COMMENTARY BY DR. DAVE SAMUEL
Almost every November, I hear from a hunter who says he has seen a fawn that has spots. If such a post gets on one of the deer hunter Facebook pages, lots of other hunters reply that the rut has somehow changed. Does are now being bred later, so something is drastically wrong because if does breed later, fawns are born later and they’ll be small when winter arrives. When that happens, fawns will die and we’ll lose a lot of the fawn crop.
Well, this shows hunters love to talk about the rut. It also shows hunters care about deer, and are concerned about all these late drop fawns. However, I want to slow this “the sky is falling” freight train, and take a look at the science and what is really going on out there.
We know fawns are born around 200 days after the doe is inseminated during the November rut. We also know that the peak of the rut is determined by photoperiod, day length, and so it stays the same every year. Not all does read that book, and other factors such as weather can cause does to breed earlier than the peak or later than the peak, but most are bred in a one-week period between Nov. 10 and Nov. 17. Finally, we know that fawns lose their spots at 3-4 months of age.
Yes, hunters see bucks chasing does in late October, and some even see bucks mating does in early October and even into December. It happens, and in order to have a fawn that still has spots during the West Virginia gun season, it would have been bred in December or maybe even January.
Now that we have the basics, let’s talk about something called a bell curve. For almost any data set you can find in nature, there will be a bell curve that will explain that data. In our case, what a bell curve shows is most does breed within a one-two week period in November, but some breed before and after that period. The further you move from that central period, the fewer the number of does that breed.
Let’s look at the bell curve for many years of data showing the percentage of does bred by week in Pennsylvania. This graph came from data collected by Dr. Duane Diefenbach with Pennsylvania State University. I got it from his Deer Blog, a blog I’ve mentioned here often and one that every deer hunter should get and read. (Just Google The Deer Blog and subscribe to this weekly email post).
A bar graph that shows the bell curve relating to the percentage of female whitetails bred by week in Pennsylvania. The highest percentages shown indicate the most active breeding period known as the “rut.” ( Dave Samuel/For The Dominion Post)
From this graph, we can tell that lots of fawns are conceived between Nov. 5 and 19 in Pennsylvania. If we collected similar data in West Virginia, our bell curve would look the same. Notice the earlier we get into October, the fewer fawns are conceived and the later we get into December, the fewer fawns are conceived. It’s a bell curve.
Also notice the numbers trickle down as you go through December, into January and even February. In fact, one doe was impregnated the first week of March. How did that happen? Those really late conceptions are probably doe fawns that came into heat late their first year and got bred. That happens.
So most fawns are born by mid-June, but apparently a few are born in July, and even fewer in August. A fawn conceived in January will be born in July, and those conceived in February will be born in August. We’re only talking one or two from this Pennsylvania data, but it happens and it’s normal stuff.
So when you see a fawn with spots long after other fawns have lost their spots, it is no reason to believe something is wrong. Those fawns are just on the outer end of the bell curve. Being born late means their chance for survival drops if the winter is harsh, but that’s how Mother Nature works. She doesn’t care.
However, as Dr. Diefenbach points out in his recent “Winter Babies” Deer Blog, our weather is changing. Winters aren’t what they used to be, and that means that these outlier fawns will have a better chance to survive than they once did. Even so, that peak of the rut won’t change. And there my friends and fellow lovers of the outdoors, is your bell curve lesson for the week. The next time you see a fawn with spots in December or January, know that it’s not common, but perfectly normal based on the bell curve.
Dr. Samuel is a retired wildlife professor from West Virginia University. His outdoor columns have appeared, and continue to appear, in Bowhunter magazine and the Whitetail Journal. If you have questions or comments on wildlife and conservation issues, email him at drdave4@comcast.net.
