No Floaties Required aka Mammal Profile Vol. 3: The Marsh Rice Rat

Despite Hurricane Sandy's best efforts, Eastern Shore of Virginia has survived the strong winds and the high waters. Power was only lost temporarily, and the flooding was minimal. To many this may be surprising, but the Virginian section of the Delmarva Peninsula still has many of its natural fortifications. Almost all of the barrier islands off the coast are wilderness, and there are expansive salt marshes between the shore and the islands--not to mention extensive oyster and shellfish beds. All of these reduce wave motion and act as a shield to hurricanes. This is a fine example of ecosystem services, processes which ecosystems perform that benefit humans.

Compared to Norway rats and black rats (the invasive beast and

the grungy city-dweller, respectively) The marsh rice rat is a rather handsome rodent.

But, the real reason we are here is because we want to learn about the robust, ever-versatile marsh rice rat (Oryzomys palustrus, "Marsh/Swamp Rice Mouse"). As it is semiaquatic, these mid-sized rodents flourish in marshes and the Atlantic coastal plains. Their distribution ranges from Texas through the Southeast and some parts of the Midwest, up to New Jersey.

Marsh, marsh edges, and the surrounding uplands all are likely

places to find this species. Here, my colleague J. Sparks works along

one of the trapping lines. 

As their name suggests, they are bountiful in all types of marshes (saltwater and freshwater), and are able to swim great distances, sometimes holding their breath underwater for long periods of time. The longest I have counted so far is 17 seconds. On the barrier island system they have been reported to swim distances greater than 50 meters across deep channels, no easy feat for an animal that is usually smaller than a soda can. Because they are a truly hardy species, the presence of the marsh rice rat is almost the "100% guarantee" of small mammal trapping on the barrier islands we are surveying. Even on islands that are constantly shifting or are barely an island at all, a rice rat will be present. Thus, they are important players in understanding biogeography, the discipline that tries to understand how populations of species vary and function over different landscapes.

After taking measurements, this guy went on a nice underwater swim and hid in the grasses.

Another rat wanted to demonstrate its swimming abilities for the camera. Given that water

causes rapid temperature loss, it is curious to think about how these rodents survive during

colder months after being submerged. It probably has significant energy consequences.

Marsh rice rats are true omnivores and will generally eat most things they come across: plants, seeds, snails, insects, fiddler crabs, mollusks, and some eggs of marsh-nesting birds. They also are an important food  for marsh hawks, owls, snakes, and mammalian predators such as fox and mink. Thankfully, they are not too much of a hassle for human beings. Because of their habitat preferences, they rarely infringe on human endeavors and become pests.

Unfortunately, these animals are quick, and this is the only natural picture I have been

able to capture. These species are also gutsy, inhabiting grassy dunes and making sprints

across open sand.

Sources
Linzey, D.W. 1998. The Mammals of Virginia. The McDonald & Woodward Publishing Company: Blacksburg, VA.
Moncreif, N.D. and R.D. Dueser. 1994. Island Hoppers. Virginia Explorer 10(4): 14-19.
Webster, WM. D., J.F. Parnell, and W.C. Biggs, Jr. Mammals of the Carolinas, Virginia, and Maryland. The University of North Carolina Press: Chapel Hill, NC.

Settling Down and Shoring Up

Well, it has taken me a while to write another post, but I am back! My position at the refuge in New Jersey wrapped up nicely, and I have settled into a new job on the Eastern Shore of Virginia.

The Eastern Shore, formally known as the Delmarva Peninsula, has the Chesapeake Bay 

to the West and the Atlantic Ocean to the East. Note the barrier islands. Image from Google Earth.

The project I am working on is part of the Virginia Coastal Reserve Long-term Ecological Research (VCR-LTER) initiative. While this initiative has a variety of components, I am specifically working on small mammal surveys (voles, mice, shrews, rats) with a professor who has researched the shore's ecosystems for many years.

The project will take place across the shore: 2 mainland sites and 19 or so barrier islands. Part of the study will compare small mammal diversity to surveys conducted approximately 20 years ago. Having a benchmark of the species currently found on the islands will also provide good reference for similar studies conducted in the future. The barrier islands provide many ecosystems services, and they are rapidly changing in habitat composition and size. Thus, the small mammal work will help in understanding the biogeography and ecology of the greater barrier island ecosystem.

My colleague, J. Sparks, working on reinforcing trap boxes, attaching straps,

and soon to be waterproofing them. Each box holds 32 folded traps.

Before trapping can occur though, the equipment had to get arranged. As some sites will have upwards of 200 traps, solid preparation is key. The type of traps used are collapsible Sherman live-traps, which are are effective at capturing small mammals and also are a survey method that have relatively high capture rates.

Getting everything together involves preparing trap boxes to carry them in, cleaning the traps, making sure all parts of the traps function, and creating the baits for the traps. Normally, baits for these traps are peanut butter and a grain (like rolled oats); however, our trap baits are a combination of shortening (Crisco) and cracked corn, both of which are easy to digest by the animals and also reduce trap mortality during cold temperatures.

Extra baits will be used for trick-or-treaters on Halloween.

They look close enough to candy. Just kidding.

 Using a GPS to mark the beginning of a transect and to

set a bearing. Then the line is laid and flagged.

Before traps are armed and ready for critter abduction, they are laid in transects (lines) that run through multiple habitat types to survey all small species at a location. Traps are then fixed open and baited to attract but not capture the mammals. Once they have acclimated to the presence of the traps (~48 hours) the arming of the traps ensues (and the results of those endeavors will be shared later!). All animals captured are released after measurements are taken.

 The bait is hung inside the trap from the back door, forcing the animal

to walk generously on the treadle which trips the front door. For baiting,

a tongue depressor is used to prevent the closing of the front door.

 Complete with holly and pine-straw landscaping, here is what the

Sherman trap looks like all set up.

On the next post I will begin the first of many species accounts from the animals we capture during the surveys.

Sources
Dueser, R. D., W. C. Brown, G. S. Hogue, C. McCaffrey, S. A. McCuskey, and G. J. Hennessey. 1979. Mammals on the                       Virginia barrier islands. Journal of Mammalogy 60:425-429.
Dueser, R. D. and W. C. Brown. 1980. Ecological correlates of insular rodent diversity. Ecology 61:50-56.
Schemnitz, S.D., 2005. Capturing and Handling Wild Animals. In C. Braun (Ed.).Techniques for Wildlife                                                 Investigations and Management (pp.239-285). Sixth Edition. The Wildlife Society: Bethesda, MD.