Tuesday, November 12, 2013

Do Wolves Take As Many Deer As Some WI Hunters Believe?

October 21, 2013

Q. Do Wolves Take As Many Deer As Some WI Hunters Believe?

A, Barely.

One justification for the Wisconsin wolf hunt and its escalating 'harvest' quotas  - - and escalating kills - - has been the impact some people alleged that wolves have on Wisconsin's deer herd, with some hunters believing that wolves kill too many, leaving the hunters bereft of targets.

gray wolf
Courtesy of the U.S. Fish and Wildlife Service


One hunting guides' website disagreed: 
One gentleman I met from Pittsville [told] a frightful story of a pair of gray wolves circling his hunting party with in 45 yards as they gutted a freshly killed deer. Another story from the registration station told a fable of over 2 hours spent tracking a deer to find the hind quarter half eaten. So it must be the wolves that are to blame right?
Wrong- The wolves may reduce the population some but if you ask me it's the hunters...
According to the Wisconsin DNR, "Each wolf kills about 20 deer per year. Multiply this by the number of wolves found in Wisconsin in recent years (630), and approximately 13,000 deer may be consumed by wolves annually. 
This compares to over 40,000 deer hit by cars each year, and about 450,000 deer shot annually by hunters statewide. Within the northern and central forests where most wolves live, wolves kill similar numbers of deer as are killed by vehicles (about 13,000), and about 1/10 of those killed by hunters (127,000 in 2008). Wolves are a factor in the deer herd, but only one of many factors that affects the total number of deer on the landscape" 
And a DNR publication discussing research to begin in 2010 also threw cold water on the notion that wolves take deer from hunters:

Some hunters argue an expanded wolf population, in particular, has resulted in fewer deer in the northern and central forests.  
Review of published research and preliminary data analysis suggests bears are having a small but measurable impact on fawn mortality and that wolves have a small impact on the mortality rate of adult does.
And you will see the same belief again debunked during a discussion of DNR research recorded at the agency's Wolf Management advisory committee's most recent meeting in Wausau, on July 18 (the bold-facing is mine):
Dan Storm (WDNR Science Services) – Survival and cause-specific mortality of white- tailed deer in Wisconsin (PowerPoint).The study is looking at both fawn mortality & buck mortality in 2 study areas, one in northern WI near Winter & one in eastern WI near Shiocton.  
The study is attempting to estimate annual survival rates, determine when mortalities occur and which mortality causes are most important, and whether survival rates and mortality causes differ between study areas and years. 
- Overall, survival to fall is high (~80%) - Fawn survival – sto In the east is ~60%, with most mortality occurring in the 1 month and starvation & coyotes being the most important causes. 
  In the north is 20-60% (more variable), with predation by bear, bobcats, & canids being the most important cause (not sure how much is scavenging as opposed to predation; they have yet to find a fawn definitely predated by wolf in summer). 
  High annual variability in fawn survival probably has to do with variations in green-up timing (hiding cover), doe condition, & availability of alternate foods for predators. 
Females >6 months - survival is ~80% - Yearling maleso Survival is 60-80% until fall (variable between years); annual survival is ~40% with hunting being the most important cause of mortality. 
o Yearling buck survival is lower & more variable than for older deer; they are more vulnerable to predation & starvation, especially in the north.-  
Adult males 
o Survival is ~85% until fall, with little annual variation. 
o In the east, hunting & road kill are the most important causes of mortality,with predation & starvation being rare. 
o In the north, hunting & winter kill are the most important causes of mortality. Winter kill is primarily canid predation and/or starvation. 
There was discussion of whether the effect of wolves is underestimated because little identifiable evidence is left from wolf predation. 
Even if you assumed unknowns in the study were due to wolf predation, the impact would not be large. Hunter harvest is by far the largest cause of deer mortality. 
There would be little impact on the deer population from reducing the wolf population. Interaction among predator species may limit the effect that decreasing one species will have on the deer population. 
If the wolf population decreases, the coyote population will likely increase, resulting in little change in impact on the deer population. 
The reproduction rate needs to be considered along with the survival rate in order to determine whether a population is increasing.
In other words, hunting, road kill and winter - - not wolves - - are the major factors that reduce principally reduce deer herds.