What is a Hibernaculum?

Eagle Scout, Chance, created some wonderful snake habitat and shares the process with us.

This summer, Bucks Audubon was excited to have Eagle Scout, Chance Trammell, join us to complete his Eagle Scout Project! He created wonderful snake habitat, called a hibernaculum. Learn more about his project below and come visit our grounds to see it in use!

What is a hibernaculum and why build one? 

A snake hibernaculum (plural = hibernacula) is an underground chamber where snakes can safely spend the winter protected from the cold. A hibernaculum can be a built structure, such as an old well or building foundation, or it can be naturally occurring, such as an animal burrow, rotten tree stump, or fissure in the bedrock. A good hibernaculum should be below the frost line to prevent snakes from freezing to death, be relatively humid to prevent snakes from drying out, but be above the water table to prevent snakes from drowning. A lack of natural hibernacula can be a major factor limiting snake populations. Building a snake hibernaculum can help replace hibernacula which have been lost due to urban expansion, intensive agriculture, deforestation and other forms of habitat loss. Adding hibernacula to the landscape also means that snakes may travel shorter distances to find a suitable wintering site, lowering the chances a snake may have to cross a road or encounter other threats. 

How is a hibernaculum made?

1. Select a well-drained site protected from cold winds, with good sun exposure (south-facing).  Ensure that surface and groundwater flows away from the site (i.e. build on upland areas).  If not, drainage pipes below the frost line may be required to prevent flooding. 

2. Your snake hibernaculum can be sized to fit the available space, but it must be deeper than the frost line (at least 2 meters deep).  Snakes prefer an overwintering site that is close to the water table, but not flooded.  Moist air ensures that snakes do not dehydrate over the dry winter months. 

3. Place rubble in the bottom to create chambers for the snakes.  Chambers created at different depths allow the snakes to move vertically and horizontally to select a preferred temperature/humidity microhabitat.

4. Concrete blocks or PVC drain pipes (with holes cut into the sides along the length of the pipe) can be used for entrances and passages to allow the snakes multi-level access.  Snakes use these passage ways to move to the bottom of the pit and into the underground chambers.  It is necessary to hand place the concrete blocks to ensure that a space or tunnel extends down into the bottom of the pit at each of the corners.  Continue to fill the pit with larger rocks, old concrete blocks and slabs, maintaining as many openings and chambers as possible. 

5. Cap with an insulating layer of smaller rock rubble.  Be sure to leave the entrances open and keep the top clear of shrubs that may grow as the site matures.

6. Protect emerging snakes from predators by having cover objects such as logs, rock piles, brush and uncut grass nearby. 

7. In the spring (mid April to late May), monitor your site to determine if wildlife are using the hibernaculum. Don’t get discouraged, it may take several years before snakes discover your hibernaculum.

Written by Guest Blogger, Eagle Scout Chance Trammell

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