Egyptian vulture (Neophron percnopterus) stone throwing

If I told you this is a report on animal behaviour seen by Jane Goodall, I wouldn’t blame you for thinking: chimpanzees. Goodall’s work at Gombe Stream National Park has rightly given her a global audience, which she has used to promote conservation and education through Roots & Shoots and her own institute.

However, her attention to the natural world extends well beyond primates. On Christmas Eve of 1966—just a few years after her ground-breaking 1964 report of chimpanzee tool use—Goodall published another short piece, this time on the vultures she regularly saw during her work in Tanzania.

At the time, she was married to her first husband, nature photographer Hugo van Lawick, and the report is credited to both of them (as Jane van Lawick-Goodall and Hugo van Lawick-Goodall).

Egg assault

The Egyptian vulture was the smallest of the five vulture species that lived around Goodall’s research sites in East Africa. At two locations—one in the Serengeti National Park and one near the famous human ancestor fossil site of Olduvai Gorge—the team watched as individual vultures encountered thick-shelled ostrich eggs.

Like their cousins the white-backed (Gyps africanus) and lappet-faced (Torgos tracheliotos) vultures, these birds could not break into the eggs using the force of their beaks alone—they tried and failed. Unlike their relatives, though, the Egyptian vultures had a backup plan.

Each bird found and picked up a stone from up to 10 yards away. The stones weighed between 100-200g, just a tenth of the weight of the egg itself. Returning to the egg, the bird would raise itself to its full height, with the stone in its beak, then forcefully snap their head down and throw the stone towards the egg.

The vultures only hit the egg around half the time that they tried. But they were persistent, and after 4 to 12 strikes the 2-3mm thick eggshells were cracked. At that point the other vulture species were happy to try and get in on the nutritious meal.

Here’s a short video from the San Diego Zoo Safari Park that shows a (captive) vulture at work:

The van Lawick-Goodalls were not the first to report stone tool use by the Egyptian vulture, or even the direct approach of throwing a stone using the beak. A report from 1857 includes the recollection of Sir James Alexander that, in southern Africa:

a white Egyptian vulture may be seen soaring in mid-air with a stone between his talons. Having carefully surveyed the ground below him, he suddenly lets fall the stone, and then follows it in rapid descent. Let the hunter run to the spot, and he will find a nest of probably a score of [ostrich] eggs, some of them broken by the vulture.

And in the 1870s, military surgeon Arthur Myers was hunting ostrich in the Sudan when he happened upon a now familiar sight:

two visitors in the form of vultures pounced down upon the [ostrich] nest, and, apparently quite satisfied with the certainty of a quiet feast, commenced operations by a personal hunt amongst their own feathers, then a general survey was made of the white objects before them ; and, finally, having retired for a moment, each returned with a stone in its beak, and set to work to hammer a hole through the shell of an egg. But the talents of these experienced old thieves were not allowed to obtain their just reward on this occasion…

Clearly an aerial assault is more likely to succeed when the target is a whole nest of eggs, when even standing directly over a single egg the bird has a 50-50 chance of striking it.

Innate or instructed?

These observations were a solid starting point, but it wasn’t until some 15 years after the van Lawick-Goodall report that researchers more closely tested the vulture’s egg-smashing process. Brian Bertram (Curator of Mammals at London Zoo) and colleagues ran a series of experiments with real, coloured, or fibreglass ‘eggs’ at a number of sites in East Africa.

By controlling the conditions, the scientists were able to see that once a vulture approached an ostrich egg, it was more likely to first touch a stone rather than the egg itself, suggesting that the birds understood the task ahead. The birds then typically spent 10 minutes or more throwing stones at the egg, again actually striking it around half the time.

There was no indication that the vultures were watching or learning from each other, so the research team concluded that the behaviour was an individually expressed, somewhat hard-coded reaction to finding the large eggs.

(These experiments also showed that while the bright white colouring of ostrich eggs made them more susceptible to vulture attacks, it also kept the eggs significantly cooler during the day, offsetting egg predation with flexibility for the mother ostrich in foraging away from the nest.)

A genetic, individual-learning explanation for the Egyptian vulture behaviour is strengthened by the fact that it has now been observed at widely removed locations, from East and South Africa up into Israel and southern Spain. In the latter case, the target was not the eggs of an ostrich, but of cliff-nesting Griffon vultures.

The Spanish example was exactly as described elsewhere: a male Egyptian vulture tried repeatedly and unsuccessfully to break into an egg by throwing stones collected from around the cliff cave, before finally succeeding. While much smaller than ostrich eggs, at around 250g Griffon vulture eggs are still larger than those of most species (in the UK, for example, a medium chicken egg weighs 53-63g).

Overall, the combined observations and experiments suggest a possible pathway by which Egyptian vultures developed their unusual tactic. The birds are known to throw smaller eggs—which they can grasp in their beak—directly onto the ground as a way of opening them. It is a small step from this to the use of stones as the projectile in the same (egg-smashing) context. In both cases, as in much of the tool-assisted animal world, the key is precision and persistence.

Further viewing…

From National Geographic, this video shows a jackal, Egyptian vulture, tawny eagle and lappet-faced vulture successively lining up for an ostrich egg meal. Watch this one with the sound off to focus on the behaviour, or add the commentary and music for full dramatic effect:

Sources: van Lawick-Goodall, H. & J. van Lawick-Goodall (1966) Use of tools by the Egyptian Vulture, Neophron percnopterus. Nature 212: 1468-1469 || Anderson, C. (1857) Lake Ngami; or, Explorations and Discoveries During Four Years’ Wanderings in the Wilds of Southwestern Africa. London, Hurst & Becket. || Myers, A (1876) Life with the Hamran Arabs: an account of a sporting tour of some officers of the guards in the Soudan, during the winter of 1874-5. London, Smith, Elder, & Co. || Thouless, C. et al. (1989) Egyptian Vultures Neophron percnopterus and Ostrich Struthio camelus eggs: the origins of stone-throwing behaviour. Ibis 131: 9-15. || Bertram, B. & A. Burger (1981) Are Ostrich Struthio camelus Eggs the Wrong Colour? Ibis 123: 207-210. || Barcell, M. et al. (2015) Egyptian Vulture (Neophron percnopterus) Uses Stone-Throwing to Break into a Griffon Vulture (Gyps fulvus) Egg. Journal of Raptor Research 49: 521-522.

Main image credit: https://canarianegyptianvulture.com/general-ecology/ || First video credit: San Diego Zoo Safari Park, https://www.youtube.com/watch?v=MWr3iyOOI1I || Second video credit: National Geographic, https://www.youtube.com/watch?v=JfFrnzkZfmI