Barrier islands of the Virginia Coast Reserve are noted as highly dynamic and the small mammals which thrive on this 'high-speed real estate' are as dynamic in nature as the islands they inhabit. Oryzomys palustris (marsh rice-rat) is an effective disperser over water and occurs on 21 of the 24 islands whereas Peromyscus leucopus (white-footed mouse) is less effective and occurs on only 4 islands (Dueser, et.al.). During periods of hurricane or storm flooding from rising tides, there is limited habitat available for small mammals which can give rise to migration from island to island or island to mainland causing a dispersal of genes throughout the barrier island ecosystem. In some cases it can lead to an extinction of a species on an island or in other cases introduce a new species to an island.

In an effort to determine available habitat during flooding events, barrier island topography and elevation above Mean Sea Level, Global Positioning System technology is being employed in the static and kinematic modes to produce three-dimensional mapping of Myrtle, Ship Shoal, Smith, and Mockhorn islands of the Virginia Coast Reserve. Upon completion of GPS data collections, tidal data will then be incorporated into the mapping scheme which will provide modelling of barrier island inundation during major storm/flooding events enabling researchers to determine available habitat during these periods of 'disturbance.' Utilizing ArcInfo/Arcview, we hope to provide detailed mapping with the major focus on migration or extinction of small mammals.

Data collections on Myrtle and Ship Shoal are still in progress and the first mapping schemes should be available for viewing in early Spring 1996. As of December 1995, 300+ kinematic baselines have been processed for mapping purposes on Myrtle Island alone. Kinematic GPS points are collected on a 10 meter resolution in and around the permanent small mammal trapping grids located on Myrtle, Ship Shoal, Smith and Mockhorn islands. Additional points are taken according to island topography in order to provide accurate mapping information: shorelines, major dune formations and overwash areas are key data collection areas. Static points are collected in order to provide additional structure and integrity to the existing GPS Network as well as provide the repeatability of GPS data collections as the barrier islands rotate, move westward and/or roll over. Each static point leaves a permanent benchmark (some of our key benchmarks are driven to the point of refusal which is somewhere around 55-60 feet; some of our short-term benchmarks are usually marked with 1/2 inch rebar driven 20 feet) which is entered into the VCR/LTER GPS Network. Data collections are accomplished utilizing two Trimble 4000SE units with kinematic capabilities; post-processing is accomplished with GPSurvey 1.01 and Trimvec Plus.
There are some preliminary 2D and 3D topo maps that are utilized for 'ground-truthing' and working documents which are provided as a demonstration of mapping with GPS data; only 86 of the 300+ points on Myrtle were included in the topographic maps due to PC limitations. Those of us who have worked on Myrtle should gain orientation with respect to the small mammal grid and shoreline locations. Again, this is only a demonstration utilizing GPS kinematic points; ArcInfo/ArcView will be utilized in the final mapping stages.