How do vultures make and lay eggs?

Inside a Cape Vulture's egg
Inside a Cape Vulture’s egg

Have you ever wondered how a vulture makes and lays eggs?  We did and searched to find the answer, so that we can better understand how their bodies work and ensure that our captive breeding programme for population supplementation has the highest success rate possible.  Eggs it turns out are proof of nature’s mastery of engineering.

Reproductive System

It has been noted during post mortems conducted on vultures that have had to be euthanaised, that the female vultures have a very small right ovary.  Like us they do have two ovaries present in their bodies, unlike us the left is larger and fully functional, while the right is smaller and inactive, rather like in chickens.  The theory is that if anything happens to the left ovary then the right ovary could become active to continue the ability to breed.  Sadly there is still a huge amount of information that we just don’t know about vultures, which is why VulPro works so hard not only to conserve them but to research and understand them too.

The video featured below is wonderful and shows clearly how the egg laying process works in chickens.  This gives a very good idea of how it works in vultures too.

All about eggs! – How is the egg formed?

The egg starts its journey as the yolk (oocyte), which is produced by the female vulture in her ovary during ovulation. Each yolk (ovum) is enclosed in a thin-walled sac, or follicle, attached to the ovary. This sac is richly supplied with blood. The mature yolk is released when the sac ruptures, and enters the funnel of the left oviduct.   Fertilised or not the yolk travels through the oviduct which is a long spiralling tube.  It is in the oviduct that the yolk can be fertilised if a mating was successful. As the yolk’s journey progresses down the oviduct into the section called the magnus; it is covered with the vitelline membrane, structural fibres and layers of the albumen (egg white).  The egg continues its journey through the oviduct, spinning as it goes (a bit like a bullet travelling down the barrel of a gun).  This spinning movement twists the structural fibres into the rope like fibres that we call the chalazae. There are two chalazae on opposite ends of the egg that hold the yolk in place.

The shell is not created by the chicken but actually formed by the egg itself, in the lower part of the oviduct just before the egg is laid.  The shell is made of calcite (a form of calcium carbonate).  It is the membrane surrounding the egg that has evenly spaced areas where columns of calcite form as they develop these columns form side by side creating a shell.

Cape Vulture egg being weighed
Cape Vulture egg being weighed

A vulture’s egg weighs in the region of around 260g compared to 33 – 75g for a chicken’s egg.   When you look at an egg you will see that it has a broader rounded end and a narrower pointy end.  As the egg travels down the oviduct, it moves pointy end first.  Just before an egg is laid the egg turns around so that the rounded broader end faces downwards – logic says that this is because the broader rounded end provides a softer landing surface to prevent the egg from cracking or breaking as it lands in the nest.

We also had a very interesting case with an African White-backed Vulture who became egg bound and required assistance to try and save her egg as well as her life.  Her egg was presented narrow pointy side first and ended up jammed, sadly we couldn’t remove the egg without cracking it.

African White-backed Vulture - Egg bound (incorrect presentation of egg)
African White-backed Vulture – Egg bound (incorrect presentation of egg)


Natural Protection

The rounded end of the egg contains the air sac, once an incubating vulture chick’s lungs are developed enough; they use the air in the air sac to breathe prior to hatching.  When eggs are laid they have a natural sheen on them that helps to prevent air and bacteria from entering the egg.  Protecting and preserving the sheen is one of the reasons that eggs should not be washed if they are going to be stored.

Eggshells are porous which means that air and bacteria can enter the egg through the pores in the eggshell.  The albumen or egg white provides a layer of protection for the yolk which is situated more or less in the middle of the egg.   The egg white is very alkaline which slows down bacterial growth unlike the nutrient rich yolk which is a bacteria’s paradise.  This is why when we talk about storing chicken’s eggs for us to eat, they should be stored at a 45°angle, pointy side down, this keeps the air sac at the top of the egg and furthest away from the yolk.

Interesting Facts:

A female vulture can fly when she is carrying an egg.


Video Link:

Lead toxicity – Dangerous to humans and vultures alike!

Vultures feeding - Vulture restaurant @ VulPro - Photo Mandy Schrode
Vultures feeding – Vulture restaurant @ VulPro – Photo Mandy Schroder

Understanding Lead Poisoning

All Birds of Prey, especially long lived, slow breeding species such as vultures, are at risk of lead poisoning.   Vultures and other animals are exposed to lead shards when feeding on animals that have been killed by lead bullets as well as from the entrails left behind by hunters.  It also highlights the responsibilities of places housing raptors such as vultures to ensure that their enclosures are lead free, this applies to lead free paint and a lead free water supply, a problem in many older facilities where water was routinely piped in lead pipes, soil needs to be lead free and vegetation supplied needs to be lead free too, another factor to consider here are the emissions from lead based petrol.

