux's eagle-owl is to grunt lowly, often raising its ear-tufts and bill-clapping. Both sexes may engage in distraction displays when the area near the nest is encroached, but it usually the male and most displays occur during nighttime but are possible at any time of day or night. During such displays, the adult will fly lover the ground with drooping wings, or alights and drags its wings and flaps about, often while bill-clacking and calling. Similar injury-feigning distraction displays have been recorded in the Eurasian eagle-owl and smaller owl species but are not known in most other Bubo species. In one case, feral dogs were successfully lured away from a young Verreaux's eagle-owl by its parents’ distraction display after the young bird had fallen to the ground. In rare cases, the parent eagle-owls will attack interlopers. In one such case, a person who picked up a young eagle-owl on the ground was severely injured after both parents attacked him.
On average, the young Verreaux's eagle-owl leaves the nest at around 62–63 days but cannot fly at this point. It may take roughly anywhere from another two weeks to a month after this before the fledgling is a competent flier. After leaving the nest, the fledgling is "remarkably inactive", making a minimum of effort to fly, and usually selecting a roost within a few feet of the nest which it has awkwardly climbed to or will drop to a large bush below the nest. In the nest, the chick will beg for food with a shrill or chittering noise, sometimes bobbing its head or swaying about and transferring its weight between its feet (sometimes called a "hunger dance") and it continues to rely on its parents for food well after leaving the nest. Sometimes after leaving the nest, the young eagle-owls are often mobbed as are adults by other birds of prey and crows during the day, which is often heatedly directed at this species as adult eagle-owls regularly kill these birds at night. The young eagle-owl may dodge to denser branches to avoid being wounded during such attacks. Young Verreaux's eagle-owls may fall to the ground, often as a result of mobbing. If the young bird is discovered on the ground, it may feign death, lying prone with its head lax and its eyes closed. Even if picked up while death-shamming, the young eagle-owl may remain moribund. Upon being left without disturbance after "playing dead", the young Verreaux's eagle-owl will gradually open its eyes and return to a normal state.
It is not until they are about 5 months old do most young Verreaux's eagle-owl show the ability to capture prey for themselves. However, the stage at which the young of this species becomes independent appears to remarkably variable. One ringed 9-month-old moved 24 km (15 mi) away from its nest area and was thus seemingly fully independent. On the other hand, Verreaux's eagle-owls of over half-a-year in age who presumably can fly and hunt on their owl have been seen to linger and continue to beg its parents to be fed into the next breeding season and may even be feed by their father while he is also feeding the mother and a new nestling. In Kenya, when a biologists fed a wild juvenile eagle-owl mole-rats and chicken heads in its nest area, the young eagle-owl apparently became remarkably confiding towards the person. The tendency of young eagle-owls to linger into the next breeding season sometimes results in "family groups" being seen roosting together, a very unusual occurrence for an eagle-owl species. One such group consisted of five birds together, including two parents and three owls from the preceding past three years and apparently the younger eagle-owls even helped bring food for the chick once the egg hatched.
On average, sexual maturity in Verreaux's eagle-owls appears to be attained at three to four years of age. In most cases, a pair of Verreaux's eagle-owl is able to nest annually, however in some cases they may nest only every two to three years, in probable situations of extreme food shortages. Annual mortality appears to be fairly low in this large owl species. Few species have been reported to hunt Verreaux's eagle-owls short of the aforementioned jackal attack, even nests have rarely been seen to be predated, although they may on rare occasions run afoul of some predators such as larger felids with the ability to climb, although such cases are as yet unverified. That young birds usually leave the nest before they can fly would appear to endanger them but the threat and distraction display of parent eagle-owls are apparently often successful. Adult eagle-owls can appear nearly fearless, as they have been reported to stand their ground and engage in threat displays when encountered on or near the ground against much larger animals such as rhinoceroses and lions and in such cases are apparently not approached further by the bigger animals although the eagle-owls could easily be killed by such animals if contact was made. The lifespan in the wild is not known to have been researched, however in captivity the species can live for over 15 years, possibly up to 30 years in some cases.
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 Eswatini, 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.
