Finding the Fox by Andreas Tjernshaugen

Author:Andreas Tjernshaugen
Language: eng
Format: epub
Publisher: Greystone Books
Published: 2024-04-15T00:00:00+00:00

A Natural Experiment

THE MANGE EPIDEMIC that broke out on the Scandinavian Peninsula while I was a child in the 1970s served as a large-scale natural experiment, and a unique opportunity for scientists to study the fox’s impact on small-game populations.

For the red foxes of Norway and Sweden, mange was a catastrophe that can best be compared with the Black Death that ravaged humanity in the fourteenth century. Fox numbers plummeted by well over half, and the cause was a skin parasite that goes by the Latin name of Sarcoptes scabiei. It is also known as the scabies mite, because a mite is what it is—a tiny, eight-legged relative of the spider. And this particular mite is so tiny that it is barely visible without a magnifying glass. The scabies mite burrows just beneath the outer layer of the skin, then lays eggs, and, as any person who’s ever been infected with scabies can tell you, it itches like hell. Scabies in humans is caused by a variant of the mite that specializes in living in human skin, and which can be transmitted from person to person. This irksome disease has existed since time immemorial. The mite that attacks foxes, however, is a different variant, and it causes a disease known as mange. It specializes in living beneath the skin of foxes and other predatory mammals, and causes only temporary irritation to humans who have come into contact with infected animals.

Fox mange was unknown in Norway and Sweden until the 1970s. As a result, the foxes there had no resistance to the disease, which explains why they were hit so hard when it eventually arrived. The infected foxes developed rashes and matted fur, followed by extensive hair loss, sores, and scabbing. Eventually, they stopped eating, becoming thin and emaciated. In the vast majority of cases, the disease led to death.

BUT EVERY CLOUD has a silver lining—the mange outbreak in the Scandinavian Peninsula offered a unique insight into the red fox’s impact on the species it hunts. The most detailed studies were carried out at Grimsö Wildlife Research Station, which is located in a landscape of coniferous forest and bogland in inland Sweden at roughly the same latitude as Stockholm and Oslo. By the time mange reached this area in 1982, scientists had already been keeping count of foxes and their most important prey for a number of years. Each spring, they would set traps for field and bank voles, check all known den locations to see whether the foxes had had a litter, and record observations of foxes and other game, such as mountain hares, roe deer, and various grouse species—the black grouse, the western capercaillie, and the hazel grouse.

Mange took such a toll on the fox population in the Grimsö area that the impact lasted for the rest of the decade. The number of litters did not recover until around 1990. Populations of field and bank voles, the foxes’ most important prey in this area, turned out to be unaffected.

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