Culture

The Killer Lions of Tsavo

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Pride of Tsavo lions
Lions in Tsavo National Park, Kenya

Humans are not at the top of the food chain. Throughout history, big cats have sometimes made a meal of us [5]. Although lions typically prefer large prey like buffalo and wildebeest, a 5000-year-old Egyptian cosmetic palette depicting lions eating the fallen on the battlefield tells us that lions have been known to prey upon people for a long time [5]. But one episode of human-lion conflict at the end of the nineteenth century really captured the popular imagination. The “man-eating” lions of Tsavo (SAH-vo) terrorized the Tsavo region of Kenya for nine months in 1898 [1-7] and may have preyed on humans unnoticed for several years prior [5]. The man who killed them, J. H. Patterson, was hailed as a hero [4, 5]. He estimated that the lions killed as many as 135 people [1-3, 5-7].

The Lions, the Colonel, and the Railroad

The lion’s roar was such that the very earth would tremble at the sound, and where was the man who did not feel afraid?

From epic poem gifted to Col. Patterson by his work crew [4]

The British Colonial Office was building a railway from the port of Mombasa, Kenya, to Nairobi, which was then in Uganda [3-5, 7]. Then they reached the Tsavo River. Tsavo means “place of slaughter” [3, 4]. Building a rail bridge over the river proved much harder than anticipated, at first mostly for engineering reasons such as locating the right type of stone locally [4]. So they hired a civil engineer to lead the Tsavo bridge project: Colonel J. H. Patterson [2-6]. Construction began in March 1898 [2, 4]. Very soon, he encountered a problem his education did not prepare him for.

“Our work was soon interrupted in a rude and startling manner. Two most voracious and insatiable man-eating lions appeared upon the scene, and for over nine months waged an intermittent warfare against the railway and all those connected with it in the vicinity of Tsavo,” Col. Patterson explained in his 1907 book The Man-Eaters of Tsavo and other East African Adventures [4]. They were large male lions without manes, working together, which is atypical behavior for lions. They attacked at night, tearing through the protective walls of thorns, called bomas, that the rail workers built around their camps, and then dragging sleeping people from their tents off into the bush [4].

Col. Patterson considered it his responsibility to do something to protect his work crew, so he turned everything he’d learned from his big game hunting hobby toward killing the Tsavo lions [4]. But the lions managed to evade him for months. They never struck the same encampment twice in a row, making it impossible for him to stake them out [4]. At first the lions were easily kept at bay by fire and loud noises, but they became less and less afraid of human things as time wore on [4]. The only thing that seemed to deter them was being out of their reach, so the crew went on strike December 1st to be allowed to build elevated sleeping platforms [4]. It was this work stoppage that finally brought the slaughter to international attention [5].

J. H. Patterson and Tsavo lion
Col. Patterson with first Tsavo lion – Photo from Field Museum on Wikimedia Commons

Later that month, however, Col. Patterson finally caught a break. He baited the lions with the corpse of a donkey that one of them had already killed when attacking a camp [4]. He hoped that one or both lions would come back to finish eating their kill, so he had a rickety platform built to keep watch on [4]. The lion did return, but decided to stalk Col. Patterson instead [4]! Col. Patterson managed to shoot the lion dead before being killed himself [4]. A couple weeks later, he baited the second lion with a trio of goats and killed it as well [4, 5]. Both lions were over 9 feet (2.7 m) long [4, 6].

Col. Patterson detailed the deaths of 14 victims in his book but put the total at “no less than twenty-eight Indian coolies, in addition to scores of unfortunate African natives of whom no official record was kept” [4]. The railroad office in London recorded the deaths of 28 railroad workers who fell prey to the Tsavo lions [3, 5]. Col. Patterson later specified that 107 locals were killed, which is how we get the 135 number [5]. However, research conducted at the Field Museum many years later estimated that the lions actually consumed about 35 people during their lifetimes [1, 2]. Human flesh made up about 30% of one lion’s diet and 13% of the other’s [1].

Why did the lions of Tsavo become man-eaters?

