A new trend – late born fawns

Deer Researcher Duane Diefenbach received a curious email late in February. He heard from a rural mail carrier from Luzerne County, who had seen a group of deer. A fawn, still covered in spots, traveled with them.

Typically, the breeding dates for deer don’t change from year to year. Fawns are born 200 days later. I’ve seen spotted fawns while archery hunting in October, but have never seen one in February.

Diefenbach provided some interesting statistics. Fifty percent of females are bred by Nov. 13. That means that about half of all fawns are born by May 31.

But, that also means that half the females are bred after Nov. 13.

Let’s take that spotted fawn that’s seen in October and count backward.

If a fawn is conceived Jan. 7, it would be born July 26. It would still be nursing in October. Fawns are weaned at about 10 weeks.

At the extreme, the Pennsylvania Game Commission has documented fawns being conceived March 3. That fawn would not be born until late September. So, although seeing a fawn with spots in February is not impossible, it is not likely.

The phenomenon of late-born fawns in goes against Mother Nature. White-tailed deer and other animals have breedings that result in the proper timing of the birth – to occur during favorable environmental conditions.

“After fawns are weaned, summer is at its height and food is plentiful giving them time to get as big as possible going into winter,” Diefenbach said.

“Born too early and fawns are likely to succumb to springtime cold snaps; born too late and they are likely to die from winter weather.”

As you’d expect, as you move south there are different factors that influence birth dates. If the climate is fairly constant, the window of time for fawn births can be very wide. Texas is a good example, where fawn births are in time with period when forage is abundant, following periods of rain.

Can a late-born fawn survive? Yes. One of the most important things that must happen is growing a new “winter” coat. The coat gets thicker, but the spots aren’t shed, they stay visible.

Is it possible that rarity of late-born fawns will become the norm? Is it a result of climate warming?

“In this century, we are likely to see changes in the timing of births as our climate warms,” Diefenbach said. “Winters are becoming milder giving early- and late-born fawns a higher chance of survival than in the past.”

“Day length will continue to drive the timing of breeding in white-tailed deer – it’s in their genes,” he added. “But in ecology variety is the spice of life, and those females that get pregnant early or late are going to have a better chance for their genes to be passed on.”

(Some information for this story was provided by Deer Forest Blog, Deer Forest Study, Penn State University)