Interesting Fact

New world vultures such as the Californian Condor are far more susceptible to lead poisoning than our Old World Vultures

In large quantities lead is detrimental to the nervous and reproductive systems

Radiographs from a Cape Vulture chick showing severe osteodystrophy caused by lead toxicity
Radiographs from a Cape Vulture chick showing severe osteodystrophy caused by lead toxicity

of vultures.  A vulture with lead poisoning will show weakness and anorexia, the most dangerous symptoms are not easily detectable until serious damage has occurred.  The Cape Vulture experiences osteodystrophy  (softening and degeneration of the bones) and reduced reproductive success. For a slow breeding species like the Cape Vulture this has a huge impact on the species population numbers, as well as the number of vultures who experience poor bone development resulting in ongoing fractures and ultimately death.

We need to educate farmers, landowners and hunters regarding the effect and dangers of lead toxicity on our wildlife and endangered species such as vultures. If carcasses killed using lead bullets are to be left accessible to vultures, bullets and any shards of lead need be removed. Hunters also need to be educated about using environmentally safe, non-fragmenting copper bullets.

Why is Lead such an issue?

  • Lead bullets are designed to shatter or fragment on entry, this leaves small particles scattered throughout the carcass which scavengers ingest.
  • Lead toxicity in the Californian Condor has also proven to lead to lead accumulation in bone over time
  • Vultures are a long lived, slow breeding species. This means that their recovery from population drops is too slow.
  • Vultures scavenge communally, meaning that a single contaminated carcass can poison several vultures.

Understand the Role of Hunting

Every healthy ecosystem needs to be managed by checks and balances; hunting is a natural part of the environment that predators rely on for survival.  Man may no longer need to hunt to survive but he is necessary for keeping populations under control thanks to our impact on the environment.  The scraps that hunters leave behind help to feed many scavengers and hungry predators, because of this we need to encourage hunters to use non-lead bullets.  The effect of lead is not just seen on our vultures but affects our other wildlife as well.

Scary Fact

A terrifying fact is that more than 500 scientific studies published since 1898 have documented that worldwide, 134 species of wildlife are negatively affected by lead ammunition.

Human Health Concerns

South Africa is a country of meat lovers and game meat is a roaring trade whether it is biltong or a venison roast, studies worldwide are increasingly showing that lead fragments can also be found in wild game meat processed for human consumption.  Added to this we are exposed to lead fuel emissions, plants and vegetables that have absorbed lead and lead found in water carried in old lead pipes.

Lead toxicity in humans can have horrific consequences over time, developmental abnormalities in newborns and children, and may even result in death.  In adults the symptoms range from high blood pressure and joint pain to a host of other health issues in between.

The World Health Organisation lists the key facts about lead poisoning as:

  • Lead is a cumulative toxicant that affects multiple body systems and is particularly harmful to young children.
  • Childhood lead exposure is estimated to contribute to about 600 000 new cases of children developing intellectual disabilities every year.
  • Lead exposure is estimated to account for 143 000 deaths per year with the highest burden in developing regions.
  • Lead exposure is estimated to account for 4% of the global burden of ischaemic heart disease and 5% of the global burden of stroke.
  • About one half of the burden of disease from lead occurs in the WHO South-East Asia Region, with about one-fifth each in the WHO Western Pacific and Eastern Mediterranean Regions.
  • Lead in the body is distributed to the brain, liver, kidney and bones. It is stored in the teeth and bones, where it accumulates over time. Human exposure is usually assessed through the measurement of lead in blood.
  • There is no known level of lead exposure that is considered safe. Lead poisoning is entirely preventable.

Hunting using Non Lead Bullets

Lead bullets have been used because their design allows a for quick clean kill. The rapid expansion of the bullet provides the hydrostatic shock needed to give a quick kill but also results in lead fragmentation.

The modern lead free bullets still allow for the rapid expansion resulting in a clean kill, but don’t result in the fragmentation that is so dangerous for humans and wildlife alike.  For those who do love to hunt, there are a number of websites which offer advice and guidance on the use of non lead bullets.  They also host interesting and yet terrifying information showing just how far lead fragments travel in the body.


Link for hunting with non lead bullets:

How do vultures fly so high and survive?

