Life Everlasting

by Bernd Heinrich

  I do not know how much of the raven-cached meat is recovered, either by the ravens who cached it or by other animals, but I suspect it could be a lot. Meat has scent, and Hugo seems to find the ravens’ caches quite easily, even those he did not observe being made.

  When ravens feed at a carcass in the winter, there will soon be meat scattered for kilometers around. Much of it will be taken by coyotes, weasels, deer mice, red-backed voles, flying and red squirrels, fishers, and both short-tailed shrews (Blarina) and common shrews (Sorex). Thus any carcass that ravens feed on in the winter will be recycled, not only into the birds but also into a large portion of the mammal fauna that needs meat to survive the frozen season.

  NOTE: AS THIS book was going to press in November 2011, a lone raven with a white feather in its right wing was sighted on the ground in a clearing near my cabin. This put a new wrinkle in my story about Whitefeather, especially because during that same period I had seen some very unusual raven behavior. I awoke on November 9 from solid sleep about 5:30 A.M., hearing agitation calls from “my” pair of ravens at their usual roost site in the pines next to my cabin. As I stepped outside into the early morning darkness, the pair lifted off and began to circle the clearing. A third bird continued to call from the pines, then joined the pair but soon returned to the trees. The pair in the air kept up a continuous conversation of nasal hanks and honks, squeals, kecks, hooting, and knocking calls (the female courting calls). The calls got fainter and fainter to my ears as the birds circled perhaps more than a mile above me. The third bird remained perched, occasionally calling loudly.

  The pair were still cavorting after it was fully light; I saw them as barely visible black specks dancing above the clouds. I stood spellbound, continuing to take notes on what I later wrote was “an incredible raven experience—I was almost breathless with wonder—I’ve never experienced anything like this.”

  They performed their sky dance, during which I never saw them more than three feet apart, for at least an hour before bursting through the clouds like black thunderbolts. They pulled in their wings and shot almost straight down, then caught the air again, gracefully spiraling up and again falling like rocks. It was a ballet of sound and motion.

  At noon and then at 4:20 P.M., when it was almost dark, I again observed their dance. At dark they returned to their sleeping place in the pines, but this time I heard the aggressive, staccato keck calls, accompanied by a vigorous, straight-out chase, the birds skimming directly above the treetops. A third bird followed, seemingly passively.

  The next morning at 5:30, with the stars still shining brightly, the ravens again woke me, and I jumped out of bed. They repeated their aerial display. The third bird stayed in the trees in the vicinity, occasionally making the long, undulating territorial calls that I have come to believe are unique to the ravens who own this hill. The pair stayed aloft for forty-five minutes before returning to earth. Again they interacted with a third bird, although I could not determine what was going on because they were flying through the forest. I was never close enough—or above them—to determine whether one was Whitefeather, though I suspected so.

  Without being able to identify the individuals or to follow them through the vastness of their domain, I can’t possibly say what was going on. Except for one thing: I may have made an error of interpretation due to an assumption.

  In January 1998 I had assumed that it was Whitefeather who returned with Goliath to their old nesting site, the aviary. I now think it equally likely that there had been a divorce, and the new bride reluctant to enter the aviary was in fact not Whitefeather, who might have returned to her old territory on release. Perhaps now, thirteen years later, she had, for any of several reasons, come back. Perhaps Goliath was now trying to reaffirm his old bond with her, thus pitting his new mate against the old one, as each contested for the same mate and the same territory. Given what we know, there are several possibilities; many tales could be spun.

