The five common vultures found in Limpopo are:
~ White-backed vulture
~ Cape vulture
~ Lappet-faced vulture
~ White-headed vulture
~ Hooded vulture
Feeding hierarchy:
The white-backed vultures are the most numerous. They are frantic, noisy feeders, hissing and mobbing one another to get their share of the spoils. They will feed inside a carcass, sheering meat from bones with their powerful bills.
In the case of a closed carcass however, most vultures generally have to await the arrival of the lappet-faced vulture. This “king of vultures” is adept at tearing open the skin of a closed carcass with its huge bill in order to get at the innards.
A lappet-faced vulture is the dominant species at a kill due to its size and power. It will eat tough remains such as skin, tendon, hair and ligament.
The more solitary white-headed vulture generally remains to one side of the feeding activity, taking bits of meat and feeding some distance away.
The hooded vulture feeds on the softer organs like the eyes or intestines of a carcass. It tends to hang around the edge of the feast snapping up scraps, as it is generally pushed aside by the other larger species. Its bill is small and adapted for probing into crevices once the frenzy is over.
Vital role vultures play:
They clean up dead and decaying carcasses, thereby removing centres of disease.
Adaptations to quick feeding:
The crop is a distensible “sack” in front of the oesophagus. Since vultures are scavengers and their food supply is not guaranteed on a daily basis, they have developed the ability to fill their crops in a very short time (about two minutes) with up to 1.4 kg of carrion.
The food remains undigested while in storage. If vultures are unduly disturbed or threatened, they will regurgitate their crop load. The evacuation of the putrid meat lightens the bird so it can escape easily, and also acts as a deterrent to the predator.
Hygiene in vultures:
Due to their messy feeding habits, vultures drink and bathe regularly at waterholes. This extremely social species will gather gregariously at their favourite spots. Sometimes spending an entire afternoon near the waterhole, often with wings spread to sun themselves and restore the shape of ruffled feathers.
Detection of a carcass:
White-backed vultures forage using a grid flight pattern. By circling in an organised manner, one bird can see when another breaks the formation. If an individual spots something and starts to move downwards, its white back offers an obvious beacon for the other birds to follow.
Vultures will also watch for other lower-flying species of vultures (like the white-headed vulture) descending on a kill, as well as scavenging raptors like the tawny and Bateleur eagles.
Vultures have been recorded achieving diving speeds of 120 km/h as they literally fall out of the sky onto a meal. It is this spectacle of vultures dropping quickly out of the sky in an isolated area that indicates the presence of a kill to an observer.
Vultures’ flight:
Vultures use thermals to facilitate low-energy flight. Pockets of rising warm air form when the sun heats the ground during the day, and these thermals provide lift to the enormous birds.
Vultures are equipped with huge wingspans of up to 2.8 m in lappet-faced vultures, which suit this style of flight. Using thermals prevents the necessity to flap these large wings, thereby saving the birds more than three times the energy that would be needed in flapping flight.
Vultures use thermals to gain height in order to look for food, and by moving from one thermal to the next they can survey vast areas easily.
The primary feathers of many birds have distinct indentations near the tip. When the wing is spread the primaries separate into what looks like individual fingertips. It has been suggested that each primary feather acts as a small, independent “winglet” that twists in the air to maintain lift on the wing, allowing the bird to fly slowly without stalling.
Vultures can soar at altitudes of up to 12,000m, covering thousands of kilometres at a gliding speed of about 60km/h, but up to 80km/h. Vultures are restricted to flying during the sunny hours of the day and at night. On overcast days they generally find themselves grounded.
Adaptations necessary for survival:
~ Vultures have strong bills that are adapted to tearing tough flesh. They are curved, have a fingernail texture and continue to grow throughout their lives. In conjunction with this efficient tool, vultures also have serrated, rough tongues for prying smaller bits of meat off carcasses and bones.
~ Vultures have flat feet and their claws are less curved than those of eagles who rely on their talons to hunt. This is because vultures spend a great deal of time on the ground. They would also battle to take the mandatory run-up necessary for them to take off if their talons were more curved.
~ Vultures have excellent eyesight. Some sources state they can see a 6cm object from 1km up in the sky. This makes their eyesight eight times better than humans. A vulture’s eye has two lenses: a fisheye type lens to see the broader landscape and another to magnify objects.
~ Vultures lack feathers on their heads and necks. This is because they are inclined to insert these parts of their bodies directly into carcasses, and if they were covered in feathers they would easily become soiled. Soiled head feathers could cause infection or illness, and preening these areas would also prove difficult.
~ Because of their naked heads and necks, vultures need to have a mechanism to control their temperature as heat exchanges easier through naked skin than through the insulation of feathers. When they are circling kilometres up in the sky, ambient temperatures are cold. For this reason they have a ruff of erectable ring of feathers around the base of the neck. This ruff acts like a scarf. Vultures also pull their necks into their bodies when in flight to prevent heat loss. The naked skin is useful for dissipating heat when on the ground on hot days.