Cape Vulture - Vulture Restaurant @ VulPro - Photo Copyright Mandy Schrode
Cape Vulture – Vulture Restaurant @ VulPro – Photo Copyright Mandy Schroder

Vultures are amazing birds that can soar and glide for great distances, they have adapted over time to allow them to fly at great altitudes where oxygen is in short supply.

Mechanics of flight

Whether you are flying in an airplane or a vulture gliding across the sky, flying remains a balance between two sets of forces – “lift and weight” and “thrust and drag”. Lift is created by the flow of air over the wings and weight is created as a result of gravity.  Vulture’s wings are concave on their underside and convex on the upper surface, because of this shape the air that travels over the wing has a greater distance to travel resulting in it speeding up, this causes the pressure to drop (this is because the same amount of air is exerting its pressure over a larger area above the wing than below it.  This creates “lift” or sucks the wing up.

At the same time the exact opposite is happening on the underside of the wing, the air slows down, creates more pressure and “pushes” the wing up. This push and pull effect happens the most along the thin trailing (back) edge of the wing and causes a spiralling vortex (whirling mass) of air disturbance at the wing tip which increases the drag.

Gliding & Soaring

Vultures are masters at soaring and gliding, hanging in the air without having to flap their wings.   Their wings are large, ideal for gliding, but very hard work to flap for flight.  Soaring means that vultures don’t lose height and often climb higher in altitude by using no energy of their own – instead using the thermals (rising masses of warm air), obstruction currents which are produced when wind currents hit mountains or tall buildings cause the air to rise lifting vultures to higher altitudes.  Vultures have large, broad wings and their proportion of bodyweight to wing size is low, making them the perfect gliders and soarers.

Brain straining fact:

 “Aerodynamic properties are measured by aspect ratio, which is the ratio of wing length divided by wing breadth. Long wings are better for gliding but harder to flap quickly and are therefore not much good at quick acceleration.  Wing loading is the relationship between total body-mass measured in grams versus total wing area measured in square centimetres.” (

Feathers for Temperatures

Cape Vulture - back feathers up close
Cape Vulture – back feathers up close

At the higher altitudes, temperatures can drop to -60°C, to survive this high fliers have developed a layer of soft down feathers that act as insulation – exactly why we use down duvets in winter.  Special feathers called “Contour feathers” cover the body, streamlining it and effectively reduce the drag.  “Remiges” are primary feathers, found on the wings they help with flight and provide wing shape.  “Rectrices” are tail feathers which stretch sideways making the tail work like a rudder for turning and balancing.

Bullet shaped bodies

The vulture’s body shape is suited to flight with the centre of gravity being situated slightly below and behind the wings, the placement of the centre of gravity helps with better balance in flight.  Added to the position of the centre of gravity a large number of the organs and large muscles are found near the centre of gravity.


A vulture’s wings are the equivalent of our forelimbs or arms, they attach to the body closer to the vulture’s centre of gravity.  The “hand” bones are small, fused, flattened and are specially adapted to manipulate the flight feathers and “feel” the air for riding thermals.

Bare Bones

Pneumatization means “The development of air cells or cavities, such as those of the mastoid and ethmoidal bones.” (

Evolution has allowed vultures to adapt for flying by reducing their weight by:

  • Fusion of some bones
  • Removal of unnecessary ones
  • Pneumatisation of bones
  • Large bones are often connected to respiratory system air sacs.

To ensure that their bones remain strong they have internal truss like reinforcing.  Fusion of certain bones lightens the skeleton while increasing its strength.   An important adaptation is the fusion of the caudal (tail) bones into what is called a pygostyle(the Pope’s Nose on a chicken).  This pygostyle supports the tail feathers, with the tail working as a rudder it needs to remain strong.

Vultures also have no teeth, having evolved with a beak which is lighter.  Bird’s ribs are stronger than ours as they have hooked boney extensions (uncinate processes) which overlap with the rib behind them providing extra strength and stability.

A vulture’s skull is made up thin hollow bones making it very light

Height Records

  • Andean Condor 15 000feet
  • White Stork 16 000 feet
  • Bar-tailed Godwit – 20000 feet
  • Mallard – 21000 feet
  • Bearded Vulture – 24000 feet
  • Alpine Chough – 26500 feet
  • Whooper Swan – 27000 feet
  • Bar-headed Goose – 29000 feet
  • Common Crane – 33000 feet
  • Ruppell’s Griffon Vulture – 37000 feet [11,274 m when a Ruppell’s griffo collided into a commercial airline over western Africa (Martin, 1987)]


Respiratory System

High Flyers counteract the reduced oxygen levels by having an amazing lung respiratory system, which uses the smallest amount of oxygen available to its full effect.  So why do vultures fly so high… to use the natural jet streams found at higher altitudes, allowing them to cover massive distances with little effort.

