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Deer Vehicle Collisions
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Deer-vehicle collisions (DVCs) are one of the most visible negative impacts that deer populations have on society. As managing deer involves balancing the positive benefits of deer with their negative impacts, it makes sense to consider DVCs when making deer management decisions.
For additional Information….
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Deer-vehicle collisions (DVCs) are one of the most visible negative impacts that deer populations have on society. As managing deer involves balancing the positive benefits of deer with their negative impacts, it makes sense to consider DVCs when making deer management decisions.
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Collection and analysis methods
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The Wisconsin Department of Transportation (DOT) collects data on the number of vehicle crashes with deer that are reported by law enforcement agencies. Currently, data is available for each county on an annual basis.
The DOT has kept track of reported DVCs on a statewide basis since 1979, but only on a county basis since 1987. The DOT publishes an annual summary of DVC. Accidents must be reported to DOT if the reporting threshold ($1000+ property damage, and/or injury, and/or $200 damage to public property) is met. In 1996, the monetary threshold for property damage changed from $500 to $1000. Reports can either be written by law enforcement or citizens involved in the accident, however, only law enforcement reports are included in annual DVC counts.
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Principally, DVC data would be used to track changes in time of DVCs, which would indicate how this impact of deer on society is changing. CDACs will have to decide whether observed DVC levels are acceptable, and whether population objectives and antlerless quotas should be altered for the purpose of reducing DVCs. This assumes that DVC data is sound and is providing useful information.
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Limitations and precautions
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It’s important to realize that we never know exactly how many deer-vehicle collisions occur each year. DVC data is imperfect, so the number of DVCs in a report is not the true number of DVCs that actually occurred. However, imperfect data doesn’t necessarily mean bad or useless data. What it means is that we have to understand it and take care in interpreting what the data is telling us.
We have observed a general decline in ALL vehicle accidents and over time, not just DVCs. This could be for a whole host of reasons; safer cars, better roads, more law enforcement, etc… The bottom line is that these factors could also influence changes in DVCs in a way that has nothing to do with deer numbers.
Perhaps the most important thing we can do to ensure that data is useful is to collect it the same way every year and every place. If data collection is not consistent, then we cannot be sure if changes in the numbers of DVCs are real or caused by changes in data collection procedures. When wildlife biologists set up wildlife surveys, they place a lot of emphasis on collecting data in a consistent manner. DVC data is different from most data in that it hasn’t been collected for the purpose of monitoring deer populations and we have little to no control over how the data is collected. The bottom line: consistency in data collection is critical!
We’ve done some research to examine the usefulness of DVC data in Wisconsin. This involved interviewing about 35 sheriff departments in Wisconsin to determine their reporting procedures. The DVC data collected by the DOT comes strictly from law enforcement reports, so law enforcement policies and procedures have a big impact on reported DVC numbers. We found that sheriff’s departments varied substantially in their policies of responding to (and reporting) DVCs; from some departments always responding, to others only responding if the vehicle was disabled in the crash or someone was injured, and everything in between. Additionally, policies for responding to DVCs have changed over time as budgets and priorities change; e.g. some counties that used to respond regularly to DVCs no longer do. This variation in procedure makes comparison between counties or across years very difficult: are changes in DVC data due to changes in the true number of DVCs, or changes in reporting?
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Additional background materials related to this metric
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