Aquatic Mammal Scats

by Carl Strang

Soon after I started checking the amphibian traps I set in the marshes at Mayslake Forest Preserve I noticed signs that the traps were being used.

Mammal scats. The trap’s quarter-inch mesh gives a scale.

Other scats on nearby logs were drier, but about the same size.

They are composed of vegetable matter.

These are muskrat scats. Muskrats leave them on exposed surfaces just above the water, indicators to other muskrats that this marsh is occupied. I have known muskrats to construct rafts of cut plants when there were no readily available platforms.  This little marsh is showing itself to be home to quite a diversity of animal life.

Meanwhile, in the narrow stream nearby, I have noticed that a prominent rock likewise has been accumulating a mammal’s calling cards.

These are smaller in diameter than the muskrat’s scats, darker in color and in linear arrays.

A close look reveals what appear to be tiny fish bones.

The bones by themselves don’t rule out muskrat, but this is a narrow swift stream, and repeat visits here by a muskrat are unlikely. Also, other structural features in these droppings point to a different species.

These scats in fact reveal that the mink I tracked through the winter continues to pass this way frequently. I find it interesting that two aquatic mammals in different orders use similar behaviors to communicate their presence.

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