Cape eagle-owl

Cape eagle-owl
Cape eagle-owl hoots, recorded in Transvaal Province, South Africa
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Strigiformes
Family: Strigidae
Genus: Bubo
Species: B. capensis
Binomial name
Bubo capensis
Smith, 1834

The Cape eagle-owl (Bubo capensis) is a species of owl in the family Strigidae. It is one several large species of the eagle-owl genus, Bubo.

Range

It is found in most of Africa, both north and south of the Sahara, as well as the southwestern Arabian Peninsula.[1] The distribution of the species is widespread and regular, but the owls are absent from the rainforest belt.

Habitat

The Cape eagle-owl is found in a wide variety of habitats, usually mountainous regions and hilly areas with rocks. They are found from sea-level up to the snow line. These owls may also wander into human settlements or even towns, often specifically to predate abundant rock doves.

Description

This is a large owl, though intermediate in size among other large Bubo owls. Its total length ranges from 46 to 61 cm (18 to 24 in). Males weigh from 905 to 1,387 g (1.995 to 3.058 lb) while the larger females range from 1,240 to 1,800 g (2.73 to 3.97 lb). The wing chord measures 34.3–41.8 cm (13.5–16.5 in) while the tail measures 15.5–26.6 cm (6.1–10.5 in). This owl is dark brown above with prominent ear-tufts and yellow or yellowish-orange eyes. It is dark below with the sides of the breast being blotchy brown and the paler chest overlaid with white, black and tawny-fulvous markings, variously. The facial disc is fulvous-brown, with a distinct black or dark brown frame that becomes broader towards the neck. Both the tail and wing feathers are barred with light and dark brown. The toes and tarsi are densely feathered, with the little visible skin being brown above and yellowish below the feet.

The song of the male Cape eagle-owl consists of a powerful, explosive hoot, followed by a faint note: boowh-hu. The female's voice is similar but slightly higher pitched. Pairs on occasion will duet. When approaching a female during courtship, the male will let out a trisyllabic cu-coo-cu while bowing to his mate. Both females and young give a nasal, drawn-out chrrreeh while begging for food at the nest. Females cluck slightly while offering food to their young. When alarmed, both sexes let out a barking wack wack wack....

Subspecies

There are three subspecies: capensis (southern half of southern Africa), mackinderi (southern Kenya south to the northern half of southern Africa), and dilloni (North Africa through Niger and the Arabian Peninsula south to northern Kenya). The distribution of all three is widespread. The nominate race is the smallest-bodied. The race dilloni is generally richer brown in colour, less coarsely marked below and has more distinct barring on the sides and the breast than the nominate. The subspecies mackinderi, which is slightly bigger than the others, is sometimes split as Mackinder's eagle-owl, Bubo mackinderi.[2] The latter subspecies is also a more tawny-brownish colour in plumage.

Behaviour

The Cape eagle-owl is nocturnal, roosting by day among rocks, in sheltered rock ledges or in large rock crevices and caves. They may also roost in trees or even on the ground amongst dense bushes. They have been rarely found roosting in cities like Johannesburg and Pretoria. Often a male and female can be found roosting together, especially just before the breeding season.

The predominant prey for the species is mammals. These can range in size from shrews and small rodents to animals the size of hares which are heavier than the birds themselves. Other important prey can include other birds, up to the size of francolins and hamerkops. Opportunistically, the Cape eagle-owl will supplement its diet with reptiles, frogs, scorpions, crabs and large insects. Mole rats are locally often a favorite prey item and 1 to 3 mole rats can be taken each night during the breeding season. A pair with half-grown chicks requires about 600–750 g (1.32–1.65 lb) per night. Hunts are from prominent perches, with the owl gliding in descending flight after prey and killing them with their powerful talons or bill.

These territorial owls may exist in close proximity where populations are dense, occurring at 2.5 km2 (2,500,000 m2). The male advertises the territory by calling, with duets being rare in this species. During courtship, the male bows and hoots in front of the upright, silent female. The nest may be a shallow scrape on a sheletered rock ledge, in a rock crevice, in a cave or even on the ground underneath a dense bush. More rarely, large stick nests made by other birds or the tops of large bushes are used. Normally the Cape eagle-owl breeds every year, but may breed in alternate years. Usually 2 (rare 1 or 3) white eggs are laid, measuring 5.2–5.7 cm (2.0–2.2 in) x 4.3–4.8 cm (1.7–1.9 in) and weighing 62 g (2.2 oz), at 2 day intervals. The female incubates for 34 to 38 days, while the male feeds her. The young hatch at intervals of up to 4 days. New hatchlings weigh 42–51 g (1.5–1.8 oz), then weigh 500 g (1.1 lb) at 20 days and are nearly adult size by 40 days. The female broods the chicks, feeding them with small piece of meat brought by the males. At 11–13 days old, the chicks sprout buff down from the mesoptile plumage. Although at times of plenty, all chicks may survive, usually the second, smaller chick dies from starvation. By 17 days, the female occasionally leaves the nest but still roosts near the young. By 3 to 4 weeks, the mother stops coming to the nest but still roosts with the young. If the nesting site permits, the young start walking away from the nest at around 45 days old and can fly well by 70–77 days. The young are cared for a total of 6 months and reach sexual maturity the following year.

Status

The Cape eagle-owl is classified as being of least concern by the IUCN, since its range is fairly large and populations appear to be stable.[1] They are common in areas such as the Mau Plateau in Kenya, though are locally rare to absent in other parts of their range. Around 50–60% of breeding attempts are successful. Predation of nests (especially ground nests) is common as are roadkills and casualties due to power-wires and barbed wire. The use of pesticides to kill rodents may ultimately effect the species.

References

  1. 1 2 3 BirdLife International (2012). "Bubo capensis". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013.
  2. ↑ Weick, Friedhelm (2006), Owls (Strigiformes): Annotated and Illustrated Checklist, Springer, pp. 110–111, ISBN 978-3-540-35234-1
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