HIBERNATION
Some mammals that live in places with a cold winter hibernate. Hibernation is a process in which animals in temperate climates go into a deep sleep and refrain from eating or drinking to survive the cold and lack of food in the winter. A way to conserve energy when food is scarce, hibernation is characterized by a significant slowing of metabolic rate, reduced body temperature, and decreased heart rate. While hibernation is similar to sleep, it involves more drastic physiological changes and can be fatal if an animal is awakened from hibernation.
The body temperature of hibernating animals can drops by as much as 37̊F to 50̊F. The body uses just 13 percent of the energy it does when its awake. During hibernation, the central nervous system (CNS) experiences a significant reduction in activity, but its functions are generally maintained, especially in specific regions. While neuronal activity decreases, some regions retain the ability to generate action potentials in response to stimuli, including those in the peripheral system and primary central areas. The hypothalamus and brainstem, which are involved in thermoregulation and autonomic functions, also undergo changes during hibernation.
Key Characteristics of Hibernation:
1) Reduced Metabolic Rate: Hibernating animals significantly slow down their metabolism, burning fewer calories and using less energy.
2) Lowered Body Temperature: Body temperature drops significantly, sometimes to near freezing.
3) Reduced Heart Rate: Heart rate slows down considerably, often by up to 90%.
4) Reduced Breathing: Breathing rate also decreases, allowing animals to survive without eating or drinking for extended periods.
5) Triggers: Hibernation is triggered by various factors, including low temperatures, food scarcity, and changes in daylight hours.
6) Aestivation (Summer Sleep): While some animals hibernate during the winter, others enter a state of to survive during periods of heat and drought. [Source: Google AI]
Deaths during hibernation are rare even though the rate of blood flowing to the brain is 10 percent of normal. If the human brain were deprived of that much blood death or major brain disorders would result. Scientists are studying hibernation and its applications to humans, particularly for space travel, preservation of organs for transplants and regulation of the blood during surgery
See Separate Article: BRUMATION, DIAPAUSE, FREEZING: HIBERNATION-LIKE PROCESSES OF ANIMALS factsanddetails.com
Hibernating and Near- Hibernating Animals
Marmots hibernate to to conserve energy and avoid the harsh winter conditions where many of them live. Black-capped marmots of Siberia hibernate for eight ot nine months from September to mid-May depending on the environmental conditions and how long food sources are available aboveground. They hibernate in groups and have the ability to lower their body temperatures to around 0°C during hibernation, Arousals occur every two to four weeks, in which case the marmots are believed to defecate and urinate. In addition to saving energy by group hibernating, black-capped marmots and hibernate when ambient temperatures are below 0°C. Even during arousal periods, body temperatures do not rise to their usual active body temperature. These marmots roll into balls and press together while in hibernation. [Source: Animal Diversity Web (ADW)]
Bears hibernate for several months during the winter, they curl up in dens and their body temperature drops to about 95 degrees Fahrenheit. Some scientists argue bears don’t hibernate because their temperature doesn’t drop low enough. Traditionally the term hibernation was reserved for "deep" hibernators such as rodents, but is has been redefined in recent years to include animals such as bears and is now applied based on active metabolic suppression rather than any absolute decline in body temperature. See Below
Bats employ hibernation because it allows them to survive the winter months when food is scarce. During hibernation. bats’ body temperature lowers and their metabolic rate slows, and they they survive on the fat they have stored up instead of trying to forage for food. During hibernation, bats need roosts that are cool and remain at a constant temperature. They often move into underground sites, such as caves. [Source: Bat Conservation Trust]
Hedgehogs enter a state of torpor during the winter, with their body temperature dropping significantly. Torpor: is a temporary state of slowed metabolism and reduced activity, often seen in daily or weekly cycles. Hibernation is longer-term, and a more extreme form of torpor, lasting for months during the winter. Many scientists now believe that the processes of daily torpor and hibernation form a continuum and use similar mechanisms
Squirrels found in temperate climates don't hibernate in the same way as bears or bats, but they do enter a state of torpor during the winter. Cold-weather squirrels expereince some of the extreme temperature drops during hibernation. Hibernating Arctic ground squirrels may exhibit abdominal temperatures as low as −2.9°C (26.8 °F), maintaining sub-zero abdominal temperatures for more than three weeks at a time, although the temperatures at the head and neck remain at 0 °C (32 °F) or above.