Patterson didn’t give much attention to this question, giving only such dismissive explanations as the lions’ incredible savageness and “sheer insolent contempt for man” [4, 6]. In his time and place, animal behavior and cognition were not front of mind. The lions killed humans because they were evil, and that was that [4]. But we have learned a lot about why animals do what they do in the past 125 years. Researchers have come up with several theories of what motivated the lions of Tsavo to kill and eat humans.

Bad Teeth

In the late 1990s, researchers examined the skulls of the Tsavo man-eaters and discovered significant dental problems [1, 2, 5]. The first lion Col. Patterson killed had a severely broken canine that exposed the tooth pulp, a root tip abscess, and three missing incisors [1-3, 5]. The scientists believed the injuries happened early in life because the lion’s jaws had changed shape from the asymmetry of its teeth [1, 5]. They hypothesized that the injuries were caused by a kick or strike from the horn of the lion’s prey and may have made it difficult for him to catch the tough-skinned wild animals lions typically prey upon [1-3, 5]. He may have made a habit of hunting slow, squishy humans as a matter of necessity [1-3, 5].

Lion skull with broken teeth
Severe dental trauma of Tsavo man-eater – Photo from Peterhans, Julian, & Gnoske [5]

The second lion had minor dental injuries: two broken teeth, one an old injury and one new [5]. These type of dental injuries are common among wild lions, though, and the researchers didn’t think they were enough to change the lion’s behavior [1, 5]. If the two lions already hunted together, however, the second lion may have taken his friend’s lead in hunting new prey [5].

Field Museum scientists studied the wear and tear patterns on the Tsavo man-eaters’ teeth and concluded that they had not been crunching up bones like wild lions normally do [1, 2]. Their teeth looked more like those of zoo lions [1, 2]. This supports the idea that the two lions were eating a softer diet [2]. But while there is a wide belief that lions and other big cats who eat humans are usually old, sick, or injured, statistically that is not the case [5]. A study in 2014 of the skulls of lions that preyed on humans and/or livestock, a.k.a. “problem lions,” found that most were healthy and in the prime of their lives [5]. Those that were debilitated usually had leg injuries that made it difficult for them to chase down and grasp prey, rather than tooth problems [5].

Cultured Beasts

The idea that non-human animals have their own cultures might seem strange, but many species have been shown to exhibit differences in behavior between subpopulations that can only be explained as knowledge passed through the generations [5]. Tsavo lions have some of these cultural differences that set them apart from neighboring lion populations [5, 7]. The lions of Tsavo live in prides about half the size of Serengeti lions, with only one male and up to ten females [7]. There is never more than one male in the pride in Tsavo [7]. Tsavo lions are also known for preying on humans [5, 7].

Humans may have taught the lions this habit [5, 7]. For centuries, Arab slave traders used the same routes through Tsavo to the port at Mombasa [5, 7]. Along the way, many of the slaves would die from sickness or maltreatment [5, 7]. The dead and dying were left where they fell [5, 7]. Lions are known for being predators, but they will scavenge, too [5, 6]. They likely learned that humans were a good food source by feeding on the bodies of those slaves [3, 5, 7].

Through the generations, the lions remembered that humans are prey. The Kenya-Uganda railway was built along an old caravan path that had probably provided the lions of Tsavo with much human and livestock prey in the past [5]. When thousands of largely unprotected workmen appeared on the path, it may have seemed like a dinner invitation to a pair of young lions.

Changing Environment

Some big changes in the lions’ environment could have prompted them to change their hunting behavior. For one, lions are ambush predators, like almost all felines, so they prefer to hunt from within vegetation or other natural cover [5]. The Tsavo region is especially hot and dry, with the vegetation growing as tangled thornbush called “nyika” [4-6]. The ivory trade significantly reduced the number of elephants in the region by the 1890s, and fewer elephants led to more vegetation [5]. In his book, Col. Patterson describes literally crawling through the nyika looking for the killer lions [4]. These thickets made it easier for the lions to ambush the rail workers [5].

