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2011 SOUTHEASTERN NATURALIST 10(2):333–344
Status and Habitat Use of the Wayne’s Black-throated
Green Warbler in the Northern Portion of the South
Atlantic Coastal Plain
Bryan D. Watts1,*, Barton J. Paxton1, and Fletcher M. Smith1
Abstract - Dendroica virens waynei (Wayne’s Warbler) is a unique, disjunct subspecies of
Dendroica viren virens (Black-throated Green Warbler) that is restricted to the South Atlantic
Coastal Plain from southeastern Virginia to South Carolina. We surveyed a network of
265 fixed-radius plots 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 the region. Plots were surveyed 7 times between
early April and mid-June, 2001. 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 1862 point counts conducted. Detections
were widespread and included 114 of 266 (52.6%) survey plots. 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 Pinus taeda (Loblolly Pine),
Chamaecyparis thyoides (Atlantic White Cedar), and Taxodium distichum (Bald Cypress).
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.
Dendroica virens waynei Bangs (Wayne’s Warbler) is a unique, disjunct subspecies
of Dendroica virens virens (Gmelin) (Black-throated Green Warbler)
(AOU 1957, Bangs 1918). The nominate race breeds in coniferous forests across
the northern latitudes of North America and through the higher elevations of the
Appalachians (Morse 1993). The Wayne’s form is smaller than the nominate race
and has a distinctly smaller bill. Wayne’s Warbler has a much smaller breeding
range and is restricted to the South Atlantic Coastal Plain from southeastern Virginia
to South Carolina. Along much of this range, the population is confined to
a fairly narrow band within the outer coastal plain (Sprunt 1953). This population
is 500 km east of the Appalachian population and 1200 m lower in elevation.
The factors that led 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 Chamaecyparis thyoides (L.) B.S.P. (Atlantic White
Cedar) that were once an important component of the region’s plant community.
These stands were similar in form to the coniferous forests where D. v. virens
currently breeds. Wayne’s Warbler appears to reach its highest density from
southeastern Virginia through northeastern North Carolina. This region was the
1Center for Conservation Biology, College of William and Mary and Virginia Commonwealth
University, Williamsburg, VA 23187. *Corresponding author - firstname.lastname@example.org.
334 Southeastern Naturalist Vol. 10, No. 2
former location of the most extensive tracts of white cedar (Ashe 1894). More
than 100,000 acres of this habitat were harvested in the area in the late 1800s and
early 1900s for the shingle industry. This event virtually eliminated this unique
plant community from the region. The vegetation that has reclaimed many of the
historic sites after harvest is dominated by hardwoods rather than white cedar
Most of the extensive stands of Atlantic White Cedar were harvested prior to the
description of the Wayne’s form to science. How much the current pattern of habitat
use (and our perceptions of habitat requirements) is influenced by the absence
of white cedar is unknown. In the latter half of the twentieth century, the Wayne’s
subspecies has been suggested to utilize the entire gradient of forest types from
Atlantic White Cedar to Taxodium distichum L. (Bald Cypress) to mixed deciduous
forest (Meanley 1977; E.F. Potter, North Carolina Museum of Natural Sciences,
Raleigh, NC, unpubl. data; Sprunt 1953). The population has also been suggested
to have a close association with non-alluvial cypress swamps.
No recent attempts have been made to determine the status and distribution
of Wayne’s Warblers within the core of their breeding range (i.e. southeastern
Virginia, coastal North Carolina). Once suggested to be a fairly common breeding
species within the Dismal Swamp (Meanley 1977), researchers now suggest
that they have disappeared over the past 10–15 years from the northern portion
and have declined substantially in the southern portion (B. Meanley and D.
Schwab, Great Dismal Swamp National Wildlife Refuge, Suffok, VA, unpubl.
data). No attempts have been made to clarify the influence of forest composition
on distribution. 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 US Fish and
Wildlife Service [FWS] refuge lands), and 2) to determine if there are habitat
elements that may help to explain current distribution patterns.
We conducted this study within the Alligator River National Wildlife Refuge
(NWR), Pocosin Lakes NWR, and Dismal Swamp NWR (Fig. 1). These properties
are located within the coastal plain of southeastern Virginia and northeastern
North Carolina. Alligator River and Pocosin Lakes NWRs are located on the peninsula
of land bounded to the north by the Albemarle Sound and to the south by
the Pamlico River. The Great Dismal Swamp is located east of the Suffolk scarp
and west of US Route 17.
