Penn State Deer-Forest Study

We have written blog posts about how the most important component of a deer population is adult females. Their survival primarily determines whether a deer population increases or decreases. But as usual, they get snubbed. When it comes to survival or mortality, fawns still get all the attention – I guess because they mostly die from 4-legged predators instead of 2-legged predators.

Also, we have written how fawn survival in Pennsylvania is not a concern because

our fawn survival rates are above-average, and
any changes in fawn survival can be countered with changes in antlerless harvest.

In an analysis of fawn survival studies across North America, survival increases as amount of agricultural land on the landscape increases. However, Pennsylvania’s survival rates are above-average (above the regression line) given the amount of agriculture present.

Interestingly, a recent study came to the same conclusion in Louisiana. Researchers monitored fawn survival and adult female survival to investigate population growth and harvest potential.

The predator suite on the 120-mi² study area included bobcats, coyotes, and a restored population of Louisiana black bear (Ursus americanus luteolus, a subspecies of the American black bear).

Fawn survival rates on their study were only 27% – which is about half of what they are in Pennsylvania (~60%).

Survival rates for yearling females was 85.7% and for adult females 81.5% – similar to Pennsylvania.

Are these fawn survival rates worrisome for our southern counterparts? Nope. Basically, it’s what we’ve been saying all along – with fawn survival as low as 25% and adult female survival about 80% or greater, a deer population will be stable or increasing.

In fact, in this Louisiana study, researchers estimated that with the current survival and harvest rates the population was increasing at a rate of 6% per year! To stabilize it, they estimated yearling and adult female harvest rates would have to increase to be just under 20%.

If the antlerless harvest were completely eliminated, the population would grow by 15% per year. Under that scenario, the population would double in 5 years.

More evidence showing that throughout most of the range of the white-tailed deer, populations can be managed by adjusting the antlerless harvest – regardless of fawn survival rates.

-Duane Diefenbach

17 comments on “It Bears Repeating”

Very interesting. Thank you Duane.

Have you written any articles on mature buck movements in late season? I was trying to find something on that subject but unsuccessful. I’m curious as to what their movements/patterns are like this time of year, post rifle season and where they seek out food/cover?

Duane Diefenbach says:

December 17, 2020 at 8:51 am

I don’t believe we have written about late season movements, because it’s pretty boring. Little breeding occurs by mid-December and deer movements decline accordingly. All deer have returned to their core home ranges.

Thanks Duane,
This clears up some of the concerns about the various predators and their effect on the deer population. I still do think the Game Commission has substantially increased antlerless tags to deal with CWD.

Craig Cheselske says:

December 16, 2020 at 1:27 pm

We’re {hardcore old-timers} going so far as to wonder if CWD has been around forever. There are so many unknowns, how can we have trust in any of these numbers?
- Duane Diefenbach says:
  
  December 17, 2020 at 8:47 am
  
  CWD was discovered in CO and WY in the 1960s, but it has not been present east of the Mississippi until it showed up in Wisconsin, and now occurs in VA, MD, PA, and WV.
Duane Diefenbach says:

December 17, 2020 at 8:49 am

The only tool available to wildlife managers to slow the spread of the disease is to reduce deer densities. I addressed that issue in the blog post https://www.deer.psu.edu/who-knows-best/

Do the CWD prions that are in infected deer spread to the predators that eat them?

Duane Diefenbach says:

December 17, 2020 at 8:43 am

CWD is known to only infect cervids (white-tailed deer, elk, mule deer, moose, reindeer) so predators or scavengers will not get infected from eating a CWD-infected deer.

