Death of Breeder Threatens Wolf Pack Survival, Study reveals

When a breeder wolf dies, it's sex and the size of the wolf pack that determines the fate of the pack.

Gray wolves are known to thrive in packs. Turnover among young members of a pack is quite high as they leave in search of mates or start a pack of their own. It is the breeding members that stay with the pack and act as a social glue connecting the members.

And when these breeding members die, the pack might dwindle out, according to researchers at University of Alaska Fairbanks. In 2012, a team of biologists noticed a drop in the number of wolf sightings at the Denali National park following the death of a breeding female from a pack that thrived in that region.

"This isn't the first time we have noticed that the loss of a breeding wolf can affect the fate of the pack. We thought it would be valuable to systematically look at what happens to the pack and population following the death of a breeder," said author Bridget Borg, a University of Alaska Fairbanks biology graduate student and National Park Service biologist.

In this study the biologists looked at changes that occur in a wolf pack following the death of a breeder, its reproduction as well population growth

The researchers observed data of 70 packs of wolves collected from long-term study of wolves in the park as well as the preserve. They noticed that the death of a breeder preceded or coincided with 77 percent of the packs disappearing. In two out of three cases the pack continued, despite the death of the breeder, a rare occurance.

"It appears that the sex of the breeder that was lost and the size of the pack prior to that loss were important factors explaining pack fate following the death of a breeder," Borg said. "The probability of a pack continuing was less if a female died or if the pack was small prior to the death."

But if the breeder died during the pre-breeding or breeding season, then the impact on the pack was severe. However, higher rate of breeder mortality and disruption of the pack did not correspond to the small population growth, suggesting the population of the wolf was resistant to the loss of the breeding mothers at the population level.

By rapid replacement of breeders or increased reproduction in the successive year, the wolves compensated for the death of the breeders.

The finding was documented in Journal of Animal Ecology.