The bone-breaking Lammergeier: a truly awesome avian

Number 9 on my top ten animal countdown goes to the Lammergeier, a denizen of the high mountains in Europe, Africa, and the Himalayan region. German for “lamb vulture,” this enormous bird was so named for the belief that it preyed on domesticated animals. With upwards of a nine-foot wingspan, it’s not hard to imagine a Lammergeier flying off with even a small child, and in fact, they were once hunted in large numbers for this very fear. Of course, like in so many cases, our fears turned out to be baseless. We now know this silent giant, otherwise known as the Bearded Vulture, to be relatively harmless.

Despite the eagle-esque build, the Lammergeier, like all vultures, is mainly a scavenger. It belongs to a group of so-called “Old World” vultures, which are part of the same taxonomic family as hawks, eagles, and the other diurnal birds of prey. “New World” vultures, like the Turkey Vultures of America, have long been thought to comprise their own independent branch of the bird family tree. One of the main points in support of this is a stark contrast in how each group finds food. Old World vultures like the Lammergeier rely exclusively on sight, while their New World counterparts have evolved a keen sense of smell, something quite rare among birds. However, a recent and influential paper in the Journal Science has reshuffled a number of avian lineages in light DNA analyses, which included reclassifying the New World vultures into the same family as their raptor brethren, Accipitridae.

Just how far back vulture ancestry splits is still up for debate, but the apparent visual similarities between the two groups may still prove superficial, a result of a convergent evolution. This is the tendency for a set of advantageous traits to evolve independently in multiple lineages. For vultures of either world, having a sparsely feathered, or bald, head is a must to minimize contamination when tearing flesh from carcasses. The Lammergeier is a bit unusual among the vultures in that it does have a fair amount of cranial feathering. It is as if it evolved toward baldness and then came back the other way. Given what it has come to eat, this notion may not be too farfetched. When a carcass turns up, the Lammergeier is almost always last on the scene. It’s an animal that has dispensed with interspecies squabbles because it’s after something few others can eat: bones.

The Lammergeier dines almost exclusively on osseous matter. 90% or more of its diet is bone. Although many animals will consume marrow, it is incredibly rare in the animal kingdom to have such a huge dependence on bones alone. To my knowledge, only a marine worm that feeds on whale carcasses, the Osedax, shares

An unusually white, perhaps albino, adult. Apparently named Victor, the anklet visible in this shot means he's part of a population study.

this trait. To accomplish such an incredible level of specialty, the Lammergeier has two very distinctive traits. The first is a stomach every bit as acidic as battery acid, which allows it to extract nutrients from not just the marrow but also the bone itself.

The second is one of the cleverest bird-brained behaviors out there. Though it can swallow morsels up to the size of a lamb’s femur, the Bearded Vulture often encounters meals too big to swallow. To solve this problem, it has learned to break large bones into smaller pieces by dashing them on rocks from high in the air. Like dropping bombs from jet, this technique requires an incredible level of precision, and it can take young birds up to seven years of practice to master. Such a novel approach has earned the Lammergeier my favorite of its aliases: Ossifrage, or “bone breaker”. But that’s not the only thing it drops. The Ossifrage has also been know use its bone-breaking technique to crack into the shells of live tortoises. Aeschylus, the Greek playwright, was reportedly killed in 456 BC when an eagle mistook his bald head for a rock and dropped a tortoise on it. Although Golden Eagles have also been known to exhibit this behavior, it is perhaps a tad more likely that a Lammergeier did the job (if indeed the unlikely story is true).

Dropping a bone onto rocks below.

Sky burial site in Batang, Tibet.

The Bearded Vulture is also notable for an interesting relationship it has with the people of Tibet. In the high alpine mountains, timber is scarce and the soil is thin above the rock. This makes it very difficult to bury or cremate the dead, so Tibetan Buddhists have adopted a more unusual approach – the sky burial. First described in the 8th century Tibetan Book of the Dead, this is the practice of allowing vultures and other animals to decompose human corpses. And with the dryness of the mountain air, it would take a very long time indeed for bones to disappear if not for the Lammergeier. (I decided against a more graphic image for this paragraph – have a look at a Google image search on “sky burial” if you’re not too squeamish.) Though this may seem a strange from a Western perspective, it is truly a practical solution for funerals above the tree line. If my corpse wasn’t already destined for the dissection table, I might find the sky burial a fitting way to decompose, myself.

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