The detection of chronic wasting disease in wild white-tailed deer in 2016 created a need for the DNR to understand the ways the disease may spread across the landscape through natural movements of deer.
Three types of deer movement may result in disease spread across the landscape: dispersal events, seasonal movements and temporary excursions.
- Dispersal, or one-way movement from where a deer was born to where it lives as an adult, happens when deer are about 1-year-old and is usually the furthest movement deer make.
- Seasonal movements include migratory behavior and movements between summer and winter ranges (something we commonly see in deer in northeastern Minnesota).
- Excursions are temporary movements that deer make outside of their home range and might be due to looking for food or mates. For this study, we are most interested in long distance movements like dispersal because these movements potentially spread disease further.
This study looks at natural deer movement to learn about potential pathways of CWD spread by infectious deer. The study area is a 30-mile buffer around Preston, Minnesota, where CWD was found in wild deer in Minnesota in 2016. Deer are captured by deploying nets from helicopters and are then fit with GPS collars that give us data showing how they move on the landscape, including what corridors they use (for example, what drainages they follow) and how far they travel. Movement data will be used to inform future disease management decisions.
During the first year of the study in 2018, a total of 109 deer were outfitted with GPS collars. In 2019, 64 deer were added to the study. We classify deer ages as: fawns (less than 1 year of age), yearlings (between 1 and 2 years of age), and adults (greater than 2 years of age). To date, none of the collared deer retrieved in this study have tested positive for CWD.
- August 2019
The spring dispersal period for the fawns collared in February extended from about April 15 through July 15, 2019.
Preliminary results show that about half of the fawns in spring 2019 made one-way long distance movements: 15 out of 34 does and 10 of 22 bucks. The median (or midpoint) straight-line dispersal distance was almost 6 miles (n=15) for does and about 7 miles (n=10) for bucks.
Both the rates of dispersal and the median dispersal distance are comparable with those of 2018. For comparison, we saw nine of 20 does and 10 of 31 bucks disperse in 2018 with a median distance traveled of 7.5 miles (n=9) for does and 7.7 miles (n=10) for bucks.
Given the small sample sizes, we cannot make strong conclusions about differences between sexes or years, but the patterns emerging are very interesting. For both does and bucks we have observed a few animals traveling extreme distances compared to the rest. The extreme travelers skew the averages, which is why it is better to report the median distance traveled. In 2018, the range (minimum and maximum) of dispersal distances by does was between 2.5 to 77 miles, while for bucks it was about 3 to 23 miles. This year, 2019, the range of dispersal distances for does was between about 3 to 29 miles, and for bucks it was about 2.5 to 54 miles. At this point, we don’t know why certain deer choose to disperse long distances from where they were born.
As of Aug. 10, 2019, of the 173 deer that have been GPS-collared and released since March 2018, 66 animals remain available for tracking via GPS. There have been 45 known mortalities due to hunter-harvest (n=14), poor health (n=6), vehicle collisions (n=5), agency culling (n=4), unknown cause (n=4), and capture-related issues (n=12). A significant number of collars from the 2018 release cohort stopped working (n=80) due to either hardware malfunction or collar expansion failure. The manufacturer corrected these issues and there has only been one collar failure to date from the second release cohort of 64 GPS collars.
- March 2019
From September through December 2018, most of the fawns collared that year were expected to have set up an adult home range. Using data from the available deer in the study, we found that 36 percent of does (n=4/11) and 15 percent (n=4/26) of bucks underwent excursions (linear movements greater than 2.5 miles) from their adult home range. On average, does traveled 3.7 miles and bucks traveled about 12 miles. So, although does had a higher likelihood of making excursions from their home range, they traveled a shorter distance on average compared with bucks.
From Feb. 18-21, 2019, we captured and outfitted 64 additional deer with GPS collars: 39 doe fawns and 25 buck fawns. See below for an updated study area map to view where these deer were captured and collared.
- September 2018
During the first year of this study, the DNR captured deer in March 2018 by launching nets from a helicopter and collaring 83 fawns (49 bucks and 34 does), 25 adult bucks and one adult doe.
Based on preliminary analysis of the data from March through April 2018, the average home range size was 0.60 mi2 for doe fawns, 0.88 mi2 for buck fawns, and 1.14 mi2 for adult bucks. These home range estimates align with our expectations of deer activity at this time of year.
During the spring dispersal period from mid-April through mid-July 2018, 32 percent (n=10/31) of buck fawns and 45 percent (n=9/20) of doe fawns dispersed from their birth range. The longest movement measured so far is that of a doe fawn that traveled approximately 77 linear miles (June 2018) from where she was collared. The average dispersal distance traveled for doe fawns was 17.4 miles (n=9) and 10 miles (n=10) for buck fawns.
When we remove two outliers (does that traveled a linear distance of 40 miles and 77 miles, respectively), the average dispersal distance for does declines to about 5.6 miles. During spring 2018, only 17 percent (n=2/12) of collared adult bucks moved greater than three miles from their winter range.
Current collar statistics [Updated 8/10/2019]
|Age & gender||Number being tracked|
As of Aug. 10, 2019:
- 23 deer have slipped free of their collars.
- 83 collars have been deactivated due to expansion or hardware issues. Some of these deactivated collars remain on deer.
- 45 collared deer have died. Hunters legally harvested 14 of those deer, four were harvested by USDA targeted agency culling, and five were likely killed by vehicles.
