TWS2021: Disease, predation causing Appalachian spotted skunk decline

The Appalachian subspecies of the eastern spotted skunk is facing large declines, likely due to a combination of predation and canine distemper, a disease fatal to the carnivores.

Concerns about the eastern spotted skunk (Spilogale putorius) prompted the International Union for Conservation of Nature to change its status from least concern to vulnerable as it joins a global trend of small carnivores on the decline.

The skunk has three subspecies, each occupying a different regions of the United States. The Florida spotted skunk (S. p. ambarvalis), occupying its namesake state, remains abundant. The Plains spotted skunk (S.p. interrupta), which occurs west of the Mississippi River, is being petitioned for listing under the Endangered Species Act. But researchers haven’t known much about the status of the Appalachian spotted skunk (S. p. putorius), a subspecies restricted to the Appalachian Mountains.

“There’s increasing concern about the Appalachians due to the limited number of sightings over the past several decades,” said Andrew Butler, a PhD student at Clemson University, during a presentation on his spotted skunk research at The Wildlife Society’s virtual Annual Conference. “Up to this day, there have been no previous estimates of Appalachian spotted skunk survival.”

Eastern spotted skunk research in general has been limited, he said. Only two previous studies documented the survival rate of the species. One found that mammalian predation was the largest source of mortality. Butler set out to find out more about its survival rate and to estimate population trends.

To conduct the research, Butler and his colleagues used radio tracking data they collected from four different studies conducted between 2014 and 2020 in Alabama, South Carolina, North Carolina and Virginia.

In these studies, they deployed trail cameras near recent sightings of the skunks so they could trap them and fit them with VHF tracking collars. When the skunks died, the researchers classified the cause of mortality and took note of canopy cover and terrain ruggedness—features that could protect the skunks from predators—as well as other data, like latitude, elevation and whether skunks were juveniles or adults.

Butler and his team found that the Appalachian spotted skunk population was declining by about 0.3% a year. That suggests that remnant populations in these areas are not producing enough recruits to recolonize their historic range. Their survival was 50%—between the survival rate of the Florida and Plains subspecies. Predation was the largest source of mortality, they found, but it wasn’t from mammals. It was mostly predation by avian predators, like owls.

But the causes of mortality differed depending on the study area. In North Carolina, they documented a canine distemper outbreak that killed half the collared skunks and some uncollared skunks in just  days. “This indicates that disease can have a big effect on population dynamics in this area,” Butler said, and their small populations make them particularly vulnerable.

“We suggest that more long-term demographic monitoring occur over a wider land use gradient, such as those areas with more human influence,” he said.

Header Image: There are three subspecies of the eastern spotted skunk. Researchers found a lack of information on how the Appalachian subspecies is faring. Credit: Grayson Smith/USFWS