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Episode 338: Bone Eating Bearded Vultures

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The magnificent bearded vulture (image from www.thetimes.co.uk)

When you think of the vulture, you may think of the classic image of a bald headed, large black bird, but the bearded vulture is a significantly more glamorous looking animal. Bearded vultures have a luxurious head of feathers that are often dyed a ruddy red. This vivid color is down to the birds bathing in dust loaded with iron ore. No one knows exactly why they do this, but behavioral scientists hypothesize that it is a status symbol; the more red the their feather are, the more resourceful the bird is, and the better chance it has of mating.

Their majestic looks have made them an important cultural symbol in Iranian mythology, where the bird is known as the Homa, a common motif in poetry, where the bird is featured as a marker of glory, prosperity and happiness. They once ranged more widely than they do today, but are now found in mountainous regions across Southern Europe, Tibet, Africa and the Caucasus.

Bearded Vultures as depicted in Iranian mythology as the symbol of luck and prosperity, the Homa (image from www.theguardian.com)

Bones for breakfast: the diet of the Bearded Vulture

Everyone knows that vultures have somewhat unusual diets, playing a vital role removing carcasses and rotting meat from ecosystems to keep disease down, acting like natures clean up crew. But the bearded vultures take this one step further. Up to 90% of their diet consists of bones.

A bearded vulture getting ready to chow down on a delicious bone dinner (image from www.birdwatchingdaily.com)

Bones may not sound like the most nutritious of meals, but in actual fact there are a lot of important minerals in bones, and more importantly, a very high fat content in the bone marrow. But to get to the nutritious innards of the bones, the vultures have had to learn some very specific behaviour. Famously, bearded vultures will hammer small bones with their beaks and swallow them, but any that are too large are collected and flown to heights as high as 150 metres and dropped onto the craggy ground of their mountainous homes. The bones will shatter and release their delicious innards. This unique behaviour has given the bearded vultures the name Ossifrage, or bone breaker. These are learned behaviours and can take the birds years to perfect the best technique.

A bearded vulture flying to great heights to smash bones (image from Thinnerieux, Yves. www.naturailes.net.)

Once the bones are swallowed by the hungry birds, they pass into a digestive tract with a PH as low as 1, the lowest you can go on the scale. These highly acidic gastric juices, combined with a long intestinal tract, enables the vultures to digest the tough bones and ensures any potentially fatal bacteria are killed off. A large bone can be digested in less than 24 hours with this incredible physiology. They are the only living bird known to specialise in a bone-based diet, but this gives them an incredible advantage. They will rarely find themselves in competition with other birds for carcasses and can hang back from the carnage of a feeding frenzy, waiting for the bones to be stripped clean. This diet also allows them to have their beautiful head of feathers, as they are not digging in the flesh of dead animals, and so don’t need to keep their heads clean. They have also learned to follow large predators like wolves, waiting for a kill, after which they can swoop in and grab the bones.

Although they almost exclusively eat bone, they are known to occasionally attack live prey, and are well known for picking up unfortunate tortoises and dropping them off cliffs for a quick meal. Contrary to damaging rumours, they rarely attack livestock and have never killed a human, although legends told of enormous vultures that could carry off children and farmers lambs, giving them the name Lammergeier, or ‘lamb-vulture.’

Struggling scavengers: uncertain future for vultures

Globally, most species of vulture have faced or are facing an uncertain future. Intentional or unintentional poisoning is one of the biggest issues facing vultures today.  Vultures are highly susceptible to poisoning from lead shot remaining in carcasses and they will absorb lead very quickly thanks to the low PH of their stomachs.  In recent years, vultures have faced enormous problems with a popular veterinary drug, diclofenac. This drug is widely used, especially across India in agriculture, and is highly toxic to vultures, and can even be carried miles away from the drugged carcass, back to their nests. Although bearded vultures rarely eat the poisoned flesh, residues of the drug can be transferred onto the bones and ultimately onto the feathers and beaks of the bearded vultures. In the least few years, despite good work to ban the drug in some parts of the world, the drug is still widely used in South Africa, and of particular concern for bearded vultures, the drug has been approved for use in Spain. Testing of dead nestlings in the last few years has revealed high levels of diclofenac in their tissues.

