Salt Marsh Voles Again. Part III. New Information

Back in 2010 I put up two blog posts about the Florida salt marsh vole, a unique and unusual inhabitant of the Lower Suwannee National Wildlife Refuge. The earlier posts can be found here and here. New information, new questions, and some ideas about answers suggest it is time for yet another series of posts. They begin with field notes from a paddling trip undertaken ten years ago, almost to the day.

 Field Notes: Long Cabbage Islands – September 25, 2011

I am beginning a paddling trip in the Gulf waters bordering the Lower Suwannee National Wildlife Refuge, with a group ground-truthing a series of kayak routes laid out on refuge waterways. While verifying the maps, we hope also to learn about important natural features to help in preparing informative narratives to go along with the maps.

We leave from the small gravel launch ramp at Shell Mound, glide past Hog Island—a chain of narrow islands that are the site of a prehistoric cemetery—and paddle north by northwest. Billowing clouds punctuate the bright blue sky, waves are minimal, and the view toward the horizon in every direction is stunning.

Despite the picture-perfect day, when we reach the Long Cabbage Islands, we find them underwhelming. Today the tide is relatively high, at 3.5 feet, and there is little to be seen that one could properly call islands. I would describe them as barely exposed sand dunes. Indeed, the tides tomorrow, on September 26 are forecast to be nearly 5 feet, and little of the islands should be visible then except for emergent spikes of smooth cordgrass (Spartina alterniflora) and occasional partly submerged black mangrove trees (Avicenna germinans). That these low islands are usually not completely submerged is attested to by a few mostly solitary cabbage palms (Sabal palmetto) clinging onto the highest patches of sand. Despite their precarious relationship with the open waters of the Gulf, the wispy, patchy islands are clearly not devoid of animal life. We see a few horseshoe crabs (Limulus polyphemus) copulating in the shallow water. And on the dunes are abundant shorebirds of several species, probably foraging for the countless horseshoe crab eggs that provide them with copious food. Other abundant animals are snails—marsh periwinkles (Littoraria irrorata)—we see on many of the stems of smooth cordgrass. These snails are said to always remain above the waterline except when venturing down below the surface to lay their eggs. Aware of this, I briefly wonder what they do when an unusually high tide overtops all the cordgrass stems.

Our return from the Long Cabbage Islands is uneventful. I think we will retain some pleasant memories of today’s paddle; it has been a great outing. The islands are a nice—or at least interesting—place to visit if not stay awhile. Importantly, the event has offered some interesting perspective on a marginal habitat that might be swallowed up with only minimal sea level rise.

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View of the Long Cabbage Islands showing their scant elevation. The cabbage palms (Sabal palmetto) and black mangrove (Avicennia germinans) trees seen in this image would be the only possible refuges available in severe storm surges.

 

Salt grass (Distichlis spicata) patch on the long cabbage islands. Thick mats of this grass are believed to be the primary environmental feature favored by the Florida salt marsh vole.

Despite the pleasantness of the visit to the Long Cabbage Islands, we felt no need to return. Other projects took center stage, and these islands were soon all but forgotten. 

That visit was to be forgotten for only a few months, however. The islands grabbed my attention when their name came up in a report of a survey underway by University of Florida scientists. They were looking for the endangered Florida salt marsh vole (Microtus pennsylvanicus dukecampbelli)—an animal formerly known from only two nearby locations also in Levy County, Florida. I knew about the project, knew some of the students and professors involved, and realized that the vole has an interesting story, much of which I had related in blog posts back in 2010.

 Studies culminating in 2013 were successful in finding voles in several new locations through a trapping technique that “captured” them photographically in an ingenious device able to verify their presence without the need to disturb them. Of interest to me was that the Long Cabbage Islands were an area in which voles and another rare animal and likely predator, the salt marsh mink (Neovison vison lutensis) were relatively abundant.