Investigating the distribution, population status, and habitat requirements of the Wayne's Black-throated Green Warbler in the northern south Atlantic Coastal Plain
The Wayne’s Warbler (Dendroica virens waynei) is a unique, disjunct subspecies of the Black-throated Green Warbler that is restricted to the South Atlantic Coastal Plain from southeastern Virginia to South Carolina. The nominate form (D. v. virens) breeds in coniferous forests across the northern latitudes of North America and through the higher elevations of the Appalachians. The Wayne’s population is 500 km east of the nearest Appalachian population and 1,200 m lower in elevation. The Wayne’s form is smaller than the nominate race and has a distinctly smaller bill. The factors that lead to the isolation of the Wayne’s form from the nominate race are not known. It is possible that this subspecies was originally associated with the extensive stands of Atlantic white cedar (Chamaecyparis thyoides) within the region. For all practical purposes, these forests were harvested prior to the description of the Wayne’s form to science. No recent attempts have been made to assess the status, distribution and habitat associations of this subspecies. The two primary objectives of this field project were 1) to assess the general status and distribution of the Wayne’s Warbler within the northern portion of the South Atlantic Coastal Plain (particularly focused on FWS refuge lands) and 2) to determine if there are habitat elements that may help to explain distribution patterns. A network of 265 fixed-radius point counts was used to examine seasonal occurrence, spatial distribution, and patterns of habitat use by Black-throated Green Warblers. Survey plots were chosen to represent the full gradient of forest types within Great Dismal Swamp, NWR, Pocosin Lakes, NWR, and Alligator River, NWR. Plots were surveyed 7 times between early April and mid June, 2001. Detection patterns were used to develop a protocol for classifying plots as to occupation by breeding birds. Approximately one half of all plots were selected for vegetation measurements. Plots used for sub-sampling vegetation spanned the forest gradient and were evenly split between plots classified as breeding sites and plots classified as unoccupied. The Wayne’s Warbler is one of the earliest arriving and breeding neotropical migrants within the region. Detections of Black-throated Green Warblers began in early April, increased to a peak in late April and then declined throughout May and early June. Birds were detected during 251 (13.5%) of 1,862 point counts conducted. Detections were widespread and included 114 of 266 (52.6%) survey plots. During late April, birds were detected within 23% of all survey plots on Alligator River, NWR. Plots classified as breeding sites were highly clustered within Alligator River, NWR and were not identified within either the Great Dismal Swamp or Pocosin Lakes, NWR. Alligator River, NWR may support one of the highest breeding densities of this sub-species throughout its restricted breeding range. Forest composition had a significant influence on the distribution of breeding sites. The frequency of plots classified as breeding sites was higher than expected for plots containing loblolly pine (Pinus taeda), Atlantic white cedar, and bald cypress (Taxodium distichum). The density of these tree species within survey plots was significantly higher for plots classified as breeding sites compared to plots classified as unoccupied. This response was particularly significant when all three tree species were combined.