A friend game me a challenge a bunch of years ago of finding any spot in the woods, sitting down, and not getting up until a I found a wild animal hair’s within arm’s reach. It was a great challenge, and on my first attempt took me about an hour to complete (it’s possible that the hair I found may have been one of my own). I often think about the ubiquity of lost hairs when out tracking animals in the woods, especially in the spring when some fur bearers molt. This weekend I came across a trail of deer tracks littered with fur and wondered just how hard this challenge is. So this week I’ll describe your odds of finding a deer hair in the woods and next week I’ll describe why deer hair is amazing. More on this below, but first a couple of exciting announcements!!

Fun maths

So back to the challenge of finding an animal’s hair while sitting somewhere in the woods. It turns out the chances of sitting down on a wayward strand of deer fur is surprisingly high. Deer fur density is significantly higher in the winter than summer, possibly as high 5,000 guard hairs per square inch (guard hairs are the outer layer of fur that gives the animal its color; the underfur on deer is about 5x as dense as the guard hairs)! All of this fur is molted twice a year, once in the fall to prepare for the cold winter months, and again in the summer to replace the thick winter coat, with a cooler summer coat (see molting moose below).

For the calculation, I needed not just the density of fur, but also a rough estimate of the surface area of a deer. Unfortunately, I didn’t have much luck getting specific numbers here, but I did find a website that sells 50″ long and 25″ wide deer hides. Those dimensions don’t include the entire animals fur-covered portions, so we can round up to ~10 sq ft on the whole deer. That yields a total of about 50,000 guard hairs per deer and another 250,000 smaller insulative hairs in the underfur. Again, deer molt twice per year, once in the fall and again the spring so we double that for total hairs molted per year for 600,000 hairs (see assumptions at the bottom for why this isn’t a great assumption).

Now we need to know how many deer we have. While not as high as Wisconsin’s deer density (as high as 80 deer per square mile), Vermont has about 15.6 deer per square mile (more on deer density). Let’s get our variables and units in order:

  • 600,000 hairs per deer shed per year
  • 15.6 deer per 27,878,400 sq ft

Now we’re ready for some quick math:

Hairs per square foot = (600,000 hairs per deer * 15.6 deer) / (27,878,400 sq ft)

= .34 deer hairs per square foot

With ~1 deer hair ever 3 square feet, I should definitely be within arms reach of a deer’s hair anywhere I sit down in the woods. Now combine these odds with the molts from raccoons, squirrels, mice, beavers, foxes, skunks, shrews, bats and all the other mammals and it’s incredible that we aren’t just sitting on a blanket of fur as thick as the leaf litter!!

Roadside moose with patchy fur from the spring molt (Alaska)
Some assumptions

This isn’t the cleanest of math, and I definitely made some assumptions that affected the total calculation:

  • the same number of hairs are shed in the fall and spring (600,000 is high because fur is less dense in the summer coat)
  • the deer are evenly distributed throughout Vermont (they’re not, we have more in the suburban areas of Chittenden Co than in the high parts of the Green Mountains)
  • the fur gets evenly distributed throughout the forest (it doesn’t, tends to concentrate along trails and where the deer bed down at night)
  • the fur only lasts 1 year before it decomposes (it doesn’t, tends to last much longer)
  • all of the fur is shed in each molt (I actually don’t know the answer to this. They don’t lose all their fur at once – it happens patchwork – but couldn’t find anything to confirm that the deer lose all their fur twice per year)
Wilson's warbler nest lined with moose hair (5 eggs)

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