Casey M. Wilke, Josh Kamrowski, Kyle Marinoff, and Christopher J. Yahnke, The Effect of Baiting on the Social Behavior of White-tailed Deer in Central Wisconsin
Abstract
Chronic wasting disease (CWD) in white-tailed deer has been a growing concern in the US western and mid-western states since 1960. In 2001, Wisconsin�s overly abundant deer herds became subject to CWD. How CWD is transferred from one individual to another remains a mystery, but it is possible that baiting deer increases the probability for CWD transmission. We investigated how deer alter their behavior at bait sites, and tested the null hypothesis that there is no change in deer behavior at different types of bait stations. We also considered how this behavior may contribute to the transmission of CWD.
Camera and direct observations were taken at 2-gallon and 10-gallon whole kernel corn bait stations. A control site was monitored with human observations only. The 2-gallon and 10-gallon sites were baited in alternating bait piles and bait broadcasts.
Direct observation results showed that significantly more deer visited the 10-gallon site (χ2 = 14.6>5.99, p<0.05). Camera observation results showed that there were significantly more deer less than two meters apart at the bait piles than at bait broadcasts (χ2 =7.61>3.84, p<0.05). Camera observations also showed that deer activity peaks at different times of the day at the 2-gallon and 10-gallon bait sites.
The significant results lead to rejection of the null hypothesis that there is no change in deer behavior at different types of bait stations.
Introduction
Chronic wasting disease (CWD) has been a growing concern in Wisconsin since it was first discovered in wild white-tailed deer in 2001 (Williams, et al., 2002). CWD was first discovered in a group of captive mule deer in Colorado around 1960. Some progress towards understanding the disease was made in 1978 when it was identified as a transmissible spongiform encephalopathy (TSE) (Williams, et al., 2002). An animal with a TSE disease will develop lesions on the brain caused by an agent called a prion (Salman, 2003). Once CWD was identified to be a TSE, hypotheses about its origin began to be developed. Researchers hypothesize that it could be an irregular form of TSE, a new strain of scrapie (the TSE that develops in sheep), that it surfaced from an unknown prion strain that already existed, or that it is caused by a spontaneous transformation of a prion protein (Salman, 2003).
A prion is a natural protein that occurs in all animals, but it has two forms. The normal form is found in the brain where it is believed to incorporate copper into the brain. This form is considered to be folded correctly. The form that is responsible for TSE disease is a prion folded incorrectly. The deformed prion readily converts normal proteins into abnormal proteins, causing disease. Prions do not contain DNA or RNA, and are difficult to destroy. Other pathogens contain DNA or RNA, and can be destroyed by submersion in formaldehyde, boiling in water, or exposure to excessive heat (Yam, 2003). Prions can only be destroyed with sodium hydroxide or sodium hypochloride (Williams et al., 2002).
Transmission of CWD is not well understood. Factors to consider include lateral transmission (passed from individual to individual) and indirect transmission (passed to an individual from environmental contamination). CWD has been found in the lymph tissue of the alimentary tract; therefore, transmission through feces and saliva is likely (Salman, 2003).
A study performed with white-tailed deer infected with bovine tuberculosis (TB), a bovine TSE, showed that TB transmission increased when the deer were baited. Baiting increases the chance of individuals coming into direct contact with one another. Population densities around the bait sites increase (Miller et al., 2003), which increases droppings and contaminates soil. Also, the bait can be contaminated with saliva and nasal emissions from the deer (Miller et al., 2003).
At the present time, baiting creates a huge debate. The Wisconsin Department of Natural Resources (WDNR) states that baiting would increase CWD transmission through deer herds and should be banned (Lawmaker Proposes Limits to Baiting Deer, 2003). Businesses argue that transmission of CWD is still poorly understood, and a ban on baiting would drastically hurt sales of feed corn (Walters, 2003). Hunting, viewing, and other social aspects concerning deer bring in $1 billion per year for Wisconsin (Joly et al., 2003). Banning baiting could decrease interest in deer recreational activities, and affect Wisconsin�s economy. Hunters are also against the ban because they argue baiting increases the likelihood of spotting and shooting deer. However, hunting success rates with and without bait vary only by a small amount (Toso, 2001).
We studied behavior of deer at different bait sites to observe if white-tailed deer altered their behavior at bait sites in such a way that could contribute to the spread of CWD. We tested the null hypothesis that deer do not alter their behavior at different bait stations.
Methods
The study area was a portion of the Sternberg Forest, an 80-acre plot of land in Mosinee in Marathon County. Three different feeding sites were established in the study area. The control site consisted of natural forage; no manipulation was done to this site. The 2-gallon site had a rotation of two gallons of whole kernel corn in a pile for two weeks followed by 2 gallons of corn broadcast for two weeks. The 10-gallon site had ten gallons of whole kernel corn in the same rotation of pile versus broadcast as the 2-gallon site. The bait for these sites was refreshed every Monday, Wednesday, and Friday for the duration of the study.
Direct observations took place at each site. These observations ran from January 26 to March 12, 2004. Each observer sat in a natural blind and wore a camouflage suit to remain concealed at the sites. Observations took place from 2:30PM to 6:30PM on the designated observation days for each observer. Direct observations ran in a rotation of one week on and one week off with continual baiting. Data recorded included: name of observer, date, start and end time of observations, weather conditions, site, time of deer seen, number of deer seen, age of deer (adult or fawn), contact within two meters between deer, and any comments on activity. Because transmission of CWD to deer may involve other animal carriers (such as squirrels, chipmunks, mice, and birds), we also noted what other animals utilized the bait sites.