The pair of lions’ interest in the rail workers may have stemmed from environmental changes as well. Since the 1860s, Tsavo had been suffering from severe drought and famine as well as epidemics of cholera and plague [4, 6]. This reduced the population of wild prey, but it also led to large numbers of dead and dying humans left in the wilderness for the lions to eat instead, training them on the new food source [6]. Exacerbating the lions’ plight was a dire epidemic of rinderpest, a deadly cattle disease that also affects many wild herd animals [3, 5-7]. Rinderpest is native to Asia and arrived in Africa in 1887 through infected cattle from India [6]. The first African rinderpest epidemic killed 95% of Ethiopia’s cattle [6]. Buffalo, favorite prey of lions in Tsavo, are particularly vulnerable [5]. With the lions’ usual prey depleted, the switch to humans may have been a simple and practical decision.

Visit the Lions of Tsavo

Author with lions of Tsavo at Field Museum
Selfie with the lions of Tsavo – Photo by author

After killing the Tsavo man-eaters, Col. Patterson skinned them both and turned them into trophy rugs [2]. In 1925, he sold the skins to the Chicago Field Museum, where they were mounted as taxidermy specimens and displayed in a diorama [2, 3]. They are still on display with the mammals of Africa in the Rice Gallery [2]. I’ve been to see them myself, and I highly recommend visiting the Field Museum if you can.

You can also visit Tsavo National Park in Kenya and see the living lions of Tsavo that still roam the same land Col. Patterson’s man-eaters once stalked. It is one of Africa’s largest game reserves, sporting about 675 lions within the ecosystem as well as a wide variety of other wildlife. [7]

Works Cited

  1. DeSantis, L. R. G. and Patterson, B. D. (2017). Dietary behaviour of man-eating lions as revealed by dental microwear textures. Scientific Reports, 7, 904. https://www.nature.com/articles/s41598-017-00948-5
  2. Field Museum. (2018, February 10). Tsavo lions. https://www.fieldmuseum.org/blog/tsavo-lions
  3. Newbart, D. (2004, August/September). Mystery of the man-eating lions. National Wildlife.
  4. Patterson, J. H. (1907). The man-eaters of Tsavo. The Lyons Press: Guilford, CT.
  5. Peterhans, K., Julian, C., and Gnoske, T. P. (2001). The science of ‘man-eating’ among lions Panthera leo with a reconstruction of the natural history of the ‘man-eaters of Tsavo.’ Journal of East African Natural History, 90(1), 1-40. https://doi.org/10.2982/0012-8317
  6. Tomasula y Garcia, A. (2014) The lions of Tsavo: man-made man-eaters. Western Humanities Review, 68(1), 195-200.
  7. Tsavo National Park. (n.d.). Tsavo National Park lions. https://www.tsavonationalparkkenya.com/tsavo-national-park-lions/

Published July 23rd, 2023

Science

Gene therapy may hold promise for cat birth control

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Tabby cat carry her kitten
Image by Rajesh Balouria from Pixabay

Last month, an article was published in Nature Communications by a team of scientists from the Cincinnati Zoo and Botanical Garden, the Horae Gene Therapy Center, and Massachusetts General Hospital [7-9]. They tested a gene therapy injection as an alternative to spaying and neutering for cat birth control, and the results are exciting.

Why do we need cat birth control?

80% of the estimated 600 million domestic cats in the world are strays or feral [4, 9]. Cat overpopulation leads to more disease and greater loss of birds and other small animals from predation [2-6]. Animal shelters become overrun with homeless kittens and cats, and many are ultimately killed. Cats reproduce very quickly, so it doesn’t take long for a few to become a serious overpopulation issue. The only method of sterilization currently available is spay/neuter surgery. It is effective and permanent, but there are drawbacks.

Surgical sterilization has to be performed by a veterinarian at a surgical clinic [2]. It’s an invasive procedure for females, and both sexes are supposed to have a recovery period, including medication [2]. It’s also expensive [2, 6]. Those resources are in short supply, even more so in developing countries [1, 2, 6]. Thus, there has been interest in non-surgical cat contraception for years. Previous attempts have included vaccines targeting the pituitary gland, toxins targeting reproductive cells, and RNA-silencing drugs to shut down the genetic mechanism of conception [1, 3, 5]. All were either ineffective or unsafe [3, 5].

The Alliance for Contraception in Cats and Dogs (ACC&D) was founded in 2000 with the goal of finding a one-time, permanent, non-surgical contraceptive that would help to curb the overpopulation of homeless cats and dogs [1, 5]. ACC&D wasn’t involved in this study, but ACC&D President Joyce Briggs said, “This research is a huge leap—we’re really excited about it” [1, 5]. She also noted that the lead author, Dr. Lindsey Vansandt, is someone they have worked with before on a contraceptive vaccine called GonaCon [1].

