THE CAMEL BIRD

The ostrich looks unlike any other bird in Africa. Indeed Its scientific name, Struthio camelus or camel-like bird, compares it to a mammal.

Obvious differences aside, it is not bad imagery. Consider its tall stature, hump-like back, long neck, powerful thighs and big feet. The only bird with two toes on each foot instead of four, a feature it shares with even-toed ungulates or hoofed mammals, it even runs like a camel with its neck and head thrown back.

Above all the ostrich is adapted, like the camel, to withstand desert conditions. When mammals and birds breathe, they exhale air saturated with moisture from their nasal passages and lungs, even if the air they inhaled was dry.

Their systems consequently lose water all the time. Some animals in the Namib are adapted to cool air inside their bodies before they exhale it, a faculty that reduces the amount of water that goes to waste because, at saturation point, cool air contains less moisture than warm air.

Long-snouted animals such as antelope and rodents cool the air in their nasal passages. In the case of the ostrich, a long windpipe helps out, but the adaptation goes even further. Apart from the camel, the ostrich is the only vertebrate in the world known to exhale unsaturated air, with a humidity of some 87%. The shortfall remains in its body.

What this means is that in times of scarcity the ostrich is able to survive on a smaller intake of moisture than it would normally require. When water is available it drinks regularly, but otherwise obtains moisture from its food. It eats grass, succulents, berries, seeds, insects and small reptiles.

In common with other birds in the Namib, the ostrich also regulates its body temperature through specialised behaviour, so as to conserve its body moisture. In the hottest hours it habitually droops its wings to shade its body against the sun, an attitude that simultaneously allows body heat to escape through lightly feathered skin under its wings.

The ostrich also faces the sun to minimise bodily exposure to direct sunlight and raises its back feathers to let body heat out and cooling breezes in.

Such measures suffice only while the air temperature remains below body temperature. On still days when the heat becomes intolerable the ostrich is forced to resort to a risky ploy known as "gular fluttering": it begins to pant rapidly. In consequence it sweats at a time when it actually needs to retain moisture to survive.

Fortunately evaporation saves the day. As the sweat evaporates, the ostrich cools down. It is thereafter able to maintain a body temperature that is nearly normal, around 40°C, even when it is exposed to air temperatures that occasionally rise to 50°C in the desert.

SOUTHERN OSTRICH
(Struthio camelus australis)

The biggest bird in the world

Size: height 2 m; wing 900 mm; tail 490 mm.
Mass: 68,7 kg.
Identification: male mostly black, female brownish grey.
Call: booming, leonine roar.
Habitat: desert and open savannah.
Status: common and secure.

Pure-bred southern African ostriches, once widely distributed and abundant throughout the subcontinent, are now found only in northern Namibia and Botswana. Wild ostriches everywhere else are descended from hybrids crossbred with subspecies from Syria and Arabia for the feather trade.

Ostriches are flightless, but can run at speeds of at least 50-60 km/h, even as chicks. On land only cheetah are faster.

When they are not breeding, ostriches join large flocks, usually about 30-40 strong. On occasion as many as 600 birds are reported to congregate around desert waterholes. Males leave the flock to breed, usually with one female, but up to three in drier years.

A scrape in the ground with a diameter of about 3 m serves as a nest. A typical clutch is made up of 13 eggs, three to eight from each female, with 43 eggs recorded in one clutch.

Eggs are sometimes stolen from other nests and added to the clutch. An average egg weighs 1,4 kg, equal to about 24 chicken eggs. Eggs are sometimes stolen from other nests and added to the clutch. Forty-three were once recorded in a clutch.

The male guards the nest until the clutch is complete and thereafter shares incubation with the senior female. He takes the night shift when the risk of predation is greatest.

The eggs take 39-53 days to hatch. The chicks are able to forage for themselves from the time they hatch, but depend on their parents for protection from predators. In addition parents spread their wings to shade their chicks against the desert sun.


A feathered water-bearer

Unlike the ostrich, the Namaqua sandgrouse needs to drink regularly, as it eats only dry seeds. In a desert where surface water in pans is often brackish, this bird is at a severe disadvantage, as it lacks the necessary glands to rid its system of salt. It is forced to fly as far as 60 km to the nearest source of fresh water, usually a waterhole, where sandgrouse gather in thousands early in the morning.

Sandgrouse chicks are able to scurry around almost from the time they hatch. A brood consists of two or three chicks. They do not require feeding as they largely fend for themselves, but they do rely upon their male parent to ferry water to them. They remain dependent on him for at least six weeks.

When he reaches a distant waterhole he wades into the shallows to quench his thirst and soak his breast feathers. Better than a household sponge, his feathers absorb 20-40ml of water, stowed for the return flight. Upon his return to the chicks they drink from his breast feathers. Each one takes about 3ml of water or almost a third of its body weight.


NAMAQUA SANDGROUSE
(Pterocles namaqua)

Size: length 25 cm.
Mass: 180 g.
Habitat: desert and semi-desert.
Status: common resident, locally nomadic.


Desert specials

Besides the Damara tern on the coast, five birds are endemic to the Namib, where they are confined to distinct ranges. All except one are larks, small and drab. Cryptically coloured to blend with their habitats, typical LBJs or Little Brown Jobs, they are all terrestrial and nest on the ground.


Barlow's lark
(Certhilauda barlowi). 19cm.
Succulent desert south of Lüderitz.

Benguela longbilled lark
(C. benguelensis). 20cm.
Gravel plains north of Omaruru River.

Dune lark
(C. erythrochlamys). 17cm.
Sand sea between Lüderitz and Walvis Bay.

Gray's lark
(Ammomanes grayi). 14cm.
Gravel and interdune plains in coastal desert.

Rüppell's korhaan
(Eupodotis rueppellii). 58cm.
Gravel plains in coastal desert.

Illustrations by Peter Hayman from Sasol - The Larger Illustrated Guide to Birds of Southern Africa (Struik, Cape Town)

Cool heads under a hot sun .......

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