  The Vulture Crowd

  MY FIRST MEMORABLE ENCOUNTER WITH VULTURES OCCURRED when I was twenty-one years old and in Tanganyika (now Tanzania), East Africa. I was exploring “the bush” at the edge of Dar es Salaam. Here’s an edited version of what I wrote in my journal:

  October 24, 1961. The Africans here keep large herds of the multi-colored humpback cows. At night they are held in corrals of bushes and thorns but during the day the herdsmen drive them at a slow pace through the countryside. These cows all look rather skinny, and I think they are butchered only when sleeping sickness or some other disease overtakes them and they drop in their tracks. This morning I came across a freshly skinned carcass from which most of the meat had been hacked off. It was on the bottom of a narrow ravine, and could not have been visible from afar. It had not yet been touched by animals as it was just getting light (early in morning) when I came upon it. I returned to the spot an hour or so later and sat and watched and listened for a half-hour. At first only a few vultures perched in the surrounding trees. Some of them came closer to the carcass, and the trees they left were promptly occupied by others, who literally dropped themselves into the branches so that they shook and rattled. Then one or two dropped down to the carcass. Then, as if by signal, vultures were suddenly swooping in from all sides, and now they were no longer bothering to settle in the trees but instead came straight down into the ravine, plummeting on motionless wings past where I sat on the edge. The wind rushing through the wing feathers produced a flopping, droning sound, like a flag in a hurricane. As more vultures swooped down, more came in. In the distance I saw black specks that were formations of still more vultures that could not possibly see what was going on down below me in the gorge. They arrived in surprisingly short time, broke ranks, circled once or twice, and rushed down to the ground with outstretched legs. In half an hour there must have been 150 at the carcass. There was a large mass of them on top of each other and fighting from the sides to get in. It was all rather quiet except for the thrashing. Occasionally there was a squeak or a screech as two faced each other with outstretched naked necks and wings outside the squirming mass. After a while, some flew off with laborious wing-beats and settled in nearby trees. I saw others spiraling on motionless wings high in the sky. Swarms of them, with ever more arriving as if from nowhere—first as barely visible specks in the sky—until they overpowered my senses.

  In some places such scenes are still current. The wildlife biologist Richard Estes, leading a safari in Namibia in January 2011, told me of seeing about a hundred vultures around a recently dead giraffe carcass. When he went back to it an hour later, the carcass was still intact, but by then there were nearly three hundred vultures, apparently waiting for lions or hyenas to provide access to the meat. At about that same time, a visitor to the city of Dakar, Senegal (on the Atlantic coast of West Africa), told me of seeing “swarms” of vultures flying all over the city and “hopping along roadsides.” Pied crows, which in Africa take the place of ravens as scavengers, were in equal abundance. Many horses and goats roamed apparently free in town, along with dogs and cats. It is not hard to imagine the scene wherever a goat, horse, or cow dies or is butchered in an area where vultures live; there would be no scrap of offal left after several hours.

  UNDERTAKING SURELY IS an ancient heritage. Although undertakers were, and still are, often not differentiated from executioners, they have always been the essential link for the continuity of life; without them, life would have come to a grinding halt. Over millions of years, through evolution, the body size of herbivores and predators and their handmaidens, the scavengers, increased. As the herbivores grew larger, so could those that took advantage of their fallen bodies. For every individual that walks, one dies, and each one becomes a resource of highly concentrated food. The larger the carcass, the more food there is for those who feed on it. In turn, a large amount of food in one place for a short time favors larger scavengers, because it tides them over from one meal to the next.

  Consider the apatosaurs of the Cretaceous, 145 t
o 65 million years ago, the largest land animals that ever lived. Such huge meat piles, weighing as much as thirty-eight tons each (the equivalent of eight or ten African elephants), left regularly on the landscape, would have been used. The larger the meat pile, the more it was worth defending, and strong defense would also have favored large size. The tyrannosaurs, with their bulk of up to nine tons, were not suited for running pursuit and agile maneuvering. Their long, sharp teeth were adapted for ripping flesh, though, so they may well have been in the first tier of undertakers. Along with feeding on the already dead when opportunity afforded, they would have dispatched the old, the weak, and the injured. Yet a tyrannosaur would not have picked clean an animal as large as an apatosaur; there would have been plenty of scraps left over for many more tiers of undertakers. And, since carcasses of very large animals were by definition not numerous (a plant community can support only a certain amount of biomass), the long distances between potential meals would have favored the evolution not only of huge undertakers but also of some large flying ones.

