It is ondatra rat, Bill. A really soft material, with a massive under wool. From my point of view, it could easily be replaced by rabbit zonker strips :) It swims well, the muddler head is creating a lot of turbulens, that makes the zonker strip wiggle.
Here it's called muskrat. Thanks for clarifying this for me. I like the pattern a lot. Have to check to see if I can duplicate it with my stash of materials. If not, a rabbit Zonker will be substituted. Great look to it.
I've posted another picture of it, seen from another perspective. The body could be made of US tube instead. It's important to tie in some dubbing to help lifting the wing a bit. The most important part is the muddler head. It should only cover 3-5 mm of the tube and consist of 1-2 small stacks of deer hair.
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