We established a network of 265 survey plots distributed throughout the broad
study area. The network included 154 plots on or within the vicinity of Alligator
River NWR, 83 plots on or within the vicinity of Great Dismal Swamp NWR,
and 29 plots on Pocosin Lakes NWR. We clustered survey plots in “mini-routes”
(groups of 20–30 points) to maximize survey efficiency. We assessed potential
field sites during March of 2001. Information was collected through a combination
of road surveys, aerial photographs, and meetings with refuge personnel.
During this phase, we attempted to 1) determine the distribution of forest types
2011 B.D. Watts, B.J. Paxton, and F.M. Smith 335
targeted within the study, and 2) evaluate survey efficiency of various field options
(i.e. assess roadway condition and access and evaluate site clustering).
We chose sites in late March that were accessible and could support a cluster of
20–30 point-count locations.
We based final selection of study plots within larger areas on forest type.
Target forest types represented the full forest gradient within refuge lands.
Categories included: 1) PPP = Pinus serotina Micheaux (Pond Pine) pocosin,
2) HDWD = hardwood dominated, 3) MIX = pine/hardwood mix, 4) PIN = pine
dominated, 5) CED = white cedar component, and 6) CYP = Bald Cypress component.
Tall pocosins with Pond Pine form over relatively shallow peat deposits
and are characterized by high above-ground plant biomass. Characteristic plant
species include Liquidambar styraciflua L. (Sweet Gum), Acer rubrum L. (Red
Maple), Ilex glabra L. (Gallberry), Leucothoe racemosa L. (Fetter Bush), and
Myrica cerifera L. (Wax Myrtle). Hardwood-dominated plots were those where
Figure 1. Map of study area. Black areas indicate conservation lands containing all survey
plots. The number of survey plots by geographic area was 154, 83, and 29 for Alligator
River NWR, Great Dismal Swamp NWR, and Pocosin Lakes NWR, respectively.
336 Southeastern Naturalist Vol. 10, No. 2
an estimated 75% or more of the canopy-forming stems were hardwood. Most
abundant trees included Red Maple and Sweet Gum. Mixed pine/hardwood plots
had relatively even numbers of Pinus taeda L. (Loblolly Pine) and hardwood
stems. Pine-dominated plots were those where an estimated 75% or more of the
canopy-forming stems were Loblolly Pine. White cedar plots were those that
contained at least a minor component of white cedar trees. Bald Cypress plots
were those containing at least a minor component of Bald Cypress. It was not
possible to locate an adequate sample of plots that were dominated by either
white cedar or Bald Cypress. Initial selection of forest types for plot placement
was done by visual inspection of forest composition (Table 1). Due to the unique
character of the three refuge properties, balance of forest types by geographic
area was not possible (Table 1). We established survey plots in late March and
early April. We positioned plots along roadways with a minimum separation of
We used a fixed-radius point-count technique to measure bird density and
frequency of occurrence. A survey plot (point count) consisted of a 50-m radius
circle with a wire flag located at its center. We conducted surveys along roadways
with the plot centers positioned at the road edge. The plot was split in half along
the road axis. Birds detected within the 50-m radius plot were recorded either as
within the focal half or within the remainder. We used birds detected within the
focal half of plots for habitat comparisons.
Bird surveys were conducted by a single observer standing at the plot center
and counting all birds seen or heard within a 5-min period. Birds detected were
stratified according to time, period, and location. We subdivided the count periods
into an initial 3-min period and a subsequent 2-min period. We recorded
birds as either within or beyond the 50-m radius. We conducted plot surveys in
11-d time blocks, where all points within the network were surveyed within each
block. We completed seven survey rounds between 8 April and 12 June 2001.
Plots covered by individual observers were rotated between time blocks to disperse
any observer bias. We alternated the order of surveys within “mini-routes”
between time blocks to reduce the impact of time-of-day effects. We conducted
surveys between 0.5 and 4.5 hrs after sunrise on days with no precipitation and
wind speeds of less than 24 kph.
Table 1. The number of survey plots by habitat type and geographic area.