  The gigantism of the Cretaceous herbivores probably explains why the largest known flying creatures, the pterosaurs, lived at that time as well. The largest of all, Quetzalcoatlus and Hatzegopteryx, had wingspans of at least ten meters and maybe up to twelve meters (the largest vulture today, the Andean condor, has a wingspan of three meters). Their size, which would have greatly compromised their maneuverability and ability to hunt, would have been an advantage both in fighting for carcasses and in getting to and surviving on infrequent but large meals. We can infer that these pterosaurs played a major role as the cleanup crew that swooped in to feed on the giant carcasses after the meat-eating dinosaurs had penetrated the hides and perhaps taken most of the easily accessible meat of their large herbivore prey. The pterosaurs would have been super-vultures.

  These giant meat-eating scavengers, specialized to travel far and to live off, and hence to require, huge carcasses, went extinct at the end of the Cretaceous when an asteroid struck the earth, causing climate changes that wiped out their food base. The small and relatively inactive reptiles, such as snakes, turtles, and crocodilians, who could live without food for months to perhaps a year or more, survived. But for some reason that is shrouded in mystery, one surviving line of small dinosaurs evolved to become what we now call birds. Some of the largest of these are the present-day vultures, who evolved as specialized undertakers of very large carcasses under the selective pressures postulated above for their ancient predecessors and ecological counterparts.

  Among the survivors of the Cretaceous asteroid impact were the first mammals, which at that time were small and inconspicuous. Over the next millions of years, some of them—as before, especially the herbivores—evolved to gigantism and occupied the niche that the large dinosaurs had held. By the late Miocene (the Age of Mammals), some six to eight million years ago, there existed a large assemblage of huge mammals, some of whom resembled our modern fauna. The mammoths, mastodons, giant beavers, glyptodons, giant ground sloths, and other giants existed almost to the end of the last ice age. Humans were for a while contemporary with this fauna. In a sense, the reptilian actors on the stage had been largely replaced by mammalian counterparts, and large birds had replaced the giant flying pterosaurs. At that time lived the largest flying bird ever discovered, Argentavis magnificens, commonly known as the giant teratorn. It had a wingspan of 6–8 meters (19–26 feet) and is estimated to have weighed 60–120 kilograms (140–240 pounds). The Andean condor is a midget in comparison. It is safe to guess that a large flying bird such as the giant teratorn had the habits of a condor or vulture, especially since its large, slender beak with a hook at the end was ideally shaped to tear flesh from the carcasses provided or opened by the dire wolves and great saber-toothed cats.

  Some of the teratorns persisted into the Pleistocene, and they, along with ravens, would have been well known by early man. One recent species, Teratornis merriami, was found in 10,000-year-old deposits in the La Brea Tar Pits in Los Angeles, along with dire wolves, saber-toothed cats, mastodons, and giant sloths—all now extinct. This teratorn had a wingspan of 4 meters (11.5–12.5 feet) and weighed around 15 kilograms (33 pounds); a California condor weighs about 20 pounds. It would have been a contemporary of the Paleo-Indians, such as the Clovis hunters, who preyed on the North American megafauna. With their extinction, that teratorn also disappeared, as did another of the largest avian undertakers, Aiolornis (originally Teratornis) incredibilis, which was first described from only a single individual, discovered in Smith Creek Cave, Nevada. The bird probably had a wingspan of 16 to 20 feet. Present-day vultures regularly fly a hundred miles to feed. This teratorn surely had an even greater flight range.

  There are other, generally large, carcass-scavenging birds. The vulture habit evolved in the South American caracara (a falcon) and in the African marabou stork, Leptoptilos crumeniferus, which has converged on vultures in having a naked head and neck, which greatly helps solve or eliminates the problem of feather hygiene. To some extent the vulture habit exists also in eagles; the bald eagle feeds on dead fish and other offal, as does the bearded vulture, Gypaetus barbatus, a Eurasian eagle that lives almost exclusively on carrion.

