DNR report lays out causes of deer mortality
In north, predators a major factor, but hunters tops
Feb. 22, 2012
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Hunters killed more adult and yearling deer than any other cause.
Only 27% of fawns survived seven months in northern Wisconsin.
And the buck mortality rate of 50% might cause a significant revision of the state's long-standing method for estimating the deer population.
These are among the findings of the first year of Wisconsin deer research to learn more about fawn survival, study predator impacts on deer and improve the Sex-Age-Kill deer population model.
The report was made public Wednesday by the Department of Natural Resources.
It's titled "Evaluating survival and cause-specific mortality in adult and fawn white-tailed deer in northern and east-central Wisconsin."
Some of the points listed in the report confirm what has long been held, such as hunter harvest being the leading cause of adult and yearling deer mortality in the state.
But others shed light on previously unknown or little-studied facets of Wisconsin's prize big-game species.
"That's the value of boots-on-the-ground research," said DNR research scientist Chris Jacques, the report's lead author. "These projects are giving us an outstanding opportunity to add to our knowledge of deer in Wisconsin."
The work is formally divided into two projects: a buck mortality study and a fawn recruitment and predation study.
Blood and other samples taken from deer in the study will also provide insight into the health of the herd.
Costing more than $2 million, the work represents Wisconsin's largest investment in deer research. The projects are funded through the Federal Aid in Wildlife Restoration Act, an excise tax on hunting and shooting equipment.
Data were collected from late 2010 to December 2011 in two areas: a 3,500-square mile northern forest study area in Sawyer, Price and Rusk counties and a 2,300-square mile eastern farmland study area in Shawano, Waupaca and Outagamie counties.
Researchers captured and placed radio collars on 73 yearling males (45 in the north, 28 in the east), 45 adult males (25 and 20), 86 adult females (40 and 46) and 78 fawns (30 and 48).
If researchers detected a "mortality signal" from a radio collar, they traveled to the site and attempted to determine cause of death.
Among the preliminary findings listed in the report:
Hunter harvest (38%) and predation (26%) were primary sources of adult and yearling deer mortality across northern Wisconsin.
Hunter harvest (61%) and vehicle collisions (24%) were primary sources of adult and yearling deer mortality in the east.
In the north, 22 fawn (13 males, nine females) mortalities occurred through December, representing 73% of the 30 radio-collared fawns. Most (64%) fawn mortalities were attributed to predation; bears and bobcats were the leading predators.
In the east, 18 fawn (11 males, seven females) mortalities occurred through December, representing 38% of 48 radio-collared fawns. Most fawn mortalities were attributed to predation (33%), starvation (33%), and vehicle collisions (17%). Coyotes were the leading predator of fawns in this area.
"Relatively high" pregnancy rates were noted in the north (92%) and east (93.5%).
- Most adult deer (66% in northern and 90% in east) were non-migratory.
- Adult deer that did migrate averaged 3.8 and 2.7 miles, respectively, between seasonal ranges in the northern and east study areas.
Deer ticks (Ixodes scapularis) were present on 23% of deer sampled.
No deer showed exposure to epizootic hemorrhagic disease (EHD), a deadly deer disease, and only 1 to 3% showed exposure to bluetongue and eastern equine encephalitis.
Five adult male deer were poached in northern Wisconsin during 2011.
- At the end of December, 19 adult males, 22 adult females and 8 fawns were "on the air" and monitored weekly for movement and survival status in northern Wisconsin.
- And in the east, 21 adult males, 25 adult females, and 30 fawns continue to be monitored weekly.
More than 200 Wisconsin citizens assisted with 2011 deer capture events.
Though fawn survival has been extensively studied in North America, no information exists on the potential effects of predation on deer recruitment in Wisconsin, according to the report.
Fawns in the north weighed an average of 9.3 pounds, "significantly" less than in the east (11 pounds).
Jacques said the researchers will continue to track fawn weights and habitat conditions. Lower birth weights are often associated with lower fawn survival.
It has always been assumed that hunters kill the most deer in Wisconsin. The study found that to be true among adult and yearling deer.
