Bucorvus leadbeateri (Vigors, 1825)

Species Nomenclature

This species, the southern ground hornbill with scientific name Bucorvus leadbeateri (Vigors, 1825), is a very large bird.

Total Length

Individuals measure 90 to 129 cm (2 ft 11 in to 4 ft 3 in) in total length.

Sex-Specific Weight Range

Females weigh between 2.2 and 4.6 kilograms (4.9 to 10.1 lb), while larger males weigh 3.5 to 6.2 kilograms (7.7 to 13.7 lb).

Average Sampled Weight

The average weight of eight sampled females was 3.34 kg (7.4 lb), and the average weight of eight sampled males was 4.2 kg (9.3 lb).

Weight Comparison to Other Hornbills

On average, these birds are around 35% heavier than any Asian hornbill species.

Wingspan

Their wingspan ranges from 1.2 to 1.8 m (3 ft 11 in to 5 ft 11 in).

Detailed Morphometric Measurements

Additional detailed measurements are: wing chord 49.5 to 61.8 cm (19.5 to 24.3 in), tail 29 to 36 cm (11 to 14 in), tarsus 13 to 15.5 cm (5.1 to 6.1 in), and culmen 16.8 to 22.1 cm (6.6 to 8.7 in).

Size Comparison to Abyssinian Ground Hornbill

Stevenson and Fanshawe report that the related Abyssinian ground hornbill is larger on average, with an average length of 110 cm (43 in) compared to this southern species' average of 102 cm (40 in). However, published maximum weights and standard measurements show the southern species is slightly larger, and average weights for the Abyssinian species have not been recorded.

Plumage and Bare Skin Coloration

Southern ground hornbills have primarily black plumage, with bright red patches of bare skin on the face and throat; juvenile birds have yellow bare skin in these areas instead.

Eyelashes

This species is one of the few birds that have eyelashes, which are thought to keep dust out of the birds' eyes while they forage during the dry season.

Flight Feather Markings

A clear identifying trait is the white tips on the primary flight feathers, which are visible when the bird is in flight.

Beak and Casque Traits

The beak is black, slightly curved, and bears a casque that is more developed in males.

Female Traits

Females are smaller than males, and have violet-blue skin on their throats.

Juvenile Throat Patch Traits

Juveniles under six years old do not have the prominent red throat pouch, and have a duller grey patch in its place.

Distribution Range

Southern ground hornbills have a distribution ranging from northern Namibia and Angola to northern South Africa, and from southern Zimbabwe to Burundi and Kenya.

Habitat Requirements

They require savanna habitat that contains large trees for nesting, and dense short grass for foraging.

Conservation Status

This species is classified as vulnerable, and is now mainly restricted to national reserves and national parks.

Social Group Structure

They live in groups of 5 to 10 individuals made up of adults and juveniles, and neighboring groups often engage in aerial pursuits of one another.

Ecological Role

As apex predators, they are ecologically important.

Diet

They forage on the ground, feeding on reptiles, frogs, snails, insects, and mammals up to the size of hares. They rarely drink.

Western Range Limitation

Their range is limited at its western end by a lack of suitable trees to build nests in.

Vocal Behavior

Groups of southern ground hornbills are highly vocal. They make contact via group chorus calls that can typically be heard from distances of up to 3 kilometres (1.86 mi).

Territory Size

These calls allow each group to maintain its territory, which can be as large as 100 square kilometres (40 sq mi) even in the highest quality habitat.

Cooperative Breeding System

The southern ground hornbill is an obligate cooperative breeder: every breeding pair is always assisted by at least two other birds.

Nest Helper Experience Requirement

Captive experiments have found that birds that do not gain six years of experience as nest helpers cannot breed successfully even when they become breeding adults. This indicates that unaided pairs cannot rear young, and that the skills gained from helping as a juvenile are essential for successfully rearing young as an adult.

Captive Lifespan

In captivity, the maximum recorded lifespan for this species is 70 years.

Wild Lifespan Estimate

It is generally thought that the life expectancy of a bird that survives to fledge is as high as 30 years or more, which is comparable to the lifespan of famously long-lived birds such as the wandering albatross.

Maturity Age

Southern ground hornbills are believed to reach maturity at six to seven years old, but very few individuals begin breeding at this age.

Nest Site Preferences

Nests are almost always deep hollows in very old trees, though there are recorded cases of ground hornbills occasionally nesting on rock faces.

Clutch Traits and Siblicide

One to three eggs are laid at the start of the wet season, but siblicide ensures only one nestling ever fledges.

Egg Characteristics

The eggs measure 73 millimetres (2.87 in) by 56 millimetres (2.20 in), are pure white in color, and have a very rough texture.

Development and Parental Dependence Period

After a 40 to 45-day incubation period and an 85-day fledging period, young birds remain dependent on their parents and helpers for between one and two years, depending on climatic conditions. This dependence period is longer than that of any other bird species.

Breeding Frequency

As a result, southern ground hornbills can normally only breed successfully every third year.

Triennial Breeding Comparison

Triennial breeding is rare in birds; the only other well-documented example is the ornate hawk-eagle of Neotropical rainforests.