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Mange as Population Control in Foxes

By Kay Wiseman

When was the last time you observed a healthy fox in Colorado?

I moved from the mid-west to Fort Collins, CO in 2011. I work and play in the outdoors so I tend to take notice when nature seems a bit “off.” No sooner had I settled into my new city that I began seeing foxes (Vulpes vulpes) scamper about neighborhoods and green spaces. But something about them just wasn’t right.

They were out in the open in the middle of the day.

They didn’t shy away at the first sign of people.

They looked absolutely dreadful; scrawny, dirty, scabby, tailless.

They were not the foxes I remember from back east. What I soon learned from my colleagues was that I had apparently moved to the Front Range during a major sarcoptic mange outbreak.

Natural systems have a process of checks and balances for populations. Populations generally fluctuate in regular cycles over periods of time. In some instances, a species population can seemingly grow exponentially until it reaches a certain carrying capacity1 and then rapidly decline. If you paid attention in middle or high school science, you’ll remember this as a “J-curve” pattern.

While there are many causal factors that must be taken into account for these declines, one factor that contributes significantly is disease. A species approaching carrying capacity is competing with itself for resources. As resources become scarce, the health of individuals may decline, which increases their susceptibility to disease. For the Front Range foxes, disease came in the form of sarcoptic mange, and to a lesser extent, rabies and West Nile.

Sarcoptic mange is caused by burrowing mites in the Sarcoptidae family. The mites dig through the skin causing intense itching and inflammation. Foxes that have contracted these mites scratch and bite furiously causing skin damage and opening themselves up—very literally—to severe infection. Mange is highly contagious in mammals and can even be transmitted to humans through direct contact. In humans, sarcoptic mite infection is referred to as scabies…gross. Luckily, for humans and our domestic animal friends, there is treatment. Unfortunately for wildlife, nature must take its course.

As much as we complain about the sly fox breaking into our hen houses, these adorable little predators have an important role to play and sadly we never seem to appreciate that role until they’re gone. During the outbreak, the Front Range reported increased rodent populations such as rats (Rattus spp.) and rabbits (Sylvialgus spp.; Lepus spp.), as well as outbreaks of disease carried by rodents. Health departments across the state were reporting human cases of tularemia (rabbit fever), hantavirus, and plague. Without predators, like the fox, the rodent population was not controlled and their numbers skyrocketed exposing people to an elevated risk of disease transmission.

After this 2 to 3 year mange outbreak ended, I no longer observed foxes anywhere along the Front Range. In fact, it was the summer of 2016 before I saw my first healthy fox in Colorado. The fox was beautiful with a sleek red coat and fluffy white tipped tail. Over the next year, I observed multiple frolicking foxes and my face lit up with excitement each and every time. The once devastated fox population is rebounding! Watch your hens everyone!

Photo: Red fox observed in Fourmile Canyon, Boulder County. Photo courtesy of Michael Duran

 

1 The carrying capacity of a population represents the absolute maximum number of individuals in the population, based on the amount of the limiting resource available. An Introduction to Population Ecology – The Logistic Growth Equation. Brandon M. Hale and Maeve L. McCarthy

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