PSU Deer Study

Duane’s COVID summer project centered around rats in the barn but it’s not hard to see the parallels to deer management. 


We kicked off this series explaining the relationship between deer densities and harvest. It is not a straight give and take no matter how much we want or expect it to be. Deer density and how it relates to the effort to see or harvest a deer is non-linear. That is, as deer densities decline it takes exponentially more effort per deer seen or harvested.

Our COVID summer project complete with protagonist, antagonist, and bard is a not just an allegory of deer management but almost a direct comparison when we look at familiar and recurrent beliefs that deer have been “wiped out” in <fill-in-the-blank>, Pennsylvania.

Pulling out all the stops, Phase IV of rat eradication included adding a kill trap to the mix called the A24. This trap is a humane killing trap that was developed in New Zealand where non-native mammals have decimated the native fauna. The only native mammals in New Zealand are bats and marine mammals, which means that none of the native bird, reptile, and invertebrate species have adaptations against mammalian predators – they don’t even recognize them as predators.

After being deployed for about a month, the A24 has not killed a single rat. How’s that for the Law of Diminishing Returns. Just this week we finally got video of a rat taking some seeds sprinkled underneath it. The repeating trap has even dried up with only one removal recently after weeks of zero rats partaking in the slide. Videos show there are still rats with clips showing 1-2 rats at a time – but mostly just a single rat.

Shanty vs Chateau

Clearly, there is no way to trap and shoot our way out of this problem. Eliminating rats also requires eliminating habitat. That’s right, hitting them “where they live” so to speak. The rat army marches on its stomach. Between raiding the cucumbers and tomatoes in the greenhouse and the feed scattered by chickens in their pen, there is no shortage of food. They aren’t just scraping by in a shanty town. 

Habitat is also a big part of the story about white-tailed deer.

Deer were nearly exterminated from Pennsylvania by 1900 through a combination of factors: 

  1. Unrestricted harvest for commercial sale 
  2. Subsistence hunting, and
  3. Loss of habitat when much of Pennsylvania was stripped of its forests.

You might enjoy reading a book by E. N. Woodcock (b. 1846, d. 1917), who hunted and trapped in Potter County, titled “Fifty Years a Hunter and Trapper”.  He relays his first-hand account of declining catch per unit effort although he didn’t know to call it that. 

“Like other boys who lead an outdoor life, I grew stronger each year and as I grew older and my trap lines grew longer and my hunts took me farther into the woods. Finally as game became scarcer my hunts grew from a few hours in length to weeks and months camping in a cabin built in the woods in a section where game was plenty.”

-E.N. Woodcock

If you want to eliminate deer, you need unrestricted hunting and habitat decimation. 

Photo of a former forest in Tioga County, Pennsylvania in the book “Pennsylvania Trees” by Joseph Simon Illick, Dept. of Forestry, June 1914, Harrisburg, PA; Wm. Stanley Ray, State Printer, 1914. In Pennsylvania during the late 1800s and early 1900s thousands of acres of forest were stripped of trees and abandoned, which then burned under destructive fires.

Today, deer are managed, primarily, by a single tool – recreational hunting. If Duane only applied a single tool to his rat problem, this would have been a short series and the graph would look very different. To move the needle on the local rat population, 4 different methods were implemented with 2 of them operating continuously. A no-holds-barred full-frontal approach – which would be equivalent to no regulatory restrictions on deer harvest. But like the rats, they still have that chateau to live in – habitat that conceals and provides.

The Show-Me State

For biologists, data speaks volumes. Experiments have been conducted with unrestricted hunting and deer reduction. An excellent one was conducted in 1971 in Wisconsin at the Sandhill Wildlife Area. For 28 days in a 14.3 square mile area with 86-160 hunters/day (6-11 hunters/mile2), a total of 593 deer were harvested. A population of ZERO was achieved, but towards the end it took 50 hunter-days per deer killed! You don’t need to be from Missouri to see that curve.

Total removal of deer on 14.3 sq. miles took 28 days, Sandhills Wildlife Area, Wisconsin. Data from: Creed, W. A. 2001. The total removal hunt. Pp. 53-66 in J.F. Kubisiak et al. Sandhill whitetails: providing new perspective for deer management. Wisconsin DNR.

The Impossible

While it may feel like there are no deer left in the woods on the few days you can get out there, it is not a reality. Total removal of deer cannot happen because the antlerless harvest is limited by an allocation of licenses. And that allocation goes mostly unfilled.

I had a queen-sized bed once where the most comfortable place was smack in the middle. Not too hard, not too soft – like Goldilocks it was just right.  Pennsylvania is the “just right” spot for deer in North America. Our winters are not too snowy, and our climate is cool enough that most deer diseases are not an issue (although that is changing). Plus, we get plenty of precipitation (another potential limiting factor).

If you look at the relationship between latitude and buck harvest density (antlered deer harvested per square mile), you can see that not only is Pennsylvania near that peak of that curve, but we’re almost an anomaly like several other states.

The possibility of Duane buying a lottery ticket is higher than that of eliminating deer in any area with our current system of management. 


While we had some fun hunting down this mischief of rats, this in no way equates to our feelings about deer. The white-tailed deer is native species cherished by millions of people – not to mention the biologists who manage them. We are hopeful that our comparison gave you a new perspective on the management of this wonderful species. 

We enjoyed it anyway 😊

-Duane Diefenbach and Jeannine Fleegle

Posts in this series:
Diminishing Returns
A man, A plan, A rat
Phase II: A repeating trap
Phase III: What every story needs

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