Chronic Wasting Disease Research at the USGS-Wisconsin Cooperative Wildlife Research Unit

 

Scraping behavior as a potential means of Chronic Wasting Disease (CWD) transmission

 

Michael Spelman

Wildlife Ecology 299 Final Project

 

What is a scrape?

 

A scrape is initiated by a male scent-marking a low hanging branch, followed by pawing a shallow depression into which they urinate.  It is used to establish dominance among males and to communicate with does (Miller and Marchinton 1999).  Additional behaviors at scrapes include sniffing or licking the overhead branch and sniffing the soil.

 

Why do we think scraping has the potential to spread CWD?

 

CWD infection is higher in male deer than in female deer (Miller and Conner 2005, Grear et al. 2006).  Currently the reason for higher disease prevalence is unknown, but hypotheses suggest that transmission among bucks may be a possible mechanism.


There is the potential for CWD to be transmitted via the environment (Miller et al. 2004).

Environmental transmission could be via saliva, urine, and feces (Bollinger et al. 2004), among other routes.

Scraping is an important aspect of deer social interaction, especially for males.  Scrape behavior involves activities that bring deer in contact with urine, saliva, and possibly contaminated soil.

 

Scrapes could be an important route of transmission that would account for the difference in prevalence among different sexes and ages.

  • Male deer interact more with scrapes than females (Alexy et al. 2001) and male deer have a higher prevalence (Grear et al. 2006).
  • More scrapes are made by mature male deer (Alexy et al. 2001) supported by higher prevalence among older deer (Grear et al. 2006)
  • Few cases involve young deer (Salman 2003), which will generally not be engaged in scraping behaviors.
  • There does not seem to be any difference in susceptibility based on sex or age (Grear et al. 2006)

 

Hypotheses under investigation

 

H1:  Multiple deer will interact with a scrape site in ways that might spread CWD.

 

 

Fig. 1. The first picture shows a buck urinating at a scrape.  The second picture shows a different buck interacting with the area where the first buck urinated.

 

 

H2:  Male deer will engage in more behaviors at scrapes that could potentially spread CWD than females.

 

 

Fig. 2. A picture of a buck and a doe visiting a scrape.

 

 

H3:  Adult males will engage in more behaviors that could potentially spread CWD than younger bucks.

 

 

Fig. 3. A picture of an adult buck and a yearling buck visiting a scrape.

 

 

Study area

 

The study area was located in the Sandhill Wildlife Demonstration Area (Babcock, WI, USA) which is owned and operated by the Wisconsin Department of Natural Resources.  It contains 9,150 fenced acres, and has been used to study deer ecology since 1962.  About half of the area is upland forest (aspen and oak) or grasslands, the rest is marsh (cattails and sedges), lowland brush (willow and bog birch), and developed areas (e.g. parking lot). 

 

Please note that CWD has not been found in deer within the Sandhill area.  This location was chosen because it provided and ideal setting for studying deer behavior.

 

More information about Sandhill can be found at:

http://www.dnr.state.wi.us/org/land/wildlife/reclands/sandhill/index.htm

 

Methods

 

  • Started looking for scrapes on 9/30/2005
  • Motion sensitive digital cameras installed near scrapes (at least 1 km apart)
  • Total of 11 Cameras
  • Pictures taken at 1-2 second intervals when triggered
  • Checked weekly to recover images
  • Moved Camera if no interactions
  • Cameras taken down on 11/20/2005 and 11/26/2005

 

Scrape Behaviors

 

All photographs taken by the cameras were reviewed for deer behavior at the scrape.  The behaviors we were interested in were:

 

1. Branch Lick: Involved licking or otherwise depositing saliva on the overhead branch

2. Mark Overhead Branch:  A combination of licking and/or sniffing along with antler rubbing

3. Pawing Ground: Pawing the soil under the overhead branch

4. Sniff Branch: Sniffing the overhead branch

5. Sniff Soil:  Sniffing the ground that had been scraped or its immediate vicinity

6. Urinate:  Urinating on the pawed ground or its immediate vicinity

 

(Click on the specific behavior to watch a video clip example)

 

Behaviors were also grouped based on whether they could potentially:

1.  Deposit CWD into the environment (urination)

2.  Expose a deer to CWD (sniff branch and sniff soil)

3.  Both deposit CWD and expose the deer (mark overhead branch and branch lick)

4.  Did not have the potential to deposit or expose the deer to CWD (paw ground)

 

Results and discussion

 

H1:  Multiple deer will interact with a scrape site in ways that might spread CWD

 

Deer were observed engaging in behaviors that have the potential to spread CWD (22 deposit interactions, 170 exposure interactions, and 88 that could potentially do both) and multiple deer were recorded interacting with same scrape.

 

Number of bucks interacting with different sites

 

Site

Male Fawns

Male Yearlings

Male Adults

Total

Site 1 - Stovepipe

0

0

2

2

Site 2 - North Road Mid NW

0

0

0

0

Site 3 - North Road – Mid NE

0

0

0

0

Site 4 - North Road - NE Gate

1

0

3

4

Site 5 - Island

0

2

5

7

Site 6 - NW-SW Border

0

1

3

4

Site 7 - North Bluff

0

1

6

7

Site 8 - SE Fence Line

0

2

3

5

Site 9 - G1 Flowage SE-SW

1

2

13

16

Site 10 - North Gravel Road

0

0

4

4

Site 11 - Swamp Buck Trail

0

0

0

0

 

Therefore, if environmental contamination via saliva or urination are found to be important means of transmission, then scraping behavior may be a potential mechanism for transmission of CWD

 

H2:  Male deer will engage in more behaviors at scrapes that could potentially spread CWD than females

 

We found that males visited scrapes more frequently and spent more time at scrapes than females.  There was also a difference in the frequency with which behaviors were performed by males and females (Fig. 4), with males engaging in all of the behaviors more often than females.  Thus CWD infected males would have a higher potential to deposit infectious prions into the environment, and susceptible males would have a higher potential to expose themselves to CWD.