A vulture’s respiratory system is proportionately larger than ours is.  Their lungs are smaller and less flexible than ours are as well as being connected with a network of large thin walled air sacs in the body.  The air sacs are also interconnected with the air spaces in the bones.  Vultures like most birds have a unidirectional method of breathing, this means that fully oxygenated air is always entering the lungs unlike us where we breathe into and out of our lungs, resulting in fresh air mixing with old air.

Respiration-bird-mammal-insectAnimated gif used with permission of and created by Eleanor Lutz (Eleanor’s website:

Heart & Blood

A vulture’s heart is large and powerful as well as being similar to ours by having 4 chambers.  The Bird’s heart is large, powerful, four-chambered and of the same basic design as that of a mammal. The vulture’s circulatory system is like its respiratory system in that the blood is separated into oxygenated and de-oxygenated, making them well equipped to handle their high flying.  They also have higher blood pressure and blood glucose levels than ours.


Birds have high metabolism and are able to generate and regulate their body temperature (endothermy) for rapid availability of power and maintenance of high body temp at cold altitudes.

Sabi Sabi Wild Facts: Vultures

How do vultures learn to fly?

Cape Vulture chick flapping wings on the nest ledge
Cape Vulture chick flapping wings on the nest ledge

Vultures are big heavy birds that can look quite comical with their funny hopping walk on the ground.   Watch them in the air and it is a completely different picture, graceful, powerful and free they can soar and glide for hours as they ride the thermals searching for food.  Vultures are specially built to soar beautifully, their wings are huge and they have short tails.

The Cape Vulture nests on rocky ledges and cliff faces in a nest made of grass and sticks.  Vulture chicks are often seen practicing flapping their wings while they are on their nest ledges, sometimes flapping so hard that they lift off the ledge a little bit.  When the wind picks up they open their wings to feel the wind through them – this may be a way of learning how to feel and use the wind when they do fly.

Watching vultures coming in to land at VulPro’s restaurant, you start to appreciate what skilled flyers they are.  Watching their wing feathers flare on one side while the curve the wing more on the other to change direction, slowing right down to check their specific landing spot or changing their minds and soaring off again.

Dating on the Fly

A vulture’s version of dating is soaring around each other in the sky, with the male behaving like a fighter pilot, showing off his skills by almost touching the female’s wing tip as he flies.  Vultures are very sociable in their colonies, but when it comes to pairing up and breeding, they mate for life.


Vulture chicks fledge, or take their first flight, at around 140 days after hatching.  They are the same size as their parents but not quite as heavy and they have their full feathers just their colouring is different showing their youth.

Nature vs Nurture

Birds are born with the instinct to fly; they do still have to learn the mechanics of it though, a little like our parents helping us learn to walk.

It is thought that the vulture chicks build their bravery, strength and muscle development with their wing flapping on the ledge to be able to take the first leap.  Relatively speaking, it appears that the leap and subsequent gliding is easy for them, the difficulty and challenge occurs when they need to get back onto the cliff.  This takes more, skill maneuverability and stamina, and is often the reason that we find so many grounded young fledglings, a bit like us learning to drive, they have the forwards part down pat, but the parking skills are sadly lacking.

There are also reports of parents who” kick” the fledgling out of the nest; this may involve stopping feeding the chick or not allowing the chick to roost on their ledge as well as the literal kick out the nest.  This is nature’s way of making sure that the parents are able to hatch their next egg and raise the next chick. Only with practice do they learn the ropes and develop the muscles necessary to flap their wings to their fullest potential.

How do vultures feed their babies?

Vultures don’t have the strongest legs and feet and they are big heavy birds.  They couldn’t carry meat back to their nests for their chicks held in their talons like eagles do, so how do they feed them?

Clever crops

Vultures like other birds have a crop, the crop is a pouch near the throat and it is a part of their digestive tract, which serves as a storage compartment.  The crop is used to hold extra food, when the tummy is full, a bit like how your mom carries food home in shopping bags for the family.

Yolks aside!