Correction 12/22/2020: I should have stated that there is no evidence that predators or scavengers can become infected. Just like there is no evidence that humans can contract CWD, but still it is not recommended to eat venison from animals diagnosed as CWD-infected.
- Woody Meristem says:
  
  December 21, 2020 at 7:44 pm
  
  Duane,
  You probably shouldn’t be so definite as to say “predators or scavengers will not get infected from eating a CWD-infected deer”. It would be fine to say that there’s no definitive proof that CWD can be acquired by predators or scavengers, but to say they “will not” is a bit too dogmatic given this paper — “Chronic Wasting Disease in Cervids: Implications for Prion Transmission to Humans and Other Animal Species” which can be read here — https://mbio.asm.org/content/mbio/10/4/e01091-19.full.pdf
- Duane Diefenbach says:
  
  December 22, 2020 at 8:33 am
  
  Yes, you are correct. Thank you for pointing that out. I have added a correction to my response.
  
  Also, you cannot say that a deer is NOT infected with CWD. All we can say is that CWD was not detected. A subtle but important difference. A deer could be infected but if the level of infection is too low the test cannot detect the disease.

This certainly makes good sense. Want more fawns? Keep the fawn-makers alive another year so they can produce more fawns. Want fewer fawns? Kill off the fawn-makers.

Without questing the deer populations are regulated by adjusting the anterless harvest. Therefore I think you would agree that the PGC is either purposely keeping the deer populations way below habitat carrying capacity; ignoring scientific facts; or mismanaging the deer herd as the doe license allocation has not nearly declined as has the deer population in some units/counties.
EXAMPLE: take McKean or Potter counties. Historically 40 years ago there were probably 40+ deer p/sq mile, definately too high. Not that many bear or coyote sightings back then as well. What was the doe allocation then? Of course the consistent number of annual doe license allocations during the 40 years hasn’t changed much, resulting in TODAY, deer populations maybe 6-7 p/sq mile. Carrying capacity with natural available foods in these “big woods” can sustain twice that amount of deer. I’ve had seasoned hunters tell me that they have spend consecutive days rifle hunting in these areas that they have hunted for years and can go 2-3 days without seeing a deer. But they will see bears and coyotes. But has the doe allocations reflected any indication to increase the deer herd? NO. WHY NOT?

Duane Diefenbach says:

December 17, 2020 at 8:41 am

Dan, there’s a lot to unpack in your comment but let me just share some facts. Deer densities on our study areas in Potter County are about 20 deer per square mile even with them enrolled in DMAP – one of our graduate students just completed her thesis on this topic. Deer densities statewide were reduced in the early 2000s but once those densities were reduced you can then reduce the allocation to stabilize the population. Hence, current antlerless allocations may not seem that different from pre-2000s. Finally, the PGC is one of the few (and maybe the only) that uses habitat metrics when making deer management recommendations. It’s all available in their Deer Management Plan https://www.pgc.pa.gov/Wildlife/WildlifeSpecies/White-tailedDeer/Documents/2009-2018%20PGC%20DEER%20MGMT%20PLAN%20-%20FINAL%20VERSION.pdf and annual reports https://www.pgc.pa.gov/Wildlife/WildlifeSpecies/White-tailedDeer/Documents/Antlerless%20Allocations%20and%20Supporting%20Information.pdf
- Rand Smith says:
  
  December 17, 2020 at 4:07 pm
  
  Start a deer study in Sproul State Forest! My hunch would be you get nowhere near 20 deer/ sq mi. Why is it the bear research area is in the Sproul but the fawn mortality studies were done elsewhere??
- Duane Diefenbach says:
  
  December 18, 2020 at 1:34 pm
  
  The first fawn survival study was centered on the Quehanna Wild Area, not far from the Sproul. Fawn survival was essentially the same as on the Susquehannock. We have done female survival studies on the Sproul.

Deer populations in Potter and Tioga Counties have been increasing steadily for the past 5 years and currently higher than I’ve seen in at least 15 yrs. I live here and am a Professional Wildlife/Habitat manager on private lands throughout NC PA. I have properties in 3A and 2G where 20 to 50 acres of food plots (Corn, Soybeans, Buckwheat, Brassicas, Cereal Grains) are eaten to the ground before Firearms Deer Season. Even when travelling through the “Big Woods” I see lots of deer. Habitat will be degraded again if this growth is not slowed again soon.

When can we expect to see gps movements of deer in rothrock? I have several trailcam pics of collared and tagged deer. My cams are up all year long.

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