LOGAN -- Mama wolves get by with a little help from their friends.
Or, stated more precisely, mother wolves are more able to raise offspring to self-sufficient adulthood if the females are part of a larger pack, more capable of defending defenseless pups. And it also helps if the mamas are large and healthy.
That's the latest finding from an ongoing study of wolf populations in Yellowstone National Park.
"Using 14 years of data from the long-term study of wolves in Yellowstone National Park, we examined a number of key traits that allow wolves to overcome environmental stress," said Dan MacNulty, assistant professor in USU's Quinney College of Natural Resources. "We discovered mother wolves' body weight and pack size play a crucial role in enabling pups to survive and thrive from birth to young adulthood."
MacNulty is conducting his wolf research with Dan Stahler and Doug Smith of the National Park Service's Yellowstone Wolf Project, and with Robert Wayne and Bridgett vonHoldt of the University of California, Los Angeles. The scientists published their findings this month in the online edition of "Journal of Animal Ecology." Their study is funded by the National Science Foundation, National Park Service and the Yellowstone Park Foundation.
Factors that impact wolf reproduction include the prevalence of disease, especially deadly canine distemper, to which pups are especially vulnerable, and the availability of resources, which can be effected by weather extremes and population density.
Other factors in successful reproduction include maternal age and maternal fur color (gray or black).
"Each of these factors affects reproduction but, overwhelmingly, female body weight and pack size are the main drivers of litter size and pup survival," said Stahler, the study's lead author. "Bigger females produce bigger litters; bigger packs are better equipped to hunt and defend pups and resources from competitors."
MacNulty said gray wolves reproduce and raise their pups to self-sufficiency better than do black wolves. MacNulty believes the genetics that produce a black coat are linked to other genetic factors, such as black wolves' lower level of the "stress hormone" cortisol, for example. MacNulty said he knows of no evidence that actual fur color makes black wolves less successful. MacNulty also said black fur is an indicator that wolves have a domestic dog in their ancestry.
MacNulty said wolves are social carnivores, who work together to kill their food and to protect their young. A larger pack means more food and protection to the young, until that point when the group size is too large for the resources available in their territory.
Another example of social carnivores is lions, MacNulty said. Female lions gather their cubs into a group protected by all the females, and will fight off strange males who are not part of the group, who seek to kill the cubs.
Wolves from competing packs also will attempt to kill young that are not theirs, MacNulty said.
"With wolves, what they have to fear is rival packs," MacNulty said. "We've had instances of rival packs raiding the dens of resident packs. Bigger packs are better at protecting their turf, and that has a direct effect on pup survival. And if a rival pack pushes the resident pack outside its territory, fewer prey are available, and they have a harder time feeding."
MacNulty also said female wolf fertility begins to decline around age 5, which is the median age to which wolves in the wild live.
"There are individuals out there that live to 13 or 14, but they tend to be pretty rare," MacNulty said. "Wolves have what we refer to as a fast life history. They develop quickly. At 1, they have achieved 80 percent of their body weight. They learn how to kill and can reproduce in a very short time. If they are going to pass on their genes to the next generation, they don't have time to develop slowly or learn slowly. They come and go pretty quickly."
MacNulty said people tend to see wolves either as nature's super heroes, able to quickly restore environments to a perfect wild balance, or as one of nature's most menacing, invulnerable villains.
"Wolves are neither of those," he said. "They are not heroes or monsters. The truth is really in the middle."