Chicks in the wild hatch from the egg over a number of days (yes it’s a really long time), while they are working to get out of the egg, it is the yolk that feeds them.  The chicks have a yolk sac which sits outside their bodies that they are attached to.  By the time that they are fully hatched, the yolk sac has been fully absorbed into their body.  Once they finally leave the shell they are hungry and need to be fed.  Cape vulture adults have been seen to “drool” into the chick’s mouths within their first day of leaving the shell.  It is thought that this is just saliva (it needs more research) – we think that it is probably good for hydration and possibly other minerals that help the chick do well in their huge change to living in the big wide world.  Although we think that the saliva helps the chicks, they also need solid food immediately after hatching.

Food is eaten at the carcass by the parent bird and is then carried home for the chick in their crop, once back at the nest the food that is held in the crop is “unpacked” (rather like your mom putting her shopping away) and the chick feeds.

Dem Bones

Vultures are heavy birds on relatively thin short legs, their bones need to be really strong for them to stay healthy, fit and to survive.  To do this, they need enough calcium and vitamin D in their diets.  Vultures get calcium from bone chips and fragments from the carcasses that they feed on; to start with these chips are in the regurgitated food that the parents feed their chick. Once the chicks are older, the parents will often give them larger bone chips separately to their food; adult vultures have been seen to pick up large bone chips out of the nest and “offer” them to the chicks.  Vitamin D is absorbed through the skin from the sun and is used along with calcium in the body to help develop good strong bones.

Flying the Nest

To “fledge” means- “(of a young bird) develop wing feathers that are large enough for flight.”

Cape vulture chicks start to fledge when they are around 4 and a half months old (140 days), like us though, they do need to test their wings.  Some vultures are more confident and outgoing and will leave their parents earlier than those chicks that are a little more nervous of the big world that waits for them.

Like us when we leave home, young fledglings have to learn how to find food and to cope with getting their share at a carcass when there are so many vultures competing for food.  Mostly the young fledglings will have their adventures but still return to the nest ledge where their parents will still feed them, this can happen for a few months until eventually the parents get fed up with their chick and start to kick the chick out of the nest, this also happens because the parents have to get ready for the next egg and chick that they will have.

VulPro has a very busy time in November and December because this is when we end up rescuing lots of young fledglings who have gotten themselves into trouble because of their inexperience and the fact that they often don’t get enough food.   A vulture that doesn’t get enough to eat starts to burn their fat reserves to survive, when these reserves are finished they start to metabolise their muscle in order to survive, this leaves them too weak to fly and compete for food and ultimately leads to their death. VulPro collects the fledglings and we help them get stronger in our “nursery enclosure”.  Here they learn to compete for food in a slightly easier environment.  Once the fledglings have the necessary skills and strength to survive, VulPro tags and releases them back to the wild.

How do vultures cope with and kill deadly germs?

Cape Vultures feeding at VulPro's Vulture Restaurant
Cape Vultures feeding at VulPro’s Vulture Restaurant

Humans get food poisoning so easily and have to be so careful with our food, yet vultures eat rotting meat from carcasses and are absolutely fine, how do they do it?

The simple answer is that vultures stomachs are filled with serious or noxious bacteria that are stronger than the bad bacteria that they swallow whilst eating.  Their stomach acid is also very strong which helps them to break down the bacteria on their food as well.

Strange Fact:

A vulture’s stomach acid is 10 to 100 times stronger than human stomach acid, making the stomach itself is a very harsh environment for bacteria to survive in.

This means that vultures in effect have turbo tummies that can kill off diseases that are a real threat to humans and animals alike.  Diseases such as Anthrax, Botulism and Foot and Mouth; vultures can even deal with Leprosy.

The vulture’s stomach has mostly two bacteria in it and strangely both are known as poisons by humans:

  • Fusobacteria, which can cause blood infections
  • Clostridium, which produces deadly botulism toxins

Studies conducted on alligators (also carrion eaters) showed that they also have high levels of Fusobacteria and Clostridium, this suggests that these scavengers have developed this microbiome (the bacteria and environment in their stomach and intestines) allowing them to thrive on what would kill other animals and people.

This is one of the reasons that vulture restaurants are so important for farmers, especially in the rural communities where a disease outbreak such as foot and mouth could ruin farmers, leaving them with nothing.  Vulture restaurants allow farmers to safely and quickly get rid of their carcasses while supporting and helping to save many endangered vulture species.

Below is a short video of hungry wild vultures, trying to get into one of our enclosures to gain access to food.  VulPro’s vulture restaurants sees hundreds of vultures and marabou storks visiting it everyday benefiting from the regular supply of safe food.