Sunday, December 07, 2014
What Happens When A Breeding Wolf Is Killed
“Lethal Control of Wolves Provides No Benefit to Livestock”
“Why A Ravening Wolf is a Sheep’s Best Friend”
Those were the headlines yesterday, as media outlets continue to hype a flawed Washington State University research paper that I panned over on Wolf Watch. The WSU researchers noted that through a certain time period:
1) the wolf population increased;
2) livestock depredations by wolves increased; and
3) control (killing) actions wolves to limit livestock depredations increased.
The WSU paper concluded that it was the increase in wolf control that caused the increase in livestock depredations (rather than the very large increase in the number of wolves).
Reminds me of the Ice Cream Murders which found that large cities have increased murder and violent crimes during hot months. During the same time period, sales of ice cream skyrocket. Does this mean ice cream turns people to murder?
Looking for a diversion, I checked my social media feed and found numerous posts about how killing wolves only increases the population when one of a pack’s lead wolves is killed, disrupting the pack’s social structure and making way for more members of the pack to breed. So, you silly ranchers, if you want to save your sheep, don’t kill wolves. Argh!
That someone would believe this stuff makes me crazed. If you’ve got wolves killing your sheep, often the only way you are going to stop it is to kill the wolf/wolves doing the damage – or remove your livestock. The wolves won’t have some Kumbaya moment by the light of the moon that turns them into vegetarians instead of meat eaters.
It’s time to review what is actually known about the effects of the loss of a breeding wolf from a wolf pack – not theory, not modeling, but what has been documented. This issue was addressed in a paper in the Journal of Wildlife Management in 2008: “The Effects of Breeder Loss on Wolves,” written by Scott Brainerd and 18 contributors. The Brainerd paper summarized nearly 150 records of breeder loss in wolf populations around the globe from 1970-2003 and found:
• Wolves reproduced within territories the season after breeder loss in about 47% of cases. (Less than half.)
• Breeders were more likely to be replaced within 12 months where breeders of one sex remained (60%) than where breeding pairs were absent.
• After a breeder loss, if the pack doesn’t reproduce the next season, the pack size is smaller than if the pack does reproduce. (Yes, this is a duh).
• The ability of wolves to reproduce the season after breeder loss was greater in cases where one breeder had to be replaced, than in cases where both breeders had to be replaced.
• The average time it takes for breeder replacement differs with the size of the wolf population. Recolonizing populations with less than 75 animals take an average of 19 months for breeder replacement, while populations with more than 75 wolves take just over 9 months. Average times to next reproduction were 22 months in small wolf populations, and 12 months for larger recolonizing populations.
• In 38% of cases, wolf packs dissolved and abandoned their territories after breeder loss, leaving territories vacant or occupied by solitary wolves. Of these dissolved groups, 53% became reestablished when occupied by new wolves, or when the remaining solitary wolves found new mates. In 21% of cases, neighboring wolves usurped vacant territories. When the cases in which neighboring packs usurped territories were excluded after breeder loss, wolves became reestablished in territories after an average time of 2.72 years.
Montana State University researchers Scott Creel and Jay Rotella co-authored a 2005 paper on human-caused mortality and wolf population dynamics (entitled “Meta-Analysis of Relationships between Human Offtake, Total Mortality and Population Dynamics of Gray Wolves”) that examined 21 North American wolf populations and the relation between total annual mortality and population growth to annual human offtake. The paper noted that the Northern Rocky Mountain wolf population increased 15-fold over the preceding 15-year period. The paper’s findings “reinforce the expectation that harvesting is not likely to increase reproduction or decrease natural mortality by reducing competition for resources.”
The complexity of breeder loss on social structure was also revealed in “Impacts of Breeder Loss on Social Structure, Reproduction and Population Growth in a Social Canid,” by Bridget Borge and three co-authors (including Brainerd), published in July 2014 in the Journal of Animal Ecology. These researchers examined a 26-year dataset of 387 radiocollared wolves in Denali National Park and Preserve, Alaska. Borge, et. al, concluded: “The importance of individuals to the dynamics of populations may depend on reproductive status, especially for species with complex social structure. Loss of reproductive individuals in socially complex species could disproportionately affect population dynamics by destabilizing social structure and reducing population growth. Alternatively, compensatory mechanisms such as rapid replacement of breeders may result in little disruption. The impact of breeder loss on the population dynamics of social species remains poorly understood."