Fig. 4.  Frequency of scrape behaviors for male, female, and “antlerless” (fawns that could not be identified by sex) deer.

 

 

There was also a difference in the relative frequency of behaviors performed by males and females and the proportion of time spent on different behaviors (Figs. 5 and 6).  Males were more likely to paw the ground or mark overhead branches, while females were more likely to sniff the soil.  Males were more likely to show scrape behaviors that could both potentially deposit and expose individuals to disease, thus providing the potential for transmission among males (which is consistent with CWD prevalence data).

Fig. 5.  Distribution of scrape behaviors by males

Fig 6.  Distribution of scrape behaviors by females

We also evaluated how the frequency of behaviors changed over the course of the breeding season (Fig. 7).  Males interacted with the scrapes more than females throughout the breeding season.

 

Fig. 7.  Frequency of male and female behavior at scrapes during the breeding season.

 

H3:  Adult males will engage in more behaviors that could potentially spread CWD than younger bucks

 

We found that adult males interacted more often with scrapes and spent more time visiting scrapes than younger bucks (Fig. 8).  Thus adult bucks are more likely to both potentially expose themselves to CWD and potentially deposit the prion into the environment.

 

Fig. 8.  Frequency of adult buck, yearling buck, and buck fawn behaviors at scrapes.

 

 

Although adults interacted with scrapes more often than younger bucks, the relative frequency and proportion of time spent on different behaviors was the same for all age classes (Figs. 9 and 10).

 

Fig. 9.  Distribution of scrape behaviors by adult bucks

Fig. 10.  Distribution of scrape behaviors by yearling bucks

(Note: while the percentages may not be exactly the same for yearlings and adults, there is not a statistically significant difference in the distribution of behaviors)

 

We also evaluated the frequency of behaviors among different ages of bucks during the breeding season.  Adult males interacted with the scrapes more than yearlings and fawns throughout the breeding season (Fig. 11).

 

Fig. 11.  Frequency of scrape behaviors by adult, yearling, and fawn bucks during the breeding season.

 

We also found that older deer interact more frequently with a scrape when it is first initiated, but as time goes on, the average age of the deer using the scrape declines (Fig. 12).  This implies that if CWD transmission occurs at scrapes then adult bucks (who have the highest prevalence of CWD) are interacting with the scrape first, followed by younger bucks (who are more likely to be susceptible).  This could facilitate transmission between age classes.

Fig. 12.  Average number of antler points per buck during the breeding season for Sites 6, 7, and 9b using number of antler points as a measure of age.

 

 

Important conclusions

 

This study was not designed to show that scraping behavior spreads CWD.  However, the behavior of deer at scrapes is consistent with prevalence of CWD reported in white-tailed deer, especially in bucks. 

 

More research is needed on environmental transmission of CWD, especially via urine and saliva.  This will allow scientists to evaluate transmission via scraping.

 

If scraping is shown to spread CWD, the research in this study can be used to help control the transmission of the disease.  For example, additional harvest before scraping begins (late September/early October) could target adult bucks.  This will help remove infected individuals and reduce the contamination of scrapes with CWD.

 

Literature cited

 

Alexy, K. J., J. W. Gassett, D. A. Osborn, and K. V. Miller.  2001.  Remote monitoring of scraping behaviors of a wild population of white-tailed deer.  Wildlife Society Bulletin 29(3):873-878.

 

Bollinger, T., P. Caley, E. Merrill, F. Messier, M.W. Miller, M. D. Samuel, and E. Vanopdenbosch.  2004.  Chronic wasting disease in Canadian wildlife: an expert opinion on the epidemiology and risks to wild deer.  Canadian Cooperative Wildlife Health Centre, Saskatoon, SK 32 pp.

 

Grear, D. A., M. D. Samuel, J. A. Langenberg, and D. Keane.  2006.  Demographic patterns and harvest vulnerability of chronic wasting disease infected white-tailed deer in Wisconsin.  Journal of Wildlife Management.  In press.

 

Miller, K. V. and R. L. Marchinton.  1999.  Temporal distribution of rubbing and scraping by a high-density white-tailed deer, Odocoileus virginianus, population in Georgia.  The Canadian Field-Naturalist 113:519-521.

 

Miller, M.W., E. S. Williams, N. T. Hobbs, and L. L. Wolfe. 2004.  Environmental sources of prion transmission in mule deer.  Emerging Infectious Diseases 10(6):1003-1006.

 

Miller, M. W., and M. M. Conner.  2005. Epidemiology of chronic wasting disease in free-ranging mule deer: spatial, temporal, and demographic influences on observed prevalence.  Journal of Wildlife Diseases 41:275-290.

 

Salman, M. D.  2003.  Chronic wasting disease in deer and elk:  scientific facts and findings.  Journal of Veterinary Medical Science 65(7):761-768.

 

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