Human Voices More Terrifying to Australian Marsupials Than Other Apex Predators

The human voice is terrifying to animals, including marsupials.

Human Voice Terrifies Australian Marsupials

Numerous studies conducted in the Northern Hemisphere have found that human sounds are more scary than those of other apex predators. A new study conducted in the Southern Hemisphere has reached the same conclusion.

When Australian marsupials were tested in Tasmania, the sound of human voices was at least 2.4 times more likely to cause them to run than the sound of any other predator.

Ecologist Katherine McGann of the University of Tasmania and colleagues noted in their research, "Wildlife worldwide evidently recognize that it is humans who are the largest source of danger."

McGann and colleagues were interested in seeing if human voices also caused the greatest dread in mammals that haven't evolved alongside many huge animals since last year. Researchers found that mammals on the African savannah fear human sounds even more than lions.

Because some Australian marsupials exhibit silent or nonexistent reflexes to Northern Hemisphere predators such as foxes or dogs, they are considered predator-naive. This has enabled invading predators to terrorize many weaker species.

For example, the tammar wallaby (Notamacropus eugenii) does not respond to the sounds of dingoes; it only reacts to their sight. According to ethologist Daniel Blumstein and colleagues, this could be because predators' visual cues are more recognizable than their vocalizations. For improved depth perception, all predators, for instance, have eyes that face forward.

The lack of major mammalian predators on the Australian continent for the past 50,000 years has been cited as the reason for the naiveté of Australian marsupials towards predators. However, these findings ignore the existence of people. Per McGann, this is an excellent example of what has long been a very common error in ecology -- failing to acknowledge or consider the role of humans as predators.

Thus, the researchers played the noises of sheep, dogs, Tasmanian devils, wolves, and humans for wild kangaroos, wallabies, pademelons, and possums. The sound of humans caused the marsupials to flee 2.4 times more frequently in 684 recordings that captured their reactions to exposure than the species they reacted to the second most, which was dogs.

Even though they had the lowest chance of running away, brushtail possums showed alertness by rising on their hind legs.

Human Sounds Bring More Terror to 95% of Wildlife Species That Lion's Growling

Lions ought to be the most fearsome land predators since they are the largest group-hunting predators on the planet. However, in another study of 10,000 recordings of wildlife from the African savannah, 95% of the species responded markedly more scared when they heard the sound from humans.

Ecologist Liana Zanette of Western University and her colleagues played different vocalizations and sounds into waterholes in the Greater Kruger National Park of South Africa to see how the animals reacted. This protected area has the largest lion population still alive (Panthera leo); therefore, other species are aware of the threat these carnivores pose.

In addition to recording gunfire and dog barking typical of human hunting, the researchers also recorded human speech in Tsonga, Northern Sotho, English, and Afrikaans. The researchers also played the sounds of lions interacting—snarling and growling. Lions' vocalization is similar to humans having a conversation.

The researchers noticed that nearly all 19 of the studied animal species were twice as likely to leave the waterholes when they heard human voices compared to the sound they heard from lions or hunting predators.

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