Habitat type Pocosin Lakes Alligator River Great Dismal Swamp
Pond Pine pocosin 27 5 0
Hardwood dominated 2 18 31
Pine/hardwood mix 0 49 12
Pine dominated 0 31 9
Cedar component 0 28 21
Cypress component 0 23 10
2011 B.D. Watts, B.J. Paxton, and F.M. Smith 337
We measured vegetation structure/composition within a sub-sample of “occupied”
and “unoccupied” (with respect to breeding Black-throated Green
Warblers; see below) survey plots. Selection of survey plots for sampling was
based on occupation, habitat type, and geographic area. We attempted to balance
samples between habitats and refuges. We included all habitats in the selection
except Pond Pine pocosin, as no birds were detected within this habitat type
during the course of the study. Since this habitat type was concentrated within
Pocosin Lakes NWR, no samples were taken from this property. We measured
vegetation between 27 June and 26 July 2001.
We sub-sampled vegetation within two plots established within each 50-m
radius survey plot. We stratified each sub-plot to include a 5-m-radius plot embedded
within a larger 11.4-m-radius plot. We took vegetation samples from the
focal half of the survey plot. We positioned the center of each vegetation plot
30 m from the center of the point count in two different directions (each >90°
apart). The initial direction for the first vegetation plot was chosen randomly
from the center of the point count.
We collected vegetation data on two different levels within circular plots. We
counted all large woody plants (>8 cm dbh) and dead standing stems (snags) by
species and stem-diameter class (diameter classes included 8–22, 23–38, and >38
cm dbh), and estimated canopy cover and canopy height over the entire 11.4-mradius
plot. We used a convex densiometer to estimate percent canopy cover and
a clinometer to measure canopy height. We collected data on understory vegetation
within the 5-m-radius plot. We stratified counts of understory vegetation to
include stems, shrubs, and saplings >0.5 m in height and <8 cm dbh.
Breeding sites. Identification of breeding sites for Wayne’s Warblers using
point-count data alone was complicated by several opposing factors. The first of
these is the potential for overlap between the two subspecies (D. v. virens and
D. v. waynei) within the study area. The Wayne’s subspecies is one of the earliest
arriving neotropical migrants within the region. Within the study areas, individuals
begin to arrive on breeding territories in late March to early April (Meanley
1977). At this time, most D. v. virens individuals are believed to be still on winter
territories (Morse 1993, Sprunt 1953). Dendroica v. virens does not migrate
through comparable latitudes until mid-April. There remains confusion as to
whether or not and the extent to which D. v. virens migrates through the breeding
range of D. v. waynei. Some authors suggest that D. v. virens winters primarily
within Central America between Mexico and Panama and that most individuals
migrate north via a land route through Mexico and Texas, then continue on an
inland track to the Appalachians and northern breeding areas (Morse 1993, Oberholser
1974, Stevenson 1957). This route suggests that the probability of contact
between these two subspecies in the spring would be low. If true, virtually all of
the individuals encountered within the study areas would be D. v. waynei. This
view is supported by Sprunt (1953), who indicates that records of D. v. virens are
completely absent from the south Atlantic Coast and suggests that D. v. waynei
likely winters in a distinct location that is in closer proximity to the breeding
338 Southeastern Naturalist Vol. 10, No. 2
grounds. It has been suggested that D. v. waynei winters in western Cuba (AOU
1957). However, other authors (E.F. Potter, unpubl. data) who have worked
within the study area suggest that D. v. virens does move through the region,
although there is no suggestion as to the winter origin or breeding destination of
such individuals. The primary differences between D. v. virens and D. v. waynei
are bill and body size (Bangs 1918). There are no song or appearance differences
that would allow for simple separation in the field (Morse 1993, Sprunt 1953). At
present, there is no way to determine the subspecies designation of birds detected
within the area between mid-April and early May. Birds detected from late March
through mid-April may clearly be assigned to D. v. waynei due to subspecific
differences in the timing of migration. Birds detected after the first week of May
may also be assigned to D. v. waynei because by then D. v. virens are likely all on
their breeding grounds.
A second complicating factor is the early breeding season of D. v. waynei and
the rapid diminution of singing. The Wayne’s subspecies is one of the earliest
nesting neotropical migrants within the region. Nests with eggs have been documented
within the Great Dismal Swamp as early as 4 April (Meanley 1977). E.F.
Potter (unpubl. data) observed a marked decline in singing apparently related to
the hatching of eggs. Singing is not common after mid-May. This pattern suggests
that there is a considerable reduction in detection probability through the
month of May. The implication is that although birds detected in May could be
definitively assigned to D. v. waynei, the probability of detecting breeding birds
is much reduced.
