Healthy mom with lots of help key to thriving brood, scientists say

Oct 09, 2012
Yearling littermates engage in a game of chase in Yellowstone's Druid Peak pack. Credit: Dan Stahler/NPS

(Phys.org)—What does it take to raise successful, self-sufficient offspring? A healthy mom with lots of in-house help, says Utah State University researcher Dan MacNulty. While this advice may benefit humans, a recent study by MacNulty and colleagues actually focuses on another group of large, social mammals – namely, wolves.

"Using 14 years of data from the long-term study of in Yellowstone National Park, we examined a number of key traits that allow wolves to overcome environmental stress," says 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 ."

With Dan Stahler and Doug Smith of the National Park Service's Yellowstone Wolf Project, as well as Robert Wayne and Bridgett von Holdt of the University of California, Los Angeles, MacNulty published findings in the Oct. 9, 2012, online edition of the . The study, which stems from a newly established collaboration between the wolf project and USU, was funded by the National Science Foundation, National Park Service and the Yellowstone Park Foundation, along with private donors.

Environmental conditions that impact wolf reproduction, the researchers say, include disease prevalence, especially deadly canine distemper – caused by a contagious virus to which pups are especially vulnerable; resource availability and population density. In addition to body weight and pack size, the researchers examined effects of maternal age, color (gray or black coat) and wolf population size on reproductive success.

"Each of these factors affects reproduction but, overwhelmingly, female body weight and pack size are the main drivers of litter size and pup survival," says 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."

This video is not supported by your browser at this time.

Social carnivores, wolves live in territorial, kin-structured packs. Female wolves depend on other adults in the pack to help them provide food for their pups and defend the youngsters from predators; mainly, competing packs of wolves.

"Motherhood is a challenge for any species," Stahler says, "But the evolution of cooperation in wolf societies is a notable benefit to mother wolves."

As wolf management in the United States moves from recovery to a new era of conservation, the researchers believe knowledge of reproduction will help managers maintain . With the recent de-listing of gray wolves in Wyoming, state managers assume control of the last federally protected group of these animals in the Northern Rockies this fall.

"While these animals are no longer protected under the Endangered Species Act, states are required to maintain a minimum number of wolves and breeding pairs to prevent re-listing," MacNulty says. "As in Idaho and Montana, Wyoming is legally required to maintain a statewide population of at least 100 wolves, including 10 breeding pairs."

A breeding pair, he says, is defined as an adult male and female with at least two pups surviving to the end of the calendar year.

He adds the Yellowstone study highlights factors that determine the number of pups surviving to the end of the year, and this information may help state managers meet population objectives.

"Managers could use information on pack size, weight of harvested female wolves, or as indicators of future population growth and set harvest limits accordingly," MacNulty says.

If pack sizes are small, female wolves are underweight or disease outbreaks occur, he says, managers could reduce harvest to ensure sufficient numbers of breeding pairs. On the other hand, if pack sizes are relatively large, female wolves are at healthy weights and acute diseases are absent, managers can have confidence that current harvest levels are appropriate.

"Biologists and managers have long recognized the resiliency of wolves," Stahler says. "Our findings point to traits that help explain wolves' ability to overcome environmental challenges like human exploitation or competition with other wolves."

While these findings are specific to the unexploited population, they may well represent important biological drivers of reproduction in any wolf population, he says.

"Long-term, detailed studies from wild ecosystems like Yellowstone's enhance our knowledge about these charismatic, but controversial carnivores," Stahler says. "This type of research has great value in informing anyone who has an opinion about wolves."

"Our results should reassure wolf conservationists," MacNulty says. "If female body weights are high and pack sizes are sufficiently large, wolves can successfully reproduce despite the impact of environmental factors, such as disease and competition."

Explore further: US charges safari owners with illegal rhino hunts

Related Stories

Wolf hunting strategy follows simple rules

Oct 28, 2011

(PhysOrg.com) -- A new study of wolves (Canis lupus) has found that communication between pack members and a social hierarchy are not essential features of a successful hunt, and all the wolves have to do ...

Strength in numbers? For wolves, maybe not

Sep 29, 2011

(PhysOrg.com) -- Watching a pack of wolves surround and hunt down much larger prey leaves most people with the impression that social predators live in groups because group hunting improves the odds of a kill. ...

Feds want wolves taken off endangered list

Feb 02, 2006

The U.S. Fish and Wildlife Service was expected to issue a proposal Thursday removing gray wolves in the northern Rockies from the Endangered Species List.

Recommended for you

How can we help endangered vultures?

19 minutes ago

Zoologists from the School of Natural Sciences at Trinity College Dublin are proposing an ingenious idea to help conserve populations of African white-backed vultures. The iconic birds, which play a critical ...

Scientists work to save endangered desert mammal

59 minutes ago

Amargosa voles, small rodents that inhabit rare marshes of the Mojave Desert, have faced dire circumstances in recent years. Loss of habitat, extreme drought and climate change brought this subspecies of ...

Sex-loving, meat-eating reptiles have shorter lives

2 hours ago

The health risks and benefits of vegetarianism have long been discussed in relation to the human diet, but newly published research reveals that it's definitely of benefit to the reptile population. That, ...

US charges safari owners with illegal rhino hunts

14 hours ago

Two South African men were charged Thursday by the US government with conspiracy to sell illegal rhinoceros hunts to American hunters, money laundering and secretly trafficking in rhino horns.

User comments : 0