Mother Wolves Determine Pack Health
October 11, 2012

Heavy Mother Wolves Determine Health Of The Pack

Michael Harper for — Your Universe Online

After studying the gray wolves of Yellowstone Park for 14 years, biologists have discovered the key to raising happy, healthy, productive wolf cubs.

The secret? Cooperation and a nice, heavy mother.

These gray wolves were reintroduced into Yellowstone National Park in the mid-1990s. Since then, the wolves have been widely studied by biologists and scientists as they work to figure out what makes these carnivorous populations tick. According to Robert Wayne, a professor of ecology and evolutionary biology at UCLA, these wolf packs have turned out to be a great model for the study of sociality and cooperation.

As pack animals, the wolves are very territorial and stick close to their own kind. Female wolves don´t care exclusively for their young, spreading the maternal care around to the whole of the group and providing food to any hungry pups. The females also protect the young against potential predators, such as rival packs. The more protected the pack, the better chance it has of survival. One way these female wolves can help protect their pack is maintain plenty of weight, says Wayne.

“A female´s body weight is key in the survival of her offspring, and cooperation in the protection and feeding of young pups pays off in terms of the production of offspring.”

A larger mother wolf is also better equipped to fight off any encroaching wolf packs, according to Wayne, explaining his research in a recent statement.

“Consequently, larger packs tend to get larger and win the ℠arms race´ of holding territories against the aggressive actions of other packs,” said Wayne.

“Large packs get better at building armies of soldiers to defend their turf, and cooperative behavior and sociality are maintained by natural selection.”

Throughout the many years of wolf-study, former UCLA graduate student Dan Stahler and former UCLA postdoctoral scholar Bridgett vonHoldt analyzed the life history and genetics of some 300 gray wolves in Yellowstone National Park. This pair also studied the way these wolves survived as a pack as well as the way they grew the size of the pack through reproduction. Once again, these biologists found another link between the weight of mother wolves and the overall health of the pack.

“We discovered that mother wolves´ body weight and pack size play a crucial role in enabling pups to survive and thrive from birth to young adulthood,” explained Utah State University assistant professor of wildlife resources Dan MacNulty, who also worked on the study, acting as a co-author.

While the weight of the mother is important to consider when looking at the overall health of the group, other environmental factors are also at play. Factors such as population density, resource availability and diseases can also determine the overall health of the pack.

“Each of these factors effects reproduction, but, overwhelmingly, female body weight and pack size are the main drivers of litter size and pup survival,” said Dan Stahler.

“Bigger females produce bigger litters; bigger packs are better equipped to hunt and defend pups and resources from competitors.”