Different Forms of Hibernation
Hibernation may last days, weeks, or months—depending on the species, ambient temperature, time of year, food abundancy and the body-condition and health. Some species of mammals hibernate while gestating young, which are born either while the mother hibernates or shortly afterwards. Female black bears, for example, go into hibernation during the winter months and give birth to their offspring during it. Pregnant mothers significantly increase their body mass prior to hibernation, and this increase is reflected in the weight of the offspring. Fat accumulation enables them to provide a sufficiently warm and nurturing environment for their newborns. During hibernation, they subsequently lose 15–27 percent of their pre-hibernation weight by using their stored fats for energy. [Source: Wikipedia]
Olivia Judson wrote in Natural History magazine: Hibernation takes different forms in different animals. A black bear, for example, drops its body temperature by only a few degrees, and spends the winter in a kind of deep and continuous sleep. During that time, it neither urinates nor defecates. For small mammals such as bats and ground squirrels, in contrast, hibernation typically features profound drops in body temperature, during which the animal is inactive, punctuated by regular bouts of warming up to normal and rousing into activity for some hours. The Arctic ground squirrel in particular may be the most extreme case. During regular life, its core body temperature, like ours, hovers around 98.6 degrees Fahrenheit. But during hibernation, its core body temperature can actually fall below freezing, to as little as 26.8 degrees, for days at a time. How do Arctic ground squirrels manage that? They supercool. [Source: Olivia Judson, Natural History magazine, December 2007/January 2008]
Supercooling is what happens when the temperature of a liquid falls below its freezing point yet doesn't freeze. That can happen if a liquid has no nucleating agents — no particles around which crystals can form. But add a particle — a piece of ice, say — to a cup of supercooled water, and pow! The entire cup of water will freeze instantly. Being able to supercool is rare among mammals — but popular among insects. In Alaska, yellowjacket queens of the species Vespula vulgaris survive the cold, hanging by their mandibles for nine months in a dry, snow-free cavity, by allowing the fluids in their bodies to supercool. A supercooled yellowjacket can drop her temperature to as low as 3 degrees, but rather miraculously avoids turning into a waspsicle. Bring her into contact with snow, however, and again, pow! She freezes solid — which kills her. Other insects can get even cooler: the beetle Rhagium inquisitor, otherwise known as the ribbed pine borer, can supercool to —24 degrees. Is a supercooled Arctic ground squirrel at risk of freezing solid? It's possible, but unlikely. Its skin would have to be pierced by an icicle or something like that.
Hibernation Processes
Before entering hibernation, animals need to store enough energy to last through the duration of their dormant period, possibly as long as an entire winter. Larger species become hyperphagic, eating a large amount of food and storing the energy in their bodies in the form of fat deposits. In many small species, food caching replaces eating and becoming fat. [Source: Wikipedia]
Olivia Judson wrote in Natural History magazine: How does an animal begin to hibernate? It goes to sleep. Indeed. one of the first things that happens in slow-wave sleep (as opposed to rapid-eye-movement sleep) is that body temperature drops a little. But whereas your body temperature won't drop more than a degree or so, the body temperature of a hibernating animal keeps going down as its metabolic processes slow down. Some animals let their temperatures drop low on a daily basis, essentially hibernating for a few hours in the night (or day) — a condition known as torpor. But, interestingly, many animals, such as hummingbirds, that become torpid do not hibernate for longer periods. And if an animal begins to hibernate by going to sleep, what does it do upon rousing from hibernation? Oddly, the first thing a ground squirrel does is . . . take a nap. Why? No one knows.
Hibernation, on many levels, looks passive, almost like a temporary death. In a small mammal, the body is cold, the heart rarely beats, the animal scarcely breathes. A hibernating little brown bat, for example, may take a breath less often than once an hour. The cellular machinery shuts down, too: little DNA is copied, few proteins are made. But hibernation is far from being a full suspended animation. For one thing, many hibernating animals remain alert to unusual noises or disturbances. (Cough loudly in a cave full of hibernating bats, and they w ill start to rouse. Stride into a bear's den, and the bear will wake up — and it probably won't be pleased to see you. Moreover, hibernation is tightly regulated, Ground squirrels punch in and out of hibernation with clockwork precision — somehow, they measure time — and their body temperatures are always kept a bit higher than the temperature of their dens.