An information poster warning against the use of Diclofenac (image from tunza.eco-generation.org)

Compounding their mass mortalities from accidental and deliberate poisoning, disturbance of their habitats and collisions with power lines and wind farms are also a major concern. In Spain, a proposed wind farm is causing some concern among conservationists, as radio tagging of vultures revealed that the birds would fly straight into the turbines on their flight paths. In a study examining vultures and their risks from wind farms, researchers found that 8000 vultures have been found dead underneath wind turbines after collisions, with the actual number suggested to be even higher, as its likely at least some of the carcasses will be dragged away by predators. Some vultures are still shot thanks to long held, incorrect beliefs that can carry livestock and even human children off as prey. There is some truth that on occasion they may pick off small, sickly livestock, and they are accidents when a low flying bird will frighten an animal off a cliff. But they certainly have never attacked a human or have the strength to carry off a child!

Increased human presence can also cause vultures to abandon their territories. A study in the French Pyrenees found that with more human activity in an area, from hiking to building developments, there was a vastly increased chance of nest failure in that region. As human access to once impassable mountainous regions increase, vultures are facing increased disturbance, which can be particularly devastating during breeding season. Currently, the bearded vulture is considered one of the most endangered European birds.

Conservation optimism

In the 1970s, ornithologists and scientists realised the precipitous declines the vultures were experiencing, and reintroduction programmes in Europe started. Throughout the Alps and Pyrenees, bearded vultures were steadily reintroduced after they were extirpated throughout the mountains, with feeding stations provided to help support these new populations. Across the world, there are several captive breeding programmes ensuring there are insurance populations.

A bearded vulture being tagged for conservation monitoring projects (image from http://www.africanraptors.org)

The Vulture Conservation Foundation is one of the only charities working solely in the conservation of vulture species. Their aim is to work for the recovery of the four vulture species found in Europe and have developed species action plans to facilitate this. They are also conducting important research into diclofenac with the aim of pressuring government groups to prevent further vulture deaths from this drug. You can check out their amazing work at: Home – Vulture Conservation Foundation (4vultures.org)

Awesome videos!


Arroyo, B. and Razin, M. (2006) ‘Effect of human activities on bearded vulture behaviour and breeding success in the French Pyrenees.’ Biological Conservation

Hernandez, M. and Margalida, A. (2009) ‘Assessing the risk of lead exposure for the conservation of the endangered Pyrenean bearded vulture population.’ Environmental Research

Hirzel, A.H. Posse, B. Oggier, P.A. Crettenand, Y. Glenz, C. and Arlettaz, R. (2004) ‘Ecological requirements of reintroduced species and the implications for release policy: the case of the bearded vulture.’ Journal of Applied Ecology

Margalida, A. Schulze-Hagen, K. Wetterauer, B. Domhan, C, Oliva-Vidal, P. and Wink, M. (2020) ‘What do minerals in the feces of Bearded Vultures reveal about their dietary habits?’ Science of the Total Environment

Margalida, A. Heredia, R. Razin, M. and Hernandez, M. (2006) ‘Sources of variation in mortality of the Bearded Vulture in Europe.’ Bird Conservation International

Negro, J.J. Margalida, A. Hiraldo, F. and Heredia, R. (1999) ‘The function of the cosmetic colouration of bearded vultures: when art imitates life.’ Animal Behaviour

Vignali, S. Lorcher, F, Hegglin, D. Arlettaz, R. and Braunisch, V, (2021) ‘Modelling the habitat selection of the bearded vulture to predict areas of potential conflict with wind energy development in Italy.’


June 14, 2023
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