The organization that provided the primary funding for the Vansandt research team has a similar goal. The Michelson Found Animals Foundation was founded in 2009 by inventor Gary Michelson [1, 2, 5]. Its goal is also a single-use, permanent, non-surgical dog and cat birth control, although specifically as a marketable product [1, 2]. Toward this end, the Michelson Found Animals Foundation created the Michelson Prize, $50 million (USD) in research funding plus $25 million if successful [1, 2, 5, 7]. So far, they have given out 41 grants [1, 5].

David Grimm, a journalist for Science, explained that it can be very difficult to get funding for this kind of research; most of the money goes toward studying the human body. So the Michelson Prize grants have been a huge boost to searching for a better companion animal contraceptive. [2]

The Experiment

Dr. David Pepin didn’t have his eyes on the Michelson Prize at first, however. Pepin was looking for ways to help women with ovarian cancer preserve their fertility [6-8]. He was studying anti-Müllerian hormone (AMH), sometimes called Müllerian inhibiting hormone (MIS), which made by the ovarian follicles of female mammals [1, 2, 4-8]. An ovarian follicle is a layer of cells around an egg that nourish the egg as it grows and matures.

Pepin was trying to learn more about what AMH does, so he injected an extra copy of the AMH gene into female mice [2, 4, 5]. This technique, sometimes called gene therapy, does not change the native DNA. It adds new, free-floating pieces of DNA into the cells, complete with all the information the cells need to read the “instructions” on the new piece of DNA. Gene therapy has been used to treat genetic diseases in humans, hence the name, but in this case Pepin was using the same procedure for research purposes to see how the mice would respond to high levels of AMH. He was surprised when the mice’s ovaries shrank, stopped producing eggs, and became infertile [1, 2, 4-6].

“We thought, well, this is a very interesting tool, but what can we use it for?” Pepin said [4]. He decided to submit an application for a Michelson Prize grant, and Bill Swanson, Director of Animal Research at the Cincinnati Zoo, happened to review it [1, 2, 4, 5]. Swanson had actually been working on an opposite project, trying to increase breeding in captive big cats [2, 5]. However, the Cincinnati Zoo maintains a research colony of domestic cats, and Swanson thought Pepin’s proposal was a great idea, so a partnership was struck [2, 4, 5].

Diagram of cat birth control experiment
Experimental design – From Vansandt et al. 2023

The study was small, with three groups of only three she-cats each [3-5, 7, 9]. The nine cats were all named after former first ladies: Michelle, Betty, Abigail, Nancy, Dolly, Barbara, Rosalyn, Jacque and Mary [4]. The domestic cat gene for AMH was constructed into a piece of DNA that the cats’ cells could read, and then that piece of DNA, named fcMISv2, was taken up by the harmless AAV9 virus [9]. Viruses are used in gene therapy because they naturally have the ability to insert genetic material into cells. Three cats served as a control group and were injected in the thigh muscle with AAV9 viruses that were empty, no DNA to inject [3, 7, 9]. Three cats were injected with a lower dose of viruses carrying the gene, and the other three received a higher dose [3, 7-9].

The experimental cats’ muscle cells successfully incorporated the fcMISv2 DNA and began to make AMH [9]. According to Pepin, “A single injection of the gene therapy vector causes the cat’s muscles to produce AMH, which is normally only produced in the ovaries, and raises the overall level of AMH about 100 times higher than normal” [7, 8]. Although their AMH levels increased, only progesterone decreased in response [5, 9]. Their other hormone levels remained the same, their hormone cycles were unaffected, and they showed no signs of adverse side effects [2, 3, 5, 7-9].

During two mating trials, two different toms were each introduced to the nine she-cats for four months at a time [3, 5, 7, 9]. All of the cats in the control group mated, became pregnant, and gave birth to kittens [3, 5, 7-9]. Only two of the cats who received gene therapy even allowed the toms to mate, and none of them ever became pregnant or had kittens [3, 5-9]. At the end of the two-year study, they were maintaining steady, elevated AMH levels, and the scientists are cautiously optimistic that this method may be a permanent contraceptive [5, 7-9].

