Thursday, January 24, 2013

The Leptoptilos Storks: Why You Have Every Right to Fear Them

We usually associate storks with the widespread and familiar white stork Ciconia ciconia. Most members of the family Ciconiidae, found on every continent with the exception of Antarctica, are similarly plumed, with some tropical species displaying more vibrant patterns of feathers, beaks, and skin. Most of these long-legged and –billed birds feed on small prey, ranging from fish to frogs to molluscs. However, one genus betrays the grace and beauty so often associated with these birds.

Greater adjutants L. dubius in a garbage dump in Guwahati. Photo by Yathin on Flickr.
Enter the Leptoptilos storks: bald-headed, ungainly, carrion-loving animals ranging from sub-Saharan Africa to southern Asia. Comprising of three extant species, the Leptoptilos storks lack any and all forms of purity, grace, and fragility associated with their baby-carrying relations. They are scavengers by nature, appearing and behaving like vultures on stilts. Adding to their already unpleasant description, they are seemingly fond of garbage dumps, and groups of the critically endangered Asian species are commonly seen alongside humans scrounging for scraps. Photos of such scenes, primeval-looking scavengers perched menacingly on mounds of human garbage, are chilling reminders that dinosaurs are alive and well in the modern world.

Marabou L. crumeniferus in Kenya. Photo by Lip Kee Yap on Wikimedia Commons.
The most common species is the African marabou stork L. crumeniferus. The English name “marabou” is a reference to the bird’s rather reserved demeanor, deriving from the Arabian “murabit,” meaning “quiet.” The Portuguese word “marabuto,” of similar roots, translates to “[a] hermit.” Ranging across the continent south of the Sahara, it is a common sight alongside various species of both avian and mammalian scavengers. Measuring up to 1.5m (~5ft) tall and equipped with a formidably heavy bill, they have a distinct advantage over other scavengers against which they compete at carcasses. Though they are brilliantly adapted for scavenging, they will also accept both live fish and scraps from humans, as well as small reptiles, mammals, and insects kicked up by herds of large mammals. The breeding habits of this species vary with local habitats and latitudes; breeding occurs in the dry season in populations closer to the equator. Colonies number anywhere 20 breeding pairs to thousands of them, and small groups usually stick together when feeding.

Lesser adjutant L. javanicus in flight. Unlike most storks, the Leptoptilos genera fly with their necks tucked close to the body. Photo by Lip Kee on Flickr.
The remaining two extant species are restricted to southern Asia. These are the adjutants, referring to their likeness to men in “stiff dress pacing slowly on a parade-ground.” The adjutants are comprised of two species: the greater L. dubius and lesser L. javanicus. These charismatic birds have been described in literature and travel accounts as early as 1773, when John Latham’s illustration of the “gigantic crane” was published. An adjutant even appears Rudyard Kipling’s The Second Jungle Book, appearing in a grim trio alongside a crocodile and a jackal. Both species breed in the dry season, when prey is concentrated into smaller pools of water. L. dubius, now classified as endangered, was once widespread, though the current population may number up to 1,800 birds, based on surveys of various breeding colonies. The largest modern breeding colony can be found in Assam, India, consisting of up to 800 individuals, though recently this colony has experienced various nesting failures. This may be due to disease, as well as the reduced use of garbage dumps as placed to dispose of food scraps and livestock carcasses. Competition for nesting space with lesser adjutants may pose another threat to this species, as well as their local reputation as nuisances. The smaller L. javanicus is far more common, with a worldwide population of up to 8,000 individuals spread from Sri Lanka to Indonesia. They are less dependent on garbage dumps and human-produced waste than the greater adjutant, spending more of their time in forested wetlands, with coastal populations inhabiting mangrove swamps and tidal flats.

L. robustus and Homo floresiensis. L. robustus measures approximately 1.8m (~6ft) tall; H. floresiensis approx. 1.06m (~3.5ft). Illustration by I. van Noortwijk, from Due & Meijer, 2010.
While the extant species of Leptoptilos may be intimidating, both in habits and in appearance, the various extinct species were truly monstrous. Most of these fossil species were similar in size to modern species, and filled the niche as large avian scavengers. However, some species grew to enormous proportions. L. robustus shared its habitat on the Indonesian island of Flores with a variety of endemic species, all products of the wonderful forces of insular evolution. On this island, giant monitor lizards and rats roamed alongside dwarf stegodonts and hominids. With no other scavengers, and only monitor lizards to serve as predators, Flores’ Leptoptilos stork evolved into a gargantuan bird, measuring a whopping 1.8m (~6ft) tall. An estimated weight of 16kg (~35lb) implies a largely reduced ability to fly. (Due & Meijer, 2010) With its size and heavy bill, L. robustus could have easily preyed on anything on which it could clamp its bill. L. falconeri, which lived in the Pliocene, was a widespread species, ranging from eastern Africa to Europe to southern Asia. It was similarly gigantic, and probably had a much more varied diet. L. falconeri coexisted with some of our ancestors in its African range. (Brunet et. al, 2005)

Marabou L. crumeniferus and a lappet-faced vulture Torgos tracheliotus. The marabou's height and long bill give it an advantage over shorter scavengers. Photo by Lip Kee on Flickr.
The Leptoptilos storks are unsightly, quiet animals, more than deserving of their nickname as “undertaker birds.” However, their grim appearance often overshadows how remarkably well-adapted and unique they are. They completely betray their family history as fishers and hunters of small invertebrates, and have instead evolved to compete alongside aggressive vultures and jackals, as well as eke out a living from the trash and waste produced by humans. The giant species which once roamed Eurasia and Africa are haunting reminders of the terror-birds which once stalked the plains of the Americas, and, in the eyes of their prey, were just as fearsome. As grotesque and bizarre as they may be, their natural history proves how variable just one family can be.

Brunet, M.; Likius, A.; Louchart, A.; Vignaud, P.; and White, T.D. 2005. A large extinct marabou stork in African Pliocene hominid sites, and a review of the fossil species of Leptoptilos. Acta Palaeontologica Polonica 50, 549-563.

Due, R.A. and Meijer, H.J.M. 2010. A new species of giant marabou stork (Aves: Ciconiiformes) from the Pleistocene of Liang Bua, Flores (Indonesia). Zoological Journal of the Linnean Society 160, 707–724.

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