Breeding in vultures:
Vultures are all long-lived species that breed slowly. They can be divided into two main groups with regards to their breeding: Tree nesters (most vultures) and cliff nesters, such as the Cape vulture.
~ Tree nesters such as the white-backed vulture:
Tend to form loose colonies in a suitable habitat, usually where large trees line a watercourse. Their nests are built at the very top of the tallest trees, usually 15 – 25 m above ground. They prefer to nest in thorn trees as these offer protection from predators.
The nest is a sturdy platform of sticks to support the large bodies of both adult and chick. The same site may be reused year after year (up to 15 years in one case).
~ Cliff nesters such as the Cape vulture:
They are extremely social and breed in colonies of between 6 and 100 pairs on cliff faces. This provides them with a good position from which to launch their large, heavy bodies into flight. Their grassy nests are positioned on a ledge, usually where there is some form of overhang.
The structure may vary from a few tufts of grass to elaborate structures decorated with sticks stolen from a neighbour. Nests are also used year after year and eventually the cliff faces become distinctively plastered with droppings.
All vultures are monogamous and territorial around the nest site. In a species that lays more than one egg, incubation begins immediately after the first egg is laid so hatching is therefore asynchronous.
Incubation takes about 56 to 58 days and is performed by both sexes. The altricial chick is fed mostly by regurgitation from the crop onto the nest. In some species the chicks may solicit food by tapping the bill of the parent. Within 45 days it can feed itself from the chewed up food brought back to the nest . The youngster leaves the nest about four months after its first flight.
Inclement weather can increase chick mortality through starvation, because the adults are confined to the nest.
Species specific information:
~ Bearded vultures
Are among the few birds capable of eating bones Their diet consists of 70% bone and marrow. They are able to swallow whole bones of up to 25cm long and sharp ends seem to give them no discomfort.
Larger bones are first dropped from a height of about 60m onto exposed rocky surfaces to break them into smaller pieces. This allows the bird access to the nutritious marrow.
Living in cold mountain habitats, their legs are feathered to the toes for insulation.
The Bearded vulture is the only species to actively search for food by quartering over the ground – gliding or soaring on mountain air currents – and they will cache food in rock cavities when nesting.
In some species, eggs gradually change colour as incubation proceeds. For example, the eggs of the Bearded vulture are white with light, shadow-like markings when laid. As incubation progresses, the iron oxide pigment from the vulture's breast feathers rubs off on the eggs, soon staining them a rich, rusty brown colour.
Bearded vultures salivate profusely over food that they deliver to the chicks, possibly in an attempt to supply the chick with essential digestive enzymes.
~ Egyptian vultures
Are unusual in their ability to make use of tools to access their prized food: nutritious ostrich eggs. They achieve this by throwing or dropping stones onto the eggs in order to break open the thick shell.
The Egyptian vulture is unusual in that its outer two front toes partially webbed.
~ Palm-nut vultures
Has the peculiar reputation of being the only raptor in Southern Africa that feeds mostly on fruit. The flesh of raffia palm fruits provides this bird with a rich, oily and nutritious meal, which it scrapes off using its sharp-edged, broad bill.
Although being predominantly vegetarian, palm-nut vultures also feed on a variety of other foods, including lizards, crabs and fish, which they catch in the same manner as an African fish eagle. They may also cache surplus food in palms.
The chicks of this species are not fed palm-fruit until almost fledged, as up until then they are unable to husk the fruit.
~ Hooded vultures
Are known to follow packs of wild dogs and pick through their droppings in search of tasty morsels.
The face of a hooded vulture is normally a light pink colour, but when stressed, challenged or when breeding, the face will flush a deep pink colour.
Interesting facts:
~ The record holder for the highest flight is the Ruppell’s vulture. One was hit by an aeroplane over the Ivory Coast at an altitude of 11 300m. By comparison, Mt Kilimanjaro, the highest mountain in Africa, reaches a height of 5 895m at its summit.
~ Lack of bone in the diet can lead to osteodystrophy and deformed wings.
~ Females are larger than the males.
~ All vultures have got antibacterial agents in the gut to deal with their diet of often rotten, decomposing food. Some of this is passed out in the faeces, which sometimes gets onto the legs and helps with disinfecting scratches and wounds.
~ Contrary to popular belief, African vultures do not detect carrion by smell. Given the relatively open habitat of their natural range, food is detected by sight, either directly or via observing predators. Smell is used by the vultures from the Americas where the dense tree canopy preludes eyesight as a food procurement tool.