But in northern Wisconsin, the number of adult and yearling deer killed by predators isn't far behind hunter harvest.
Hunters killed 20 deer (seven adult bucks, four adult females and nine yearling males) in the northern study area, while predators killed 14 (two adult bucks, three adult females and nine yearling males).
Of that total, wolves killed four deer (all yearling males), bobcats three (two yearling males and one adult female), coyotes two (one each adult female and yearling male) and bear one (adult female). The species was not listed on four predator kills due to insufficient evidence.
In the east-central study area, hunters killed 23 deer (seven adult males, six adult females and 10 yearling males). Vehicles were next highest cause of mortality (nine). Predators did not kill an adult or yearling deer in the east-central area.
As stated, predators were far and away the leading cause of death in fawns. In the north, predators accounted for 64% (14 of 22) of fawn mortality. Next leading causes in the north were hunter harvest (14%) and starvation (9%).
Bears killed five fawns in the north, bobcats killed two and coyotes killed one. Researchers could not determine the predator species in the other cases.
In the east-central, predators accounted for 33% (six of 18) of fawn mortality, the same as starvation. The next leading source was vehicles (17%).
Coyotes killed four of the six fawns in the east-central, bears killed one and one kill was listed as unknown predator due to insufficient evidence.
The Wisconsin study is contrasting with work in the Upper Peninsula of Michigan that has shown coyotes as the leading predator on both adult deer and fawns.
Poachers killed five adult deer in northern Wisconsin, the same number as died from starvation and vehicle collisions.
A 2009 DNR document titled "Wolves and deer in Wisconsin" compared various sources of deer mortality in the northern and central forest regions.
It attributed 122,000 deer deaths to hunters and 68,000 to predators (33,000 to bears, 16,000 to coyotes, 13,000 to wolves and 6,000 to bobcats).
In other words, according to the document predators killed 56% as many deer - adults, yearlings and fawns - as hunters.
But that may have underestimated the predator take on deer, especially since it included fawns.
The first year of research in the northern study area shows the predator kill of adult and yearling deer alone to be 70% of the hunter harvest.
If the number of fawns is added, the predator take on deer in the north exceeds that of hunters.
Another area of the report that will draw high interest is related to buck mortality.
A 2006 audit by an independent panel recommended Wisconsin improve its estimates of "buck recovery rate," the proportion of male deer killed by hunters and a key variable used in the SAK deer population model.
The SAK model used by the DNR has assumed a 70% rate for northern and 80% rate for eastern Wisconsin. But the first year of the study found about 50% in both areas.
"Should the overall contribution of harvest to total buck mortality be assumed too high, the resulting SAK estimates will be biased downward," wrote the 2006 review panel.
While this may be difficult for many hunters - who have complained the DNR's deer population estimates have been too high - to believe, the SAK model may be skewed low by inaccurate buck recovery rates.
The report acknowledges the discrepancy between the buck recovery rates used in recent years and the observed rates from the first year of the study.
"We emphasize that our findings are both preliminary and limited to a single year of field data, thus the tendency to draw conclusions based on these data should be interpreted with caution," the report states.
Partners in the projects include the DNR, UW-Madison Department of Forestry and Wildlife Ecology, UW's Applied Population Laboratory, UW-Stevens Point, the Wisconsin Conservation Congress and Whitetails Unlimited.
The buck mortality study is designed to run to 2015. The goal of this project is to improve the accuracy and precision of deer population estimates in Wisconsin. Deer trapping and collaring will continue through the winter of 2014.
The fawn study will run to 2013. It is focused on fawn recruitment and predator effects on fawn survival. Field work will be completed following the fawn capture season in May and June.
In addition to weekly monitoring all radio-collared deer, the researchers are attempting to capture and collar more adult and yearling deer in the study areas through March.
A copy of the full report is posted in the "On the Trail" blog.
Send email to psmith@journalsentinel.
Thought you might find the facts interesting on the real killers of deer . The Wolf is not the problem , never has been..