Camera observations took place at the 2-gallon and 10-gallon sites only. The cameras were set up three meters away from the bait pile. These observations ran from February 18 to April 7, 2004. The cameras were on 24 hours a day. Each camera was set to take images every minute and record events (date and time of activity) every 30 seconds only when motion was sensed. A ten-second video was recorded after each image. Data recorded from images included: number of deer, type of contact or distance less than two meters between deer, age of deer (adult or fawn), and date and time deer were present.
Chi-square analysis was conducted on the number of pair-wise deer contacts less than two meters at piled versus broadcast bait sites and the total number of deer at control, 2-gallon, and 10-gallon sites.
Results
From the direct observation data (Figure 1), one deer was observed at the control site, nine deer were observed at the 10-gallon site, and no deer were observed at the 2-gallon site. A total number of ten deer were observed for the entire season. There were significantly more deer at the 10-gallon site (χ2=14.6>5.99, p<0.05).
Figure 1. Number of deer observed at bait stations based on human observations. The expected values are derived from the null hypothesis that there is no difference in the number of deer among bait sites.
Images collected from the camera at the 2-gallon site show that the greatest number of deer visit the site at 0900 (Figure 2). The data also shows that deer frequent the site at 1800 and were active at lower levels throughout the day. At 0900, 48 deer were seen in images for the entire study season, and 21 deer were seen in images at 1800. The camera at the 10-gallon site malfunctioned and no images were collected that could be compared with the 2-gallon site.
Figure 2. Total number of deer in images taken by the digital camera at the 2-gallon bait site.
Event data from the digital cameras showed that most activity at the 2-gallon site occurs at 0900 and 1800 (Figure 3). Although no images are collected from event data, the pattern is similar to the image data suggesting the events recorded represent deer activity.
Figure 3. Total events recorded by the digital camera at the 2-gallon bait site.
Although image data collected by the camera at the 10-gallon site was not usable because of a software malfunction in the camera, a usable events log was generated by the camera. The event data for the 10-gallon site shows that activity doubles at 0600 and 0700 than at any other time of the day (Figure 4). There were 56 events recorded at 0600 and 54 events at 0700.
Figure 4. Total events recorded by the digital camera at the 10-gallon bait site.
The number of deer interactions less than two meters distance was greater at the bait piles rather than at the broadcast treatment for the 2-gallon site (χ2 = 7.61>3.84, p<0.05). Twenty-eight deer were within two meters of one another at the pile treatment, and only 10 deer were within two meters of one another at the broadcast treatment.
Figure 5. Number of deer interactions within 2 meters at the 2-gallon bait site for piled versus broadcast bait. The expected values are derived from the null hypothesis that there is no difference between the two treatments.
Discussion
The chi-square values for the direct observations and the pile versus broadcast of the 2-gallon site both are greater than their respective critical values (14.6>5.99 and 7.61>3.84). This indicates that the null hypothesis of no difference among treatments can be rejected.
Our limited data suggests that deer do alter their behavior at different types of bait stations. Deer are in closer contact with one another at piles than at broadcast bait sites. According to the direct observations, more deer are present at the baited sites than at the control site. There is also a difference in the pattern of activity between the 2-gallon and 10-gallon sites.
The camera at the 10-gallon site did not take clear images, which made it difficult to count the number of deer at the site. However, the event data from this site likely represents deer activity. The 2-gallon event data (Figure 3) strongly resembles the 2-gallon image data (Figure 2), where most activity and highest number of deer are evident at 0900 and 1800. Because the 2-gallon image and event data are closely related, we are confident that the 10-gallon image and event data would also be closely related.
This study focuses on a small number of deer in a limited area, but nevertheless yielded useful results. It also illustrated the difference between direct versus remote observation techniques. For future study seasons, direct observations may not be performed at all. The cameras capture more and higher quality data than what each observer could capture in their designated hours.
The cameras also take video clips that enhance the image data. The image below shows four deer, but does not show the type of interactions that are taking place. However, the video clip that follows the image shows that there is aggression exhibited over the bait.
Figure 6. Image with video clip. The image shows four deer at the 2-gallon bait site; the video clip shows the behavior that the deer express at the bait site. Click on image to view video.
From this image, a person collecting image data would only count one deer, but after watching the video, it would be clear that there are actually two deer present in the image.
Figure 7. Image with video clip. The image shows just one deer at the 2-gallon bait site; the video clip reveals that there are actually two deer at the site at that time. Click on image to view video.
Camera observation strategies may vary for future data collection. The cameras may be placed at bait sites only and data among those sites can be analyzed. Cameras may not be placed at control sites because control sites often cover a broad area and the cameras need a narrow area to focus on. Or, if a control site is found where natural forage is concentrated in a particular area, a camera can be set up focusing on the concentrated natural forage.
Also in a future reference, the cameras can be moved to different study sites within the same study season. This will allow data from different deer to be collected rather than data from the same deer visiting the sites.
Acknowledgements
Great appreciation goes to Sue Kissinger for taking time to help us establish the study sites in the Sternberg Forest, to the UPDC and UEI research grants for providing the funds for the cameras and travel reimbursement, and to the field crew: Aimee Wiese, Rachel Marlett, and Tony Tuschen.
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