Wingspans of large birds:
~ Lappet-faced vulture Maximum: 2.7 m Average: 2.6 m
~ Verreaux’s eagle Maximum: 2.0 m Average: 1.8 m
~ Martial eagle Maximum: 2.6 m Average: 2.2 m
~ Marabou stork Maximum: 2.9 m Average: 2.6 m
~ Great white pelican Maximum: 3.1 m Average: 2.8 m
Endangered birds:
These “cleaners of the bush” are unfortunately endangered due to the following reasons:
~ Vultures feature prominently in African muti as they are believed to contain powers of premonition or foresight. The possession and ceremonious use of the bird’s skull is believed to transfer its clairvoyant abilities to a person. Possessing the dried foot of a vulture is also believed to bring good luck.
~ Farmers will put out poisoned carcasses to kill problem predators on their property, but will then not remove the carcass afterwards. The vultures will then naturally clean this up and die from the poison.
~ Power lines are often not noticed or seen too late and unfortunately a lot of birds die due to a broken wing or neck, or by electrocution.
Precautionary measures:
Farmers are educated regarding the correct way to get rid of problem predators. Vulture restaurants are placed in strategic areas to try and attract these birds away from surrounding farmlands and to provide them with a safe haven to feed from.
A lot of traditions are being swayed in order to convince native people not to kill vultures.
Power lines are being clearly marked with bright flags, making them more noticeable to birds. And with the help of wildlife centres around the country, injured birds are safely rehabilitated and released back into the wild.
African tales about vultures:
~ When Lions could fly and why vultures scavenge
An ancient Hottentot tale
In the beginning, Lion possessed great magic that gave him the power of flight. All the beasts of the earth and the sky lived in dread of Lion.
Lion was such a ferocious hunter that no animal was safe from his huge appetite. Beside his lair he had built a great graveyard with all the bones from his kills.
Lion was very proud of his prowess as a hunter and he enslaved a pair of Vultures to guard over this monument to his power. Secretly however, Lion feared that the bones in his graveyard would be broken and scattered as this was where he hid his bundle of magical treasures that gave him the gift of flight.
One morning when Lion had flown off on his daily hunting expedition, the Vultures - who were unable to fly in those days - were guarding the vast pile of bones. As the morning wore on, the Vultures grew bored. Suddenly Bullfrog leapt into Lion’s lair and despite the alarmed Vultures' protests, the huge frog started to scatter and break the collection of bones.
“Why should all live in fear of one!” croaked Bullfrog. “If your master is so great, let him come and devour me. I will wait for him at his drinking pool.” And off he hopped.
The Vultures were beside themselves with fear. What would Lion do to them when he saw what was left of his bone display? As they looked dismally over the wreckage, they spotted Lion’s magical bundle. The Vultures opened it and ate up all the contents. To their immense relief they now had the power of flight. To escape from Lion’s wrath, they soared up into the heavens.
Meanwhile Lion had been lying in ambush waiting for his next meal. When some buffalo ventured nearby, Lion tried to soar into the sky and swoop down on the unsuspecting beasts in his usual manner. But without his magical power, Lion was unable to take off. He became very, very angry and ran back to his lair to see what was wrong.
Lion was overcome with rage when he saw the wreckage. Looking up, he spied the Vultures circling high above. Lion roared at them to explain the devastation. The Vultures told Lion of Bullfrog’s actions and the message he had left.
“Come here, you stupid fowl,” ordered Lion, who wanted to teach the Vultures a lesson. The Vultures were not so foolish as to obey however, and rising high on a column of warm air, they circled off over the veld.
Remembering Bullfrog’s message, Lion ran down to the nearby pool. He was going to make someone pay for his lost magic. Seeing Bullfrog sitting on the edge of the pool, Lion crept up to his intended prey. Bullfrog saw Lion’s reflection in the mirror-like pool and leapt out of harm’s way.
Try as he might, Lion could not get close enough to catch Bullfrog, who leapt away effortlessly every time Lion approached. Eventually Lion became exhausted. Worn out beyond anger, he gave up his chase.
Slowly Lion began to plod back to his ruined lair. Then Bullfrog called out, “Ho, King of the Beasts! Now that your magic has gone you must hunt like all other earthbound animals.”
So it has been ever since. Lion can only roam the Earth in search of prey, whereas Vulture can now soar in the skies. But Vulture still fears Lion and only comes to Earth to scavenge carrion when Lion has had his fill.
BIBLIOGRAPHY:
~Emmett, M. (2010) Game Ranger in your Backpack. Briza Publications: Pretoria
Chapter: Birds
Section: Vultures Page 160 – 163
~ Birds: The inside story
Chapter: Mechanisms of flight Page 21
Chapter: Exploring eggs Page 90
Chapter: Bird menus Page 156 – 157
Chapter: The mysteries of migration Page 165
~ When lion could fly and other tales from Africa
When Lion Could Fly and Why Vulture Scavenges Page 92 – 98
~ Beat about the Bush – Birds
Chapter: Did you know? Page 730 – 732
Chapter: Flight and design Page 95, 141 and 151
Chapter: Raptors Page 421