In light of the factors outlined above, we developed rules for assigning occupancy
status to survey plots based on point counts. We analyzed detection
patterns to facilitate this process. We delineated three occupancy classes including
1) breeding location (occupied), 2) potential breeding location, and 3) no
breeding location (unoccupied). We considered sites to be breeding locations if
birds were detected after mid-May or where birds were detected during 3 out of
the 7 survey rounds. Analysis of detection patterns illustrated that these conditions
were related. Virtually all points having at least 3 separate detections also
had detections after mid-May. This level of consistency supports the contention
that these represent breeding locations. We considered sites to be potential breeding
locations if fewer than 3 detections were made with all detections prior to
mid-May. We considered sites to be unoccupied if birds were never detected.
Vegetation parameters. We derived several parameters describing vegetational
structure from vegetation sub-samples. These included mean canopy height
(CANH), % canopy cover (CANC), canopy tree density (CAND), sub-canopy
tree density (SUBD), sapling density (SAPD), and understory density (UND)
(Table 2). We did not include floristic information in the analysis, with the exception
of canopy composition. We derived parameters separately for the density
of hardwood, pine, white cedar, and Bald Cypress stems that were >22 dbh. We
compared vegetation parameters between sites that were classified as occupied
and unoccupied. We excluded potential breeding sites from the analysis.
Analysis. Due to the relatively small plot size, variation in breeding density recorded
was very low. Incidences where multiple individuals were detected within
a single plot were rare. For this reason, we assessed temporal and geographic
2011 B.D. Watts, B.J. Paxton, and F.M. Smith 339
patterns using frequency of occurrence where survey plots were the statistical
units. We evaluated potential relationships with vegetation characteristics by
comparing mean values using site-occupancy class (occupied vs unoccupied)
as the grouping parameter. We used Kilmogorov-Smirnov tests to compare
distributions relative to normality for each vegetation parameter. We transformed
all non-normal parameters using three standard functions (including log[X = 1],
[X]1/2, and arcsine [X]) and retested. We evaluated significance between occupied
and unoccupied survey plots using an F-test for all parametric variables and
Mann-Whitney U test for all nonparametric variables.
We encountered 335 Black-throated Green Warblers during point counts. We
detected birds during 251 (13.5%) of 1862 point counts conducted. Detections
were widespread and included 114 of 266 (52.6%) survey plots.
Detections of Black-throated Green Warblers were not evenly distributed
among survey rounds (Fig. 2). A substantial number of detections were made in
the first survey round, indicating that earliest arrivals were prior to the beginning
or during the first round. Work within the area leading up to the first survey
suggests that birds began to arrive approximately 2 days prior to the initiation of
the first round. Detections increased during the month of April, reaching a peak
in late April to early May. At this time, birds were detected within 23% of all
survey plots on Alligator River NWR. It remains unclear if this peak represents
Table 2. Description of structural vegetation parameters measured within survey plots within Alligator
River NWR and Great Dismal Swamp NWR (June–July 2001).
Understory density (UND) Density (n/ha) of woody stems and shrubs >0.5 m in height and
<8 cm dbh. Estimate from two 5-m radius plots.
Sapling density (SAPD) Density (n/ha) of tree stems >0.5 m in height and <8 cm dbh.
Estimate from two 5-m radius plots.
Sub-canopy density (SUBD) Density (n/ha) of tree stems between 8 and 22 cm dbh. Estimate
from two 11.4-m radius plots.
Canopy density (CAND) Density (n/ha) of tree stems >22 cm dbh. Estimate from two
11.4-m radius plots.
Canopy height (CANH) Average height (m) of canopy-forming stems. Estimate from 4
samples measured with clinometer within survey plot.
Canopy cover (CANC) Average canopy cover (%) measured at 4 cardinal directions
with convex densiometer. Estimates taken within two 11.4-m
Hardwood density (HDWD) Density (n/ha) of hardwood stems >22 cm dbh. Estimate from
two 11.4-m radius plots.
Pine density (PIND) Density (n/ha) of pine stems >22 cm dbh. Estimate from two
11.4-m radius plots.
White cedar density (CEDD) Density (n/ha) of white cedar stems >22 cm dbh. Estimate from
two 11.4-m radius plots.
Bald Cypress density (CYPD) Density (n/ha) of bald cypress stems >22 cm dbh. Estimate
from two 11.4-m radius plots.
Conifer density (COND) Density (n/ha) of conifer stems >22 cm dbh. Estimate from two
11.4-m radius plots.
340 Southeastern Naturalist Vol. 10, No. 2
the continued arrival or increased activity of D. v. waynei or the passage of D. v.
virens. Detections steadily declined throughout the month of May. This decline
may represent a diminution of singing on the part of breeding