In the Field: How DNR Estimates Deer Harvest

by Anna Mitterling, Wildlife Cooperative Coordinator, MUCC

Deer season has come and gone, and you have been reaching out to your neighbors to get the final deer kill for the seasons. You were able to get harvest data from most of the cooperative members, and by talking with neighbors have some good guesses on what hunters who are not part of the cooperative were harvesting. Despite only having 7,000 or so acres to account for, you were unable to account for all of the deer harvested in the cooperative area. Regardless, between the harvest information you have, and the observation and harvest data you and your neighbors have collected over the last several years, you are very confident to set harvest goals for the cooperative when the following fall arrives. For some reason, many hunters do not accept that the state is capable of making good harvest quotas, yet believe it or not, they have a pretty accurate understanding on what is going on at statewide and regional levels. Take confidence in understanding your part of the woods, and trust that maybe DNR has a better idea of statewide and regional data than we may think.

I had a nice phone conversation with our very own Deer, Elk and Moose Management Specialist, Chad Stewart. He has had the benefit of working both in Michigan as well as Indiana, where they have mandatory check, and no survey system. He was kind enough to help me break down the benefits and challenges of the different ways of making harvest estimates – yes they both estimates either way. Neither state has a concrete, definitive number of how many deer were harvested in a given year.

Michigan

In 2014, DNR estimated that the total number of deer harvested was 322,367, +/- 2% (Frawley, 2014 Deer Harvest Survey). While we would like a specific number, it is not realistic to think that we could accurately say that 329,152 deer were definitively shot in all of Michigan in 2014. But based on some of the rationale I will explain below, DNR is 95% confident that Michigan hunters harvested right around 322,367 deer in 2014.

DNR is responsible for setting regulations for an entire state. They have the expertise and resources to make calculated estimates based on decades of solid data from hunter surveys and check stations. Michigan is one of, if not the only, state who has a dedicated statistician to run through the hunter data and calculate usable numbers to guide regulations. Michigan has the best biological data collection of any state, and reached over 1 million individual deer checked since the late 80s – and all that without having mandatory deer check.

When DNR outlines their data, they understand the following:

1.     The data is an estimate that is comparable year to year
2.     The required number of people were surveyed to reach the statistical confidence needed to draw conclusion

Chad explained things in another way. Say we flip a coin ten times. We know that the chances of getting heads is 50%, but just ten flips may not show that. The more sets of ten coin flips we do, the closer we get to the 50% – to a point. But there also reaches a point where it doesn’t matter if we flip the coin 1,000 times or a million, either way, we will be very close to 50%. The same logic comes to the amount of data on deer harvest we need to collect to accurately illustrate the statewide harvest numbers. Knowing that point, is where the complexities of statistics come in, but be rest assured that they are reliable.

More states are heading in the direction of using estimates to manage deer herds based on trends year to year, but like Michigan, also taking other factors such as deer damage, and road kill into account as well. No, Michigan does not know an EXACT number, but they are confident in a LIKELY number, and more importantly, how the deer population is trending. Which is really all a state level manager needs to know.

Indiana

Indiana has mandatory deer check, yet there is not a guarantee that every single deer kill is reported. Given that, they don’t actually know how many final deer were harvested, but they do know the minimum number of deer killed. They have pretty consistent reporting every year, and are able to provide good comparative estimates year to year. They also collect biologic data at deer check each year, and collect information on 125-130,000 deer, again also consistent year to year.

When Indiana DNR compiles their data, they understand the following:

1.     They know the minimum number of deer harvested
2.     The final harvest number assumes that reporting rates are constant year to year

One of the challenges with this reporting system is that assumes consistency between previous years. When one variable is changed that could affect reporting, the reported harvests lose value.  For instance, Indiana recently developed an online check system after years of having deer check stations.  Did this make it easier for hunters to report deer and increase compliance?  Did it make it too easy, so hunters decided to stop reporting deer?  Or maybe it didn’t change anything, with the assumption that honest hunters will register their deer and dishonest ones won’t register their deer.  The point is that the effect of this change is unknown, and the numbers reported for deer with this system may not be done the same as before this system was in place.  It’s only once a season is maintained for several years without interruption that the state can again develop a consistent trend and truly understand the direction the deer herd is moving.

A benefit of the mandatory check is that the results are available more quickly for evaluation and regulation recommendations. Also, they are able to identify  harvest intensity over the seasons, knowing the number of deer harvests within a specific season, rather than for the season as a whole.

In Conclusion

This may be a harsh reality to face, but given the information DNR has to evaluate and compare, consider that possibly they have a better grasp of deer trends at the statewide/regional level than we do of harvests in our neighborhood. We make assumptions about our neighbors, we are not able to talk to all of them, nor do we have confidence that our neighbors are truthful about their harvests. The hard reality is that we may be quick to jump on DNR because we feel they don’t have the best data, but what are we doing to make sure we have the best data before we take on the management of the deer in our backyard? Are you 95% confident you know the accuracy of the number of deer harvested within your township?

On the flip side, the data DNR has shows its greatest value when comparing data across 5-10 years and at a regional or statewide level. They can’t infer population changes smaller than the Deer Management Unit, but cooperatives should have a good understanding how their local deer herd fluctuates year to year. A cooperative is able to gather data to accurately estimate harvest and even populations with adequate accuracy given the scope of the impact, or at that local level.

The awesome thing of a cooperative is that it has the possibility of creating an environment where you can work with your neighbors to pool data, both observations and harvest, to then draw solid conclusions of harvest goals and obtainable harvest standards. DNR’s job is to simply make sure they are able to provide the tools you need to manage deer in your area, as well as make sure that we are not at a risk of damaging the sustainability of the resources we all love and value.