We’ve all seen the state’s Deer Crossing signs. Obviously, deer have habitually crossed the road in that spot, and they’ve been hit by vehicles. Eventually it happens enough times and workers install a sign, hoping that motorists will be careful in that area.

But why do deer cross a road in a certain spot? In fact, why do they take the paths they do? Do things change seasonally? Do they change their habits in response to hunting pressure? Or new building construction?

I’m following with great interest the Deer Forest Study, launched in 2013 as a cooperative effort involving Penn State University, the Pennsylvania Game Commission, the U.S. Geological Survey and the Pennsylvania DCNR Bureau of Forestry. Researchers are combining efforts to collect and analyze data, with some special cases such as Doe 8101.

Doe 8101 was captured during 2013, the first year of the study. Researchers attached a radio collar and tracked her movements for the next five years. The study area includes portions of Rothrock, Bald Eagle and Susquehannock state forests.

Here’s something I hadn’t known about radio collars – when the battery life gets low, researchers can send a signal to the collar for a “drop” so that it will fall off the deer and be retrieved, while it’s still sending a weak signal. As Doe 8101 collar signal got low, researchers signaled the drop but never received a second signal, which would have notified them that the collar was dropped.

Ah well, researchers thought. Must have been a collar failure.

While they’d been tracking Doe 8101, she’d made an interesting annual big move – several kilometers - every March. Most of the year, she stayed in an area where there are ongoing timber harvests and plenty of good browse for food. But late every winter, she’d make that big move to the east of her regular home range.

Why? There are several possible answers, none of them definitive – the area to the east has a good southern exposure, and possibly snow cover is reduced there. For the five years her movements were recorded, she made that same move in March. The collar batteries for Doe 8101 were failing in January 2018, when the collar drop was attempted.

Then, by chance, her collar was found in a pond. Researchers feared Doe 8101 had been poached, and her collar dumped into the pond. As deer go, she was at least “middle-aged”, first collared at nearly 2 years old and about 7 ½ when the collar was found.

Then researchers got a treat, a happy coincidence. Doe 8101, still sporting her identifying ear tags, was caught on camera in September 2018. She had a fawn in tow. Has she taught her fawns to make the same move in March?

So why do deer use those same places to cross roads? Obviously, they have done it for generations, taught by wise old nannies like Doe 8101.