What happens next?

It remains unclear exactly how AMH functions as kitty birth control [1, 2, 5, 9]. The researchers believe that the elevated levels of AMH prevent she-cats’ follicles from developing and thereby prevent ovulation [2-5, 9]. However, more research is needed to understand exactly how AMH works, and to answer lingering questions.

For instance, is this sterilization truly permanent [1, 2, 6]? The scientists who authored the study believe it is, but they only tested those cats for two years, so no one can say for sure yet that it doesn’t eventually wear off. Are there any negative side effects that they didn’t catch in such a small study [6]? Could AMH work for dogs, too [1, 2, 5, 6]? That is an important goal of this kind of research, not to mention a requirement to win the Michelson Prize [1, 5]. There are also concerns about cost, as that is often what prevents people from spaying and neutering cats now [1, 2]. If a new AMH shot will cost as much or more than surgically sterilizing cats, the convenience of the one-dose injection won’t really matter [1, 2].

Pepin, Swanson, and the Michelson Foundation are already in talks with the Food and Drug Administration about a larger trial and the possibility of bringing an AMH drug to market [2, 5, 6], so keep your ear to the ground. In the meantime, GonaCon, the cat birth control vaccine that study author Lindsey Vansandt worked on with ACC&D, has shown promise as well and may actually be closer to becoming available [1]. Either way, this area of study appears to be accelerating, and there may be more exciting news to come in the next few years.

Two kittens peeking through hole in wooden wall
Effective feline contraception means fewer homeless kittens – Image by Sommer from Pixabay

As for the cats from the study, they were all put up for adoption after the research concluded [4]. This is something the Cincinnati Zoo does with their research participants–Bill Swanson already has three cats he adopted from previous studies [4]. I couldn’t find out if all nine have been adopted yet, so if you live in the Cincinnati area and are looking for a new feline friend, email [email protected]. The cats’ new owners are asked to bring them back to the zoo for a yearly check-up to monitor their hormone levels and make sure there haven’t been any side effects [4].

References

  1. Clifton, Merritt. (2023, June 8). No, the wait for a single-shot chemosterilant for cats has not ended. Animals 24-7. https://www.animals24-7.org/2023/06/08/no-the-wait-for-a-single-shot-chemosterilant-for-cats-has-not-ended/
  2. Crespi, S. (Producer). (2023, June 8). Contraception for cats, and taking solvents out of chemistry [Audio podcast episode]. In Science Podcast. American Association for the Advancement of Science. https://www.science.org/content/podcast/contraception-cats-and-taking-solvents-out-chemistry
  3. de Jesús, E. G. (2023, June 6). A gene therapy shot might keep cats from getting pregnant without being spayed. ScienceNews. https://www.sciencenews.org/article/gene-therapy-shot-cats-spay-pregnant
  4. Golembiewski, K. (2023, June 6). Nonsurgical cat contraception could help curb overpopulation, study says. CNN. https://www.cnn.com/2023/06/06/world/cat-contraceptives-scn/index.html
  5. Grimm, D. (2023, June 6). Hello kitty, goodbye kittens? Gene therapy spays cats without surgery. Science. doi: 10.1126/science.adj0979
  6. Katsnelson, A. (2023, June 6). Gene therapy may offer birth control for cats. The New York Times. https://www.nytimes.com/2023/06/06/science/cats-birth-control.html
  7. Ridings, M. (2023, June 6). Birth control for cats? Harvard Gazette. https://news.harvard.edu/gazette/story/2023/06/birth-control-for-cats-is-effective-but-ahead-of-its-time/
  8. Today’s Veterinary Business. (2023, June 19). Gene therapy shows promise in feline contraception. https://todaysveterinarybusiness.com/gene-therapy-0623/
  9. Vansandt, L. M., Meinsohn, M., Godin, P., Nagykery, N., et al. (2023). Durable contraception in the female domestic cat using viral-vectored delivery of a feline anti-Müllerian hormone transgene. Nature Communications, 14, 3140. https://doi.org/10.1038/s41467-023-38721-0

Published July 9th, 2023