Precast Hellbender Shelters: The Bender Hut
Video of a Bender Hut in use in Virginia.
What is a "Bender Hut?" Simply put, it is an artificial shelter built for Hellbenders, made to replicate the cavity that is found under very large slab rocks and boulders (the Hellbender's preferred place to hide and nest).
The Bender Hut was originally developed by Jeff Briggler and John Ackerson at the Missouri Department of Conservation (Briggler, JT and JR Ackerson. 2012. Construction and use of artificial shelters to supplement habitat for Hellbenders (Cryptobranchus alleganiensis). Herpetological Review, 2012, 43(3), 412–416).
The MO DOC makes their Hellbender shelters using a chicken wire frame and concrete applied by hand. In 2012, I began working with Bluffton Precast Concrete and Norwalk Precast Molds to design a form that could be used to produce Bender Huts using precast technology.
The final product is being deployed into streams in Ohio and elsewhere in the range of the Hellbender. We see these structures playing potentially important roles in four aspects of Hellbender conservation activities:
1) As a survey technique. The moving of large rocks for conducting
surveys is not a benign activity. Rocks occupied by Hellbenders are normally embedded into the substrate, with only one small entrance that can be easily guarded. When a large rock is moved for surveying, it may be impossible to put back into place in a manner that makes it suitable for Hellbenders (i.e., no water flowing through; no light penetrating; only one entrance). More researchers are noting that Hellbenders often abandon rocks that have been moved, and inspections with underwater borescopes show that oftentimes rocks that have been previously moved no longer have suitable conditions for Hellbenders.
The Bender Hut can be checked for Hellbenders with almost no disturbance, thanks to the removable lid. This can allow for access to animals for surveying, collecting growth and demographic data, or conducting health assessments.
2) As a method for collecting eggs. The Ohio Conservation Plan for the Eastern Hellbender envisions the captive head-starting and repatriation of Hellbenders as one of the main techniques for stemming the decline of the species in the state (Lipps, G., C. Caldwell, and J. Navarro. 2012.Conservation Plan: Eastern Hellbender, Cryptobranchus alleganiensis alleganiensis. Division of Wildlife, 42p.). Implementation of this plan requires a supply of wild-collected eggs.
Until 2011, only one Hellbender nest had ever been located in the state. From 2012-2016, 18 nests under rocks and in bedrock crevices have been located, but this has required a great deal of time and effort, and the actual removal of eggs has been difficult.The Bender Hut will allow for easy access to Hellbender nests for egg collection.
3) As a research tool. Little is known about what goes on inside of a Hellbender nest. The male Hellbender remains with the eggs, but how long do the larvae remain in the nest after hatching? Does the male consume eggs or larvae? Is he transferring beneficial bacteria to the young? What is the water quality in the nest?
The Bender Hut will provide for opportunities to study Hellbenders in-situ as never before. The precast concrete hut includes a 2” PVC sleeve in the top of the hut that can be plugged when not in use, or can be used to insert a water quality meter or even plumbed to hold an underwater camera. There are many possibilities for increased research opportunities with the Bender Huts.
4) As a recovery tool. Siltation is widely regarded as the greatest threat to Hellbender habitat in Ohio and throughout much of its range. With increased siltation, available refugia (i.e., large rocks) become smothered and completely embedded making them unusable by Hellbenders.
While it is unknown how much the availability
of shelter rocks limits populations, it is not inconceivable that adding
artificial shelters could benefit populations much like Bluebird boxes did for
that species or could create corridors to connect genetically isolated
populations of individuals.
The Japanese Connection
While visiting Japan in 2010, researchers working with the Japanese Giant Salamander (a close cousin to the Hellbender) showed us the "Hanzaki Blocks" that are used to provide artificial shelters for that species. Unlike Hellbenders, Japanese Giant Salamanders utilize burrows in the banks of streams for nesting.
When streams are channelized or banks are reinforced, these burrows are often destroyed. To compensate, Hanzaki Blocks are often placed into the banks of the stream to provide nesting areas for the salamanders.
The Japanese Hanzaki Block serves many of the same purposes as that of the Bender Hut for the Hellbender. We greatly appreciate our colleagues in Japan for freely sharing their information and experiences in providing artificial shelters for giant salamanders.