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Deer feed site behavior
White-tailed deer behavior at three feed settings in southern Michigan: Implications for transmission of chronic wasting disease (CWD)
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Summary
- Chronic wasting disease (CWD) is a fatal disease found in deer and it has been confirmed in Michigan.
- Common transmission routes for CWD include direct (deer to deer) contacts and environmental contacts (deer to contaminated soil).
- During winter, we investigated direct and environmental contacts of deer and accumulation of deer feces in southern Michigan at three feed settings: baited sites, food plots and agricultural fields.
- Direct and environmental contacts by deer were more frequent at bait sites compared to food plots and agricultural fields.
- Feces was more common at bait sites compared to food plots and agricultural fields.
- In agricultural areas with concern for CWD transmission, food plots and crop residue offer less risky food sources for deer.
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Background
Chronic wasting disease is a neurodegenerative pathogen that is contagious and once contracted is always fatal to deer. Approximately 250 deer have been confirmed infected with CWD in Michigan. Infected deer shed prions in mucous, blood, saliva, feces, and urine. Prions are transmitted through direct physical contacts among deer or indirect contact of deer with elements of their environment, including contaminated food sources. Also, as prions are shed in feces they can accumulate in soil.
Multiple studies have demonstrated that bait congregates deer and these results imply potential for increased transmission of infectious prions leading to increased transmission of CWD. Others contend that concentrations of deer also occur at food plots planted to attract wildlife and in agricultural fields, particularly in fall and winter. Ultimately, differences in potential for transmission of CWD among these three settings is related to deer interactions and accumulation of bodily fluids and feces.
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Approach
To evaluate potential differences in direct physical contacts among deer and contacts with the environment, we conducted observations of deer after hunting season (January – April) in southern Michigan. Deer naturally congregate at this time and we expected behaviors of deer to be less influenced by human interactions outside of hunting season. We used remote cameras to collect videos of deer at food plots and bait sites. To observe deer in natural habitat (i.e., agricultural fields), we drove randomly selected road transects. Observations of deer were limited to early morning and late evening because this is the time when deer are most active and observable.
To assess bioaccumulation of feces, we established 7-one-meter square sampling plots at all bait sites and food plots. We also established 7-one-meter square sampling plots along a 20 meter transect at locations where we observed deer when conducting road-based observations. When sites were free of snow, we collected feces from all sample plots at each site weekly. We later dried and weighed all fecal pellets collected from each plot.
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Findings
We sampled approximately 10 food plots and bait sites annually from 2021–2023. We compiled 630 observations of known sex-age deer during road-based surveys and conducted 3,542 observations of deer from videos (bait sites = 2,868, food plots = 674). For all deer observed, we detected significantly fewer direct contacts at food plots and transects compared to bait sites (Figure 1). We also observed significantly fewer environmental contacts at food plots and transects compared to bait sites (Figure 1).
Figure 1. Average number of daily direct, environmental, and self-contacts among deer observed at bait sites, food plots, and transects during winter (January through April) in south-central Michigan, 2021–2023. Light grey circles represent data points, and error bars represent 95% confidence intervals. Number of contacts (y-axis) was calculated from 16 potential 30-second video segments per site for daily observation periods (8 morning and 8 evening).
We detected 139 instances of fecal deposition at 26 baits sites, 126 detections at 23 food plots, and 74 detections at 18 natural congregation sites. The probability of finding a deer fecal pellet at bait sites was significantly greater than at food plots and natural congregation sites. Fecal material was found during 78% of the sampling events at bait sites, 43% of events at food plots, and 46% of events at natural sites. Average fecal deposition rates were highly variable (i.e., high SD relative to mean) regardless of site type and although not significantly different, we recorded an average of 1.04 g of deer feces deposited per day at bait sites, 0.22 g at food plots, and 0.33 g at natural congregation sites.
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Conclusions
At the three feed settings we examined during winter, direct physical contacts among deer were rare; but our findings indicate a greater likelihood of a direct contact at bait sites, potentially increasing the transmission of infectious prions. Also, environmental contacts occurred significantly more frequently at bait sites and one of the most frequent environmental contacts observed was a common feeding behavior involving deer pawing the ground and then contacting the ground with their nose and mouth. The combined effects of increasing probability to find deer feces and increased environmental contacts at bait sites increases the potential for transmission of prions in this feed setting. In agricultural areas with concern for CWD transmission, food plots and crop residue offer less risky food sources for deer.
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Research partners
- MDNR
- Applied Forest and Wildlife Ecology Laboratory at Michigan State University
- Safari Club International-Michigan Involvement Committee
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