Penn State Deer-Forest Study

Most of the time Mother Nature has a back up plan. And if we (people) don’t get involved or mess things up, her plan is fool proof.

There was yet another fawn survival study conducted. This time in Michigan. The spin this time was looking at how landscape and physiological characteristics (weight) influenced a fawn’s risk of mortality. Hypotheses included fawns occurring in areas of greater human development would have decreased predation risk but increased anthropogenic mortality risk; fawns in more forested areas would have greater overall mortality risk; and smaller fawns would have greater mortality risk from non-predation natural causes and, to a lesser extent, from predation.

Can humans save the day by protecting helpless fawns from vicious attacks by coyotes, bears, bobcats, and wolves?

The short answer is yes. But then we just run over them instead.

Let’s start broadly. Fawn survival in this study was 47% which is ridiculously similar to the heaps of other fawn survival studies conducted in North America. Predation was the leading cause of mortality followed by non-predation natural mortality and vehicle collision. No surprise there.

But looking at fawn mortality through the lens of land cover and body mass found that it influenced vulnerability to specific mortality risks, but the result was similar survivorship. E.g., human development reduced fawn predation, but that reduction was compensated by vehicle collisions. So fawns in forested habitats did not have a greater overall mortality risk.

Weight on the other hand did influence mortality risk by increasing non-predator natural mortality regardless of land cover. If you are a tiny bean, the odds are against you no matter where you live.

It’s tough being a deer mom. If you stay in the woods, your baby might be a snack. If you move to the burbs, your baby might be a road pizza. What’s a mom to do?

Doe walking away from camera with 2 fawns following behind her in the forest

Have 2!

Coyotes, bears, bobcats, wolves, Buicks, or none of the above – Mother Nature’s answer to this problem is to have a spare. While it continues to make people feel uncomfortable to see or know fawns die, there is nothing to worry about. Deer have it under control.

-Jeannine Fleegle
Wildlife Biologist
PA Game Commission

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14 comments on “…and a Spare”

Jeannine, your educated and entertaining writing is always a great start to the day!

I recently saw a very interesting PBS program on urban/suburban wildlife. The gist of it was how wildlife learn to survive in close proximity to humans. There was a segment on deer that dealt with adult does teaching their fawns how to cross roads safely. I guess some fawns just don’t pay attention in class. Thanks for another interesting article.

Any data on the relative survival rates for:
1. Single fawns
2. One of a pair of fawns
3. Both of a pair of fawns
I presume that the 47% survival rate quoted is a summation of survival for all of the above options.
Art Davis

Duane Diefenbach says:

February 14, 2023 at 5:17 pm

To date there is no evidence that the fates of twins are linked – they are neither more or less likely to survive. However, my guess would be that single fawns are less likely to survive because it is more likely to be the first-born of the mother (who is less experienced and likely lower body weight). Nearly all survival studies treat each fawn as independent in the statistical analysis – the one study that questioned whether this was reasonable assumption found that it was.

This is fascinating and educational. Thanks.

So the article stated, “fawns in more forested areas would have greater overall mortality risk”. Is this due to the landscape of the area (lack of places to hide) or that there are more predators in rural forested areas?

Thanks for your great insights!

Ron says:

February 14, 2023 at 11:44 am

Read the study. Section 4 “Discussion” gives information.

Great write up on the topic. The only question I would have is if the hunting harvest was included in the study. If it was included which area had the higher harvest rate for fawns.

Duane Diefenbach says:

February 14, 2023 at 5:12 pm

Good question! This study covered their survival for the first 16 weeks of life because that is when most mortality occurs. By the time hunting seasons comes around there is too few fawns left to reliably estimate a harvest rate. I have conducted 2 fawn survival studies and we did document hunting mortality, but the sample size is so small (# fawns still alive) by the time hunting season occurs our inferences are limited. This is the case for nearly all fawn survival studies.

Comments/Thoughts on
“and a spare”
So much of the world of nature seems to survive on the same premise, that is, have a spare. ( or have lots of spares)
Think of the high number of young and replacement among wildlife when good food and cover is abundant. Rabbits with numerous young and numerous litters per year, birds with lots of eggs in the nest at least once a year if not more times a year. Frog eggs in puddles. Plants seed production. How many acorns does an oak tree or a maple or aspen tree have to produce to replace it self and keep its linage going?
With deer it may often be one spare, and that one spare has populated and repopulated landscapes beyond what a lot of people expected. With many other life forms it’s more like, have lots of spares.
Also appears that the spare and lots of the spares were never intended to last a long time. Only a small percentage survive a few years in many cases. Is that what helps to keep the surviving ones so healthy?

Great content. Keep it coming!

Thank you. Good stuff!

Thank you. Good and interesting information.

Most folks seem to have a poor understanding of the life-time reproductive potential of a doe and that she only has to have one surviving offspring to replace herself. For a buck that may mate with multiple does, only a one of his many offspring has to survive to replace him. Of course some adult deer are sterile, others never have an opportunity to breed so a few more fawns have to live to replace those non-reproductive deer. But to have a stable population not many fawns have to live — or can live.

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