- Study details
Seasonally, there are two periods of the year when deer are likely to move long distances. The first dispersal period spans between April and July when adult does have their fawns. During this time, adult does may act aggressively toward last year’s young, causing them to disperse to new areas.
A second period of dispersal occurs in the fall during the rut when aggression toward subordinate bucks causes them to move in search of a new home range.
The GPS collars have a battery life of about two years and will provide researchers with deer locations 6-25 times a day. Each deer will be tracked for as long as the deer survives or the collar keeps transmitting. When a deer's collar stops moving for 12 hours, it notifies DNR staff who will respond quickly. We'll try to find the deer as soon as possible so that tissue samples can be gathered for disease testing and a cause of death can be determined. The mortality information will help inform Minnesota's deer population model.
Hunting is a normal cause of deer mortality, and hunters are encouraged to treat collared deer like any other deer. If you harvest a GPS collared or ear-tagged deer, please call 507-380-1858.
How will the study information be used?
The study, which is funded by Minnesota’s Environment and Natural Resources Trust Fund, is planned to continue for at least two more years. DNR scientists in Minnesota plan to share information about deer movements with colleagues in Iowa, Michigan and Wisconsin. With that information, research and management strategies can be developed that will have a better chance of slowing the disease spread and benefit the long-term health of white-tailed deer.
- Study area
Locations where deer were collared
This study is focused on deer movements in and around the CWD management zone in a 30-mile buffer centered on Preston, Minnesota. Click the map above to expand it or view an even larger map in a new browser tab. Because much of southeastern Minnesota is private land, DNR researchers are grateful to the landowners who granted access to about 72,000 acres for collaring deer in February 2019.
Locations where deer were collared
This study is focused on deer movements in and around the CWD management zone, deer permit area 603. Click the map above to expand it or view an even larger map in a new browser tab. Because much of southeastern Minnesota is private land, DNR researchers are grateful to the landowners who granted access to nearly 68,000 acres for collaring deer in March 2018.
- Movement maps
- Overview map
Where are collared deer moving?
This map shows the movement of deer in the study between March 2018 and July 2019. Each color represents a different animal. This maps displays 148 deer who were in the study for 30 or more days. As of August 2019, only 66 animals remain in the study. Click the map above to expand it or view an even larger map in a new browser tab.
- Deer 157
This map shows the dispersal pattern of a juvenile buck that moves from Minnesota to Iowa in spring 2018, and then returns to his birth range in fall 2018. He was captured on March 18, 2018, approximately 6 miles north of Granger, Minnesota. As of Feb. 8, 2019, this animal (now a yearling approaching adulthood) is still on the air and transmitting locations within Minnesota. Click the play button on the map above to animate it.
Juvenile doe moves 75 miles
This map shows the dispersal pattern of a juvenile doe. She was captured on March 22, 2018, near Forestville/ Mystery Cave State Park. She began moving in early June 2018. As of July 23, she was located near Cannon Falls – a 75-mile trek from where she was captured. Click the play button on the map above to animate it.
- Deer 192
- Deer 143
- Deer 181
- Photo gallery
Deer in the study
Click on the photos below to view larger images of these collared deer. Photographs were provided by landowners in the southeast. If you are willing to share any high-quality pictures of collared deer, please send them to [email protected] .
- Hunting & collared deer
Ear-tagged and GPS collared deer are legal for harvest. We ask that you treat the marked animal like you would any other deer. If you would normally shoot the animal, then harvest it. If you normally wouldn’t shoot that animal, then don’t harvest it. By treating GPS collared or ear-tagged deer similar to any other deer, you will provide truthful representations of typical survival.
If you find or harvest a GPS collared or ear-tagged deer, please call 507-380-1858 and report the information. If there is no answer, please leave a message regarding the ear tags or collar number, how the animal died and your contact information. We will need to collect these GPS collars to download additional movement data for the study.
- Get involved
Most of the deer captures occurred on private land with permission from landowners. DNR staff will keep participating landowners updated on how specific collared deer use the local landscape. Broader findings from the study will be shared here as data becomes available.
The DNR is seeking landowners who would like to participate in future collaring efforts. Interested landowners or anyone who has harvested or encountered a dead deer with a collar can call 507-380-1858 or email [email protected].
Why is CWD a concern?
CWD is an infectious neurological disease that affects deer, elk moose, caribou and reindeer. It causes brain degeneration of infected animals and results in emaciation, abnormal behavior, loss of bodily functions and death. CWD is one of the greatest threats to the long-term health and size of Minnesota’s deer population. Studies of CWD-infected deer herds in Wyoming and Wisconsin have shown population declines and fewer mature bucks. There is no evidence that humans are susceptible to CWD, but new guidelines from the U.S. Centers for Disease Control and Prevention caution hunters not to eat deer that are known to be infected with CWD.
For more than a decade, the DNR has maintained aggressive surveillance efforts, resulting in more than 71,000 deer being tested for CWD.
The deer movement study is focused on the CWD management zone in a 30-mile buffer centered on Preston, Minnesota, and includes Fillmore, Houston, Olmsted, and Winona Counties. Southeastern Minnesota’s CWD management zone is being studied because 50 wild deer have tested positive for CWD in this area since 2016. Movement data will be used to help predict pathways of potential CWD spread and guide management efforts.