  Vultures evolved at least twice and arguably several times. The present-day “true” vultures are divided into seven New World and fifteen Old World species. The vultures of Asia, Europe, and Africa belong to the family Accipitridae and are thought to be relatives of hawks and eagles. Some, like the griffon vulture, Gyps fulvus, have naked heads. Although the bearded vulture has a fully feathered head and eats mostly carrion, it prefers fresh meat and specializes on bone marrow; it shatters large bones by dropping them from great heights onto rocks. Many of the vultures of North and South America, family Cathartidae, are similar in appearance to those Accipitridae that specialize in rotting meat and have naked heads. Resemblances between the two groups result from convergent evolution, with similar adaptations favoring the same feeding habit. The Cathartidae may be derived from storklike birds; their origin is still debated.

  Vultures, regardless of taxonomic affiliation, are specialized carrion scavengers of large animals. Many prefer fresh meat, and some, like the black vulture of the Americas, will, like ravens, hunt live prey. Few other scavengers (such as wild pigs, dogs, and eagles) can compete with them for decomposed meat because they are able to metabolize (detoxify) natural bacterial biotoxins. Their habit of feeding on rotting carrion in warmer regions seems to work to these vultures’ advantage, perhaps in part because it makes them taste bad; few animals eat them. Indeed, they use their partially digested food in projectile vomit as a defense, and if that tactic alone doesn’t work, some “play possum,” which is presumably most effective if their feathers are soiled and they smell appropriately necrotic after a rotten meal.

  Vultures tend to be social, often roosting, and sometimes nesting, in colonies. This predisposition allows them to bond with people, and they are said to make good pets. A friend of mine, who was bonded to an Andean condor (and vice versa), traveled with it in his van and let it fly free on occasion, to show off the bird’s awesome size and beauty. The van was its cave, to which it returned and where it roosted contentedly as long as it was well fed on fresh meat.

  Vultures live primarily in warmer climates. When several species coexist, as they do in Africa, “guilds” consisting of several species use carcasses cooperatively, with each species specializing; mutual dependence then commonly results. In the Americas, for example, a turkey vulture is usually one of the first vultures to arrive at a hidden carcass, which it can detect by scent. Other vultures, lacking a strong sense of smell, find the carcass by following the turkey vulture. The turkey vulture, however, being relatively small, cannot tear into a large carcass. The larger vultures, such as the Andean condor, make the meat available to them, but at the cost to the turkey vulture that the larger birds feed first.

  Vultures, not having to chase and capture prey, tend to be slow and to ha
ve low metabolism. They find food by soaring, which has nearly the same metabolic cost as perching—it’s the equivalent of perching in the sky. But soaring requires warm updrafts. At night the vultures’ body temperature drops, saving more energy. Because of their large size and because they have a crop in which to store food, allowing them to gorge when and where a quantity of food is available, they are also adapted to survive fasts of several weeks or more.

  The vultures’ conservative lifestyle is reflected in their natural history. They take a long time to reach sexual maturity—six years in the larger species. They live long; Andean condors have a lifespan of at least fifty years, and a griffon vulture has lived forty years in captivity. Having adapted to a low natural mortality rate, they have a correspondingly low reproductive rate. The larger species breed only once every two years and have only one chick per clutch, while the smaller species may have two.

  NOWHERE IN A NATURAL ecosystem is the task of carcass creation and disposal more out in the open to human eyes than in the Serengeti region of East Africa, an intact ecosystem with a virtually Ice Age fauna. Six species of vultures live there. Some 12 million kilograms (the weight of about 200,000 men) of soft tissue (meat) per year is available for vultures in the Serengeti, and the birds find almost all carcasses, even those hidden in thick brush.

  The specific scenarios of undertakers of large carcasses in Africa vary, but the pattern is like the following partial sequence I observed in 1995 at the carcass of an adult reticulated giraffe, Giraffa camelopardalis, the largest ruminant and also the tallest land animal. Bulls may be 19 feet tall and weigh more than 4,000 pounds. There is a lot of meat on the platter for scavengers when one of these animals drops.