In Yellowstone National Park’s frigid winters, small mites can have a big effect on the wolves they invade, altering the times they hunt, how many calories they need to consume and how far they travel.
The findings were published in the March 28 edition of the scientific journal “Ecology.” Ecologist Paul Cross, of the USGS Northern Rocky Mountain Science Center in Bozeman, was the lead author of the study, which concludes six years of research he has conducted on the topic of mange in wolves using thermal imaging cameras.
“It’s a very complicated paper, highly mathematical, but the gist of it is that when wolves get mange they lose a lot of heat,” said Doug Smith, wolf biologist for Yellowstone National Park.
The mites that cause mange burrow into their host’s skin to feed and lay eggs, causing infections that lead to irritation. As the infected animal repeatedly scratches its irritated skin, its fur falls out. This can be dangerous in the winter when a wolf’s coat does not regrow. Fur loss can be in small patches or as much as a third of the wolf’s body.
With less fur for insulation, a wolf has to modify its behavior.
“If heat is lost it needs to be replaced,” Cross explained. “The way to replace it in warm-blooded animals is to eat more.”
Using images to capture the effects of mange on wolves, Cross calculated that the disease could cost a wolf 60 to 80 percent of its daily caloric budget. Normally, Yellowstone’s wolves burn about 4,000 to 6,000 calories a day while traveling on average 10 miles a day.
“That’s common to animals living in a cold climate,” he said.
To conserve energy, the mangy wolves tended to travel less in a day. The animal with the worst infection did not travel at all during the night, when it would have been colder. That’s contrary to healthy wolves which travel more at night.
“Which is maybe what you would expect if it was trying to conserve heat,” Cross said.
The study also found that although cold weather demands that an animal burn more calories to stay warm, wind had an even more chilling effect.
Previous studies by Cross have shown that wolves living in larger packs are better at surviving the ill effects of mange, possibly because the larger packs can provide enough food to sustain the animals through a tough winter.
The studies have also raised other questions that future research may be able to answer. To feed that increased caloric need, will the infected wolves try to kill more elk, their main food source? Or will they simply stay on a carcass longer and eat it more completely?
One calculation in Cross’ study showed that if eight out of 40 wolves (20 percent) had mange the increase in caloric need would amount to the energy supplied from consuming 12 additional cow elk each winter.
The reintroduction of wolves to Yellowstone National Park in 1995-96 caused a number of effects: elk numbers fell; with fewer elk, waterway vegetation thickened; with more vegetation, beavers recolonized streams.
The effects of a major predator, like wolves, created what’s called a trophic cascade. But what happens when megafauna like wolves become the prey of a much smaller predator, such as the mites that cause sarcoptic mange? Future research might also reveal another trophic cascade with mites as the top predators, Cross theorized. That won’t be an easy task.
“Simultaneous to mange in the park the elk populations were declining, the climate is changing, it’s hard to figure out how much anything is affecting each factor because they are all moving,” Cross said.
Mange was introduced into the Northern Rockies in the early 1900s by the Montana state wildlife veterinarian in an attempt to help eradicate wolves and coyotes. The disease persists in coyotes and foxes. After being reintroduced to Yellowstone wolves were free of mange until 2007.
“It is ironic that a parasite originally introduced to help eradicate wolves may increase their effects upon prey populations a century later and is potentially one more in a long list of unintended consequences in wildlife management,” the “Ecology” paper stated.
Mange in pack
This year, the park’s Lamar Canyon pack is the only one infected with mange but all five of the adult wolves have the disease and it is believed to have played a role in the death of all of the pack’s six pups, Smith said.
“There are other complicating factors, but it wouldn’t be this bad without mange,” he added.
As the Lamar Canyon pack comes into contact with nearby wolves, Smith now wonders how long it will be before other packs are infected.
The most recent counts of Yellowstone’s wolves show there are 79 wolves in 10 packs, down from 99 wolves at the end of December.
“That’s very typical,” Smith said, as wolves without collars move across the landscape and disappear. Pups will be born in April, once again boosting the park’s wolf population.
“The message is they seem to have the same number of pups every year,” Smith said. “The big question is how many live? Wolves die at a large rate so you need to have good wolf production for the pack sizes to remain stable.”