Obligate Versus Facultative Hibernation
Obligate hibernation refers to animals that spontaneously, and annually, enter hibernation regardless of ambient temperature and access to food. Obligate hibernators include many species of ground squirrels, other rodents, European hedgehogs and other insectivores, monotremes, and marsupials. These species undergo what has been traditionally called "hibernation": a physiological state wherein the body temperature drops to near ambient temperature, and heart and respiration rates slow drastically. [Source: Wikipedia]
The typical winter season for obligate hibernators is characterized by periods of torpor interrupted by periodic, euthermic arousals, during which body temperatures and heart rates are restored to more typical levels. The cause and purpose of these arousals are still not clear; the question of why hibernators may return periodically to normal body temperatures has plagued researchers for decades, and while there is still no clear-cut explanation, there are multiple hypotheses on the topic. One favored hypothesis is that hibernators build a "sleep debt" during hibernation, and so must occasionally warm up to sleep. This has been supported by evidence in the Arctic ground squirrel. Other theories postulate that brief periods of high body temperature during hibernation allow the animal to restore its available energy sources or to initiate an immune response.
Facultative hibernators enter hibernation only when either cold-stressed, food-deprived, or both, unlike obligate hibernators, who enter hibernation based on seasonal timing cues rather than as a response to stressors from the environment. A chipmunk, for example, is a facultative hibernator. Even though it sleeps for a long period of time, it is not a true obligate hibernator. This is because during the long period of sleep, its temperatures do not decrease to the low levels of hibernation. It only truly hibernates if food is scarce. A good example of the differences between these two types of hibernation can be seen in prairie dogs. The white-tailed prairie dog is an obligate hibernator, while the closely related black-tailed prairie dog is a facultative hibernator.
Bear Hibernation
Bears don't hibernate in the true sense of the word in that their temperature remains relatively normal and they can easily be roused from their sleep. The temperature of true hibernating animals — namely small mammals such as chipmunks or marmots — drops much lower, sometimes to near zero, and they can not be easily roused. Bears go into a dormant state and have a significate drop in pulse rate (8 beats a minute as opposed to 40 0r 50 beats a minute when sleeping in the summer) and breathing rate but their body temperature (in the case of black bears) only drops from a normal of 100̊F or 101̊F to 88̊.
Hibernating bears hibernate from two to six months, even in warm climates where there is plentiful food supply. Some individuals of hibernating species don’t hibernate even when there is a lot of snow and food is in short supply. Hibernation seems to be triggered by low temperatures, shorter days and snow and coincides with the disappearance of high-quality food. During late summer some bears eat over 20,000 calories a day to put on enough fat to last them through the winter. During the days before hibernation some species eat highly fibrous materials that act as anus plugs during hibernation. If given sufficient food zoo bears don’t hibernate.
Bears consume no food or water and don’t urinate or defecate while hibernating (smaller mammals by contrast have to periodically wake up and eat and expel waster). The water content of the blood remains at a constant level . The small amount of water loss that occurs naturally is offset by the breakdown of fat reserves to secure moisture. Bears burn about 4,000 calories a day while hibernating. The sometimes shiver while hibernating to stay warm. After they wake up it takes several weeks for them to resume normal eating, presumably because it takes some time for the metabolism to resume to normal.
Bears emerge from their dens after the hibernation is over with no significant loss of muscle strength. Humans immobile for the same amount of time lose 90 percent of their muscle strength. Nitrogenous waste of hibernating bears is recycled through the bladder and reabsorbed and not excreted as urine. Their body reprocesses the urine and converts it to an amino acid that is necessary to keep the bear alive. Scientist are studying how bears do this as a way of helping people whose kidneys have failed.
Bones of hibernating bear don't lose calcium and become brittle. Scientist are studying this phenomena as way of treating older people with osteoporosis. Sleeping bears don't suffer from obesity even though they sometimes carry huge amounts of fat. They tolerate high levels of cholesterol without developing arteriosclerosis; burn about 4,000 calories a day, but limit the fuel to body fat while preserving protein reserves. Scientists are studying these processes to help burn victims (who often die of rapid protein depletion).
