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Wednesday, May 18, 2011

Last Bear Den Measurements of the Season...

I spent the first day of "summer vacation" taking measurements from a few of the bear dens we were unable to get to earlier. These dens have been empty for over a month now but we still wanted to gather data on their dimensions and make-up. I will feature the most unusual den here:

Measuring dimensions of a
black bear den (5/11)
This den was unusual for two reasons. First, it was constructed by hollowing out a portion of an old round bale of hay. The bale had sat for a few seasons and was wet and grown over. The den was discovered by a man looking for shed antlers in March. The bear that made this cozy den was a female and she had three cubs. My students and I were unable to take the measurements when the DEC visited the first time to collar the adult and weigh the cubs. In this first photo, Erin Lord, recent FLCC graduate, is measuring the height of the cavity created by this bear. I took a few steps back when snapping this photo in order to show the cover associated with this den. Remember though, that when the bear was using this comfy straw house, there was no greenery present.

The next few photos give a real sense of what this bear chose/created for her and her cubs.

Measuring the height of a
bear den excavated from hay bale (5/11)

Here, Erin measures the height of the entrance. You can see the hay here from the old round bale. Can you also tell that there is a depression beyond the lip of the opening? In other words, the den entrance was smaller than the excavated cavity.

Measuring the depth of a bear den (5/11)

Well, field work isn't always comfy-cozy. Here Erin has to reach in to the back of the den while reading the tape measure to determine depth of the den. It was raining. There were many thorns. And although it is very unlikely that a bear would reuse a den, I am reluctant to modify the surroundings. I could have gotten a better photo by removing that vine in the foreground, but we made the decision to leave the dens as we found them.

Sizing up a bear den (5/11)

What we DID decide, was that there was no problem leaving our scent all over (and inside) the dens since we are many months away from any bear needing a den :)

Black bear den in close proximity to an active rail line (5/11)

The second factor that made this den unusual was how close it sat to a set of train tracks. I paced it off at 45 feet from the den to the rail. In this photo, the den is immediately behind Sasha, Jeb and Erin. The south side of the den was bordered by a corn field. 

Train passing a black bear den (5/11)

As we were remarking on what it might be like to den so close to a set of train tracks, we heard a distant whistle. As the train passed, we felt the deep rumble through our feet and I imagined what it felt like for the bear and her cubs every time a train passed. What did they make of it? Were the trains running when she selected this site? Was the lure of that soft bed a fair trade off for the multiple disturbances? Speaking for myself, I would rather have the peace and quiet....


  1. I found a fox den in an old hay bale a couple of years ago but never a bear den.

  2. Fascinating,i thought bears would only den underground amongst rocks.......

  3. Black bears in our area often use brush piles for dens, with a varying amount of modifications (such as excavating a depression or bowl, bringing in nesting material such as stick and leaves, etc.). Two dens this season were excavated directly in the sandy soil. Others have used hollow logs, leaf piles, a crawl space under a cabin and we even had a large male den completely in the open once. I saw a photo once of a bear that spent the winter high in a tree in a bald eagle's nest. Pregnant females seem to be the most selective when choosing a den site as they need protection for when their cubs are born. Females also den earlier than males on average.


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