Potential traces everywhere

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I haven’t had a lot of free time over this summer, what with moving across the country and starting a new job. Even so, I’ve been slowly working my way through an excellent book on traces and trace fossils, “Life Traces of the Georgia Coast” by Anthony Martin (@ichnologist on Twitter). Due to the insidious influence of this book, I now find myself looking for traces all the time.

A few days ago when I was leaving work I spooked a rabbit (probably a desert cottontail, Sylvilagus audobonii) that was hiding in the grass beside the museum. Having just read the chapter in “Life Traces” that included rabbit traces I decided to see if this rabbit had left behind any evidence of its presence.

Most of the Western Science Center grounds are landscaped with native, drought-resistant vegetation. The grasses along the edge of the building are mostly deergrass (Muhlenbergia rigens), a bunchgrass that grows in dense clumps, and when I saw the rabbit it was running from a patch of deergrass. When I saw the grasses from above, I noticed that the middle of some of the clumps were brown and missing blades (top). Here’s a closeup of the middle of one of the clumps:

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The center of the clump was covered with mashed-down, broken blades of grass, over an area of roughly 25 cm by 10 cm. Around the margin of the flattened area there was a dense patch of erect bases of grass blades, clipped off to a height of around 10 cm. The clipped grasses were concentrated on each side of the flattened area, so that the flat area was mostly open on each end of the long axis.

A quick survey showed that about 1/3 of the deergrass bunches had these patches in their centers, although there was a lot of variation in their size, and especially in the amount of clipped-off blades. Some patches had only a very small number of clipped blades, although all of them had at least a few. It’s interesting that these clipped and flattened areas are only visible when seen from above. When seen from the side the tall grass around the margins of the clumps hide the flat patches at the center.

I suspect that the rabbits are eating out the centers of the clumps and using them as hiding places. A rabbit hunkering down in the center of a clump would be completely invisible to predators like coyotes, and while a rattlesnake might be able to sense the rabbit’s body heat it might have a hard time finding a way into the center of the clump.

So far I haven’t found any additional traces to confirm my interpretation. I haven’t spotted any rabbit fur or droppings in the clumps (and I’m a little hesitant to stick my hand into them blind, because of the possibility of the aforementioned rattlesnakes). Hopefully one day I’ll get better confirmation, like actually seeing a rabbit sitting in the clear patch, chowing down on deergrass.

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