By Dr. Becker
Spotted hyenas, sometimes called laughing hyenas, are remarkable for a number of reasons. They enjoy a long life, often living for 20 years in the wild, despite living a hunting-and-scavenging lifestyle that exposes them to a broad array of pathogens.
Spotted-hyena immune systems have become an area of scientific interest, in fact, because these intelligent, socially complex creatures have a knack for avoiding or surviving diseases that wipe out their nearby competitors.
Spotted Hyenas' Are Remarkably Resilient
Rabies? Despite evidence that they're frequently exposed to this typically fatal virus (at least in the wild), spotted hyenas are no worse for the wear, showing no symptoms of the disease and no decreased survival upon infection.1
Anthrax and canine distemper virus also do little to phase these hardy animals, which have also shown extraordinary resilience in recovering from broken bones, lion attacks and even open, festering wounds caused by hunting snares.2
It's believed that some of spotted hyenas' immune resilience comes from their carrion-feeding ancestors.
According to a study published in Veterinary Immunology and Immunopathology, "Theory predicts the immune systems of animals specialized for scavenging should have been molded by selective pressures associated with surviving microbial assaults from their food."3
In the modern day, however, it's known that spotted hyenas hunt at least half of their food supply, which means their reputation as "lowly" scavengers isn't entirely true (and at least one zoologist observed that lions were more likely to scavenge hyena kills than vice versa).4
So it's likely that something else is contributing to their stellar immune response, and this "something" may have been revealed by University of Tasmania and University of South Australia researchers.
Social Status Likely Leads to Higher Levels of Disease-Fighting Antibodies in Female Hyenas
Overall, hyenas must have high levels of disease-fighting antibodies in order to stave off disease, but female hyenas, which are socially dominant in the species, tend to have even higher levels than males, according to the study.5 Their bodies were also better equipped to fight off bacterial infections.
The researchers noted that female spotted hyenas have higher complement-mediated bacterial killing capacity (BKC) as well as two other measures of immune defense than males, which they suggest is due to the females' higher-ranking social status.
Female spotted hyenas are larger and more aggressive than males, and the female hyena's genitals even resemble the male genitals, making it difficult to differentiate between the sexes.
In hyena society, the alpha female eats first, followed by other females and then, typically, males. This increased access to resources, as well as having to expend less energy and risk (like injury) to find a meal, affords them ample energy reserves they can use to fight off infection and disease.
The finding is similar to research conducted in humans, which has also linked social standing to better immune function. Evolutionary ecologist Marion East at the Leibniz Institute for Zoo and Wildlife Research in Germany, who co-authored a study showing hyenas rarely suffer consequences of rabies infection, told Smithsonian:6
"There are several medical studies on humans that clearly show that individuals holding high social status in human societies are healthier in general and have better values in several standard tests of immune function …
Furthermore, several studies show that the outcome of infectious diseases is more severe in humans of low status than those of high status."
Are Hyenas More Closely Related to Cats or Dogs?
If you go by appearance alone, you may assume that hyenas are related to dogs. In fact, they're more closely related to cats. Along with other cat-like carnivores, hyenas are members of the suborder Feliformia.
This is but one common misconception about these animals. While spotted hyenas may be called laughing hyenas, they actually don't laugh.
Their "laughing" is a distinctive call used to express excitement, nervousness or submission. Spotted hyenas also communicate with other members of their group (known as a clan) using at least 10 other vocalizations.
Further, as mentioned hyenas are not only scavengers. They are skilled hunters who work together to take down wildebeest and antelope. They also eat birds, lizards, snakes and insects. National Geographic expanded:7
"Spotted hyenas have good hearing and sharp eyesight at night. They are fast and can run for long distances without tiring.
Packs work together effectively to isolate a herd animal, sometimes one that is ill or infirm, and pursue it to the death. The victors often squabble over the spoils, either among themselves or with other powerful animals like lions."
Many are surprised to learn that hyenas have large brains are quite intelligent. They cooperate, recognize the rank of others in their clans, use a range of tactics when attempting to solve man-made puzzle boxes and can even count.8
Spotted hyenas are not considered endangered, but they are having increasingly common run-ins with humans as Africa's population grows.
According to National Geographic, hyenas are known to raid food stores and crops and have been blamed for livestock, and even human, deaths. As a result, "In some areas they have been heavily hunted as destructive pests."9
In reality, hyenas, far from being nuisances, may one day help scientists uncover the secret to their seemingly indestructible immunity and perhaps harness it to fend off human diseases as well.