See Separate Article: BEAR HIBERNATION, REPRODUCTION, CUBS factsanddetails.com
Fat-Tailed Dwarf Lemurs — Tropical Hibernating Primates
No primate or tropical mammal was known to hibernate until the discovery of hibernation in the fat-tailed dwarf lemur of Madagascar, which hibernates for seven months of the year in tree holes . Winter temperatures sometimes rise to over 30°C (86 °F) in Madagascar, so hibernation is not exclusively an adaptation to low temperatures.
The hibernation of the fat-tailed dwarf lemur is strongly dependent on the thermal behaviour of its tree hole: If the hole is poorly insulated, the lemur's body temperature fluctuates widely, passively following the ambient temperature; if well insulated, the body temperature stays fairly constant and the animal undergoes regular spells of arousal.
Olivia Judson wrote in Natural History magazine: The fat-tailed dwarf lemur hibernates to escape not cold, but drought. The animal beds down in a treehole, often snuggled with its mate and perhaps a couple ol their offspring, for as long as seven months, even though the outside air can reach a balmy 85 degrees. [Source: Olivia Judson, Natural History magazine, December 2007/January 2008]
A fat-tailed dwarf lemur doesn't bother to rouse if it's hibernating in a poorly insulated tree-hole, one that lets air temperature exceed 85 degrees. Instead the lemur abandons control of its body temperature altogether, letting it (and presumably also its metabolism) fluctuate with the temperature of the air. But a lemur that's settled into a tree trunk that has thick walls and a cool interior — a castle among tree trunks — keeps its body temperature steady at 77 degrees, and rouses for a few hours about once a week. (Maybe the reason bears don't do such systems checks is that they never let their bodies get much colder than about 90 degrees.)
Evolution of Hibernation
Olivia Judson wrote in Natural History magazine: Hibernation seems to have evolved as a way to save energy when food is scarce, rather than a way to bypass winter months. That is why it isn't found only in cold climates as the fat-tailed dwarf lemur described above attests.[Source: Olivia Judson, Natural History magazine, December 2007/January 2008]
But cold climates do encourage energy-saving methods. Mammals maintain their high body temperatures by burning fuel, and it costs more to stay warm when the difference between the usual body temperature and the outside air is large. It costs more for a small mammal to adjust to dropping temperatures than for a big one (smaller animals lose heat faster). In short, it is hard for an animal the size of a mouse to stay warm when the weather is below freezing for weeks on end; thus, lowering the body's thermostat saves on heating bills. So it's all the more mysterious that ground squirrels bother to warm up every ten days or so. Warming up is expensive. Indeed, that's the main energetic drain ot hibernating.
Hibernation likely evolved simultaneously with endothermy ( warm-bloodedness, is the ability of an organism to generate and maintain its body temperature internally), with the earliest suggested instance of hibernation being in Thrinaxodon, an ancestor of mammals that lived roughly 252 million years ago. The evolution of endothermy allowed animals to have greater levels of activity and better incubation of embryos, among other benefits for animals in the Permian and Triassic periods. In order to conserve energy, the ancestors of birds and mammals would likely have experienced an early form of torpor or hibernation when they were not using their thermoregulatory abilities during the transition from ectothermy to endothermy. [Source: Wikipedia]
Hibernation and the Brain
Olivia Judson wrote in Natural History magazine: The hibernating brain gets almost no oxygen, yet the animal doesn't suiter brain damage. Understanding how that works could lead to better treatments for stroke and head trauma. [Source: Olivia Judson, Natural History magazine, December 2007/January 2008]
Indeed, ground squirrels have much to teach about brain regeneration. Studies ot the golden-mantled ground squirrel show that during hibernation they retract many of their dendrites — the tendril-like nerve-cell endings that receive information from other neurons. Such a disappearance of dendrites is usually associated with senility. Yet each time the animal rouses, though it's only for a few hours, it regrows its dendrites. What's more, the dendrites grow faster when the animal emerges from hibernation than they do during embryonic development — a period usually thought to be the pinnacle of speedy neural growth. In the brain of an embryonic rhesus monkey, for example, dendrites can grow 1 14 microns per day (about the thickness of a human hair). The freshly roused adult ground squirrel can accomplish the same growth in just two hours. Strange.
