Sterilizing, Relocating Wolves Boosted Caribou Herds

STUDY: Infertile animals maintained their former territory and lived longer

Tim Mowry / Fairbanks Daily News-Miner / May 10, 2004

Seven years after biologists sterilized 15 pairs of wolves as part of an effort to rebuild the Fortymile caribou herd, eight of those pairs have at least one wolf remaining and three pairs have both.

Each pair composed its own pack after fertile wolves were relocated, and the eight "packs" remaining are maintaining their traditional territories.

The sterilization program has exceeded biologists' expectations, said Rodney Boertje with the Alaska Department of Fish and Game in Fairbanks.

"We didn't know they'd live this long," Boertje said. "We thought the best we'd get is one or two years out of it."

Wolves in the wild typically don't live to be much over 5 years old, he said. The surviving sterilized Fortymile wolves, however, are all likely pushing 10 years or older.

"Very seldom do you see an 8-year-old wolf," Boertje said. "They get replaced before that because they can't keep up with all the competition they've got out there."

From 1997 to 2000, biologists sterilized the alpha pairs in 15 packs and relocated 140 other wolves that made up those packs. The idea was that the sterilized pairs would defend their territories against other packs, which they have done successfully.

"Four years later, we've still got sterilized wolves functioning as packs," Boertje said.

The project was aimed at reducing predation on the Fortymile herd, specifically at the herd's calving grounds, and the recovery effort has been a success. The herd has more than doubled in size since 1995, with the latest population estimate at 45,000 caribou.

How much of a factor the sterilization program has been in the herd's recovery is a question that biologists are still trying to answer.

"The fact that these pairs have stood up to the test of time is pretty impressive," state wildlife biologist Jeff Gross said. "Some of them are 10, 11 and 12 years old, and they're still holding their territories. The sterilization program "kind of proved itself a real viable management option. It's shown it's got some longevity. It really is a cost-effective means to reduce numbers in the long run."

Biologist Craig Gardner, who helped Boertje start the project, refers to the sterilized pairs as "dinks" -- double income, no kids.

The fact that the sterilized wolves didn't have pups to raise or feed has likely played a significant role in their prolonged survival, biologists said.

"It's the beauty of having no kids and no stress in their life," Boertje said, with a chuckle. "If they're raising pups every year, there's no way they're going to get to 10.

"They're not fighting as much, they're not playing with offspring ... they're just living high on the hog."

Two pairs of sterilized wolves were killed by other wolf packs last year, and Boertje examined the carcasses of those wolves, which he estimated to be 7 or 8 years old.

"They were some of the fastest wolves I've seen," Boertje said. "Even at a very old age they still are able to take care of themselves."

During a tracking flight earlier this winter, Gross spotted one pair of sterilized wolves on a moose kill.

"These pairs are still healthy enough to take down a moose," he said.

The sterilized wolves also don't have to hunt as much because there isn't a whole pack to feed, said biologist Mark McNay, a wolf expert at Fish and Game in Fairbanks. And that cuts down on the chances of being killed while trying to take down a moose or caribou.

About half the wolves that McNay examines have some evidence of previous injuries from killing moose or caribou, such as broken ribs, cracked skulls and broken leg or foot bones.

"Smaller packs kill fewer prey animals, so they're not exposed to the risk of having to kill moose," McNay said. "Those risks can be substantial."

The fact that the sterilized pairs have managed to maintain their traditional territories, even on a slightly smaller scale, doesn't surprise McNay.

"That's what wolves do, defend territories," he said. "They will defend that territory even if they don't have any current pups. They're just continuing to behave as they would if they hadn't been sterilized."

It remains to be seen what will happen when all the sterilized wolves die off, which they probably will do in the next year or two, biologists said. The sterilized pairs likely will be replaced by other packs that move into the territories and kill the older wolves, Boertje said.

There are already signs that other packs are moving in to take over.

"The number of wolves will increase once the sterilized packs die off," he said. "One hypothesis is that there are enough caribou now to support those wolves.

"The other hypothesis is that wolves will get dense enough to bring the (caribou) population down to a lower level."

One of the reasons the biggest caribou herds in the state, such as the 130,000-member Porcupine herd and the Western Arctic herd, which is approaching 500,000, are located on the North Slope is because there aren't as many wolves as there are in the Interior, Boertje said.

"The Fortymile caribou don't have any good place to hide during calving, especially once the sterilized wolves are gone," Boertje said. "It's not coincidental that the Arctic herds go to places to calf where there are no predators."

Regardless of what happens with the herd in the future, Gardner said, the sterilized wolves have more than served their purpose, both biologically and scientifically.

"It proved you can take a pack, reduce it down to two wolves and they have the ability to maintain that territory and keep it at two wolves," Gardner said.

The long-term effect on wildlife populations is still to be determined.

"We're just now starting to put things together," he said.

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