Distribution, population structure and habitat use of the endangered Saint Francis Satyr butterfly, Neonympha mitchellii francisci

American Midland Naturalist, The, April, 2008 by Daniel Kuefler, Nick M. Haddad, Stephen Hall, Brian Hudgens, Becky Bartel, Erich Hoffman

MOVEMENT AND COLONIZATION

Because Neonympha mitchellii francisci live in a shifting mosaic landscape where habitat is created and destroyed by fire, beaver activity and succession, movement is necessary to maintain their metapopulations. To enhance our understanding of butterfly distributions and colonization events, we used several types of data from MRR and observational studies. While conducting MRR studies, we recorded the transect location where each individual was first seen. We used a Trimble[R] GeoXM[TM] handheld with ArcGIS 9.0 (ESRI, 2004) to determine the length and location of transects used for population studies within sites. Movement distances within sites were categorized by the distances between transects from which the individuals were observed. Movement distances of individuals between sites were calculated as the straight-line distance between the two sites. We also used observational data of individuals occurring at previously unoccupied wetlands and of N.m. francisci found at areas distant from occupied wetlands to draw inferences about their colonization ability.

RESULTS

DISTRIBUTION

Our surveys show that the distributional range of Neonympha mitchellii francisci appears to be completely confined to Ft. Bragg. The absence of this species in other likely tracts of habitat throughout NC, including the Green Swamp, Holly Shelter Game Land, Camp Lejeune and the Croatan National Forest, has been confirmed by lepidopteron surveys conducted by the NC Heritage Program.

Even within Fort Bragg, the butterfly is highly restricted in its distribution. The total area of known, occupied habitat for Neonympha mitchellii francisci is about 10 ha. All observations have been made within just eight headwater drainages. These drainages are concentrated in just one area, with either their headwaters or mouths adjacent to one another across short divides. Including the two sites originally discovered by Parshall and Kral (1989) N.m. francisci have been observed at 31 sites within these drainages.

We have recorded Neonympha mitchellii francisci at 16 sites outside of restricted, military training areas (Table 2). Of these, only four have been occupied by subpopulations over the entire course of our study. The other 12 sites currently do not support subpopulations of N.m. francisci, although individuals have been occasionally seen at several of them over the last ten years. These include degraded sections of peripheral wet habitats near existing sites that once supported subpopulations, potential high-quality sites where the butterfly had never been previously recorded and sites where known populations have gone extinct. In restricted areas, we know of 14 subpopulation sites on five different watersheds. These 14 sites were all discovered during the original status survey for this species, but have been rarely visited since.

HABITAT ASSOCIATIONS

All populations that we studied are associated with successional wetlands located in the floodplains of small headwater streams. Although quite wet, these habitats are only intermittently flooded. Vegetation consists of a mixture of shrub thickets dominated by alders (Alnus serrulata) and transgressive swamp blackgums (Nyssa biflora), red maples (Acer rubrum) and open areas dominated by sedges, grasses, rushes, sphagnum and other wetland herbaceous species