Why would an animal repeatedly dismantle and then rebuild the connections in its brain? Again, the answer isn't clear. One possibility, favored by the hibernation expert H. Craig Heller, a professor of biological sciences at Stanford University, is that during hibernation, it is too difficult to properly maintain the dendrites, so it's better to get rid of them and start over than to have to repair them. In support of that idea, he and his colleagues have shown that retraction is more extensive in animals that get colder. That makes sense: the lower the body temperature, the more complete the general shutdown, and the harder it would be to keep the dendrites in good order. Irrespective of why it happens, though, understanding how ground squirrels regenerate their brains might help develop therapies for the regeneration of damaged human ones.
Humans and the Medical Application of Hibernation
Olivia Judson wrote in Natural History magazine: Human hibernation is a hot topic, as I discovered one afternoon when I happened across the Journal of British Interplanetary Science. Space agencies are interested because the ability to hibernate on demand would come in handy on long-haul space flights. The immortality crowd is interested too: if you've got an incurable disease or simply won't settle for an 80-year-life span, wouldn't it be great if you could put your head down, catch forty million winks, and wake up when medical science catches up? [Source: Olivia Judson, Natural History magazine, December 2007/January 2008]
But the applications aren't all so futuristic; some are much closer to home. For instance, Matthew T. Andrews, a biologist at the University of Minnesota in Duluth, foresees that discoveries from hibernation biology will be useful in treating everything from heart conditions and hypothermia to obesity. Indeed, writing earlier this year in the journal BioEssays, he argued that "there is tremendous potential for applying hibernation strategies to improve the human condition."... It turns out that when they hibernate, animals overcome what currently look to us like intractable medical problems. For instance, cold-temperature hibernators, such as bats and ground squirrels, put themselves through rigors that would kill us. Most mammals that don't hibernate — such as mice, rats, and humans — die of heart failure if you cool the heart below about 70 degrees.
Several other aspects of hibernation turn out to be of potential medical interest. Take black bears. They don't move for months — they often start hibernating in October and don't emerge until April — yet their muscles don't waste away. A man confined to bed for six months would not be so lucky: his muscles would atrophy to about 20 percent of their prior strength, and on getting up, he'd find it difficult to walk. It isn't clear how T the bears manage to keep their muscle tone, though preliminary studies suggest that hibernating bears engage in regular episodes (that is, three or four times a day) of vigorous muscle contractions, a k a shivering. [Source: Olivia Judson, Natural History magazine, December 2007/January 2008]
At the same time, bears and other hibernators lose weight — Bears and their kind, because they keep their body temperatures relatively high; the deep hibernators. because ot the repeated bouts of warming. Moreover, hibernation burns up tat fast. For those with six months to spare, I foresee the hibernation diet, with the slogan: "Lose weight by doing nothing!" More seriously, hibernation could shed light on obesity and how to treat it. An animal preparing for hibernation suddenly starts gaining weight. The fat-tailed dwarf lemur doubles its mass in a few weeks, storing most of the fat in (you guessed it) the tail. Thus, understanding the underlying mechanisms of weight gain coupled with the subsequent weight loss could eventually lead to new anti-obesity drugs.
Hibernating Mice and Its Applications to Humans
Mice don’t usually hibernate but scientists have succeeded in making them do without harming them according to research led by Dr. Mark Roth of the Fred Hutchinson Cancer Research Center in Seattle and published in the April 22, 2005 issue of the journal Science. Nicholas Bakalar wrote in the New York Times: If the technique can be applied to humans, the scientists say, it may eventually offer new ways to treat hypothermia, slow down bleeding in traumatic injuries, quickly reduce high fevers, or even help heart attack patients in emergencies by slowing their breathing and heart rates. [Source: Nicholas Bakalar, New York Times, April 26, 2005]
In the study, they made use of a common gas, hydrogen sulfide. Within five minutes of breathing air that was 80 parts per million hydrogen sulfide, the mice dropped into a peaceful slumber, their oxygen consumption cut in half, their body temperature reduced to 58 degrees from a normal 98, and their breathing rate reduced to 10 breaths a minute compared with a usual 120. The researchers left them like this, fast asleep and apparently in no distress, for six hours. Then they turned off the gas and let them breathe normal air again. In short order, they were up and about, their body temperature and breathing restored to normal, and, to all appearances, acting like healthy mice. "They come out of it in about two hours," Dr. Roth said.
The process, according to the researchers, is similar to what happens in rare cases when someone falls into icy water: the body's metabolic rate -- the consumption of oxygen by cells -- declines so radically that the person can survive, completely unconscious and virtually deprived of oxygen, for several hours and then be revived without injury. In such cases, brain cells prevent damage by shutting down all activity until they receive the oxygen needed to go on working. Eric Blackstone, a graduate student at the University of Washington and a co-author of the paper, said that until now, "no one has been able to induce hibernation on demand, even in animals that can hibernate in the wild."
The mechanism of natural hibernation is not well understood, but the hydrogen sulfide gas technique precisely mimics its effects. Hydrogen sulfide works by inhibiting a specific enzyme in the electron transport chain, the part of a cell's energy-producing process that requires oxygen. With the mice, breathing rate and body temperature decreased in direct proportion to the amount of gas they were breathing.
Dr. Roth said that no one yet knows if the procedure would work in humans, or even in higher mammals, and that finding out would require considerable research and testing. But he expects that within five years, humans could begin to benefit from the work. Dr. Roth is a co-founder of Ikaria Inc., a biotechnology company that plans to develop treatments based on the process.For example, he said: "With a heart attack, you could be 'hibernated' while you're on the way to the hospital. We would hope that this procedure would buy time for you until you could get treatment." No one, however, should get the idea that depriving a person of oxygen is a beneficial treatment in an emergency, Dr. Roth emphasized. The procedure, he said, causes a reduction in use of oxygen at the cellular level, and "it's not the same as reducing oxygen by putting a plastic bag over your head." Hydrogen sulfide is produced in the human body, and Dr. Roth speculates that humans may have an evolutionary ability to use it to control oxygen use.
Hydrogen sulfide gas produces a characteristic rotten egg smell and is poisonous in large amounts. Olivia Judson wrote in Natural History magazine: Florian Midler, argues that reducing body temperature by just a few degrees would reduce metabolism and thus increase life span. Writing m the journal Rejuvenation Research, Mullerproposes living in a temperature-controlled box and breathing air mixed with minute quantities of hydrogen sulfide (to bring his temperature down just a smidgen) until medicine has progressed to the point where aging is abolished altogether. Of course, he writes, "one would have to be willing to tolerate . . . the slowing of other biological functions (e.g., probably reasoning, movement)." Is it worth it? Muller thinks "probably yes." Source: Olivia Judson, Natural History magazine, December 2007/January 2008]
Impact of Siberian 'Heatwaves' on Hibernation
Early winter in Siberia in 2006 was warmest in 70 years. Adrian Blomfield wrote in The Telegraph: Russian scientists gave warning that southern Siberia, already known as one of the fastest warming regions on the planet, is facing grave consequences as a result of the unnaturally temperate start to its typically harsh winter. November is normally a month when silence swathes the vast evergreen forests as migratory birds depart for warmer climes and resident mammals settle down to hibernate. [Source: Adrian Blomfield, The Telegraph, November 17, 2006]
This year, though, the forests are alive with uneasy sound. Bears and badgers have yet to hibernate, while hares, whose coats have changed from grey to white in anticipation of snow, have become easy prey.Even the plants seem confused. For the first time that worried locals can remember, dandelions and raspberries have bloomed in several parts of the region.
Some areas are recording highs of 12C, with temperatures across southern Siberia 7-10 degrees warmer than normal. A 380,000-square mile expanse of permafrost has started to melt, releasing into the atmosphere large quantities of methane and carbon dioxide, the main greenhouses gases that cause global warming.
If snow does not fall for another month, there is a risk that some bears and badgers could starve to death. "The longer these animals stay awake, the less fat they accumulated over the summer to prepare for hibernation will be left," said Anatoly Lobanchuk, the head of the veterinary department in the southern Siberian region of Kemerovo. Other conservationists reported that the situation was of even greater concern in northern Siberia. Ice packs are failing to form, forcing polar bears, seals and walruses to remain on land, disrupting breeding cycles.
Image Sources: Wikimedia Commons
Text Sources: Animal Diversity Web animaldiversity.org ; National Geographic, Live Science, Natural History magazine, CNTO (China National Tourism Administration) David Attenborough books, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Discover magazine, The New Yorker, Time, BBC, CNN, Reuters, Associated Press, AFP, Lonely Planet Guides, Wikipedia, The Guardian, Top Secret Animal Attack Files website and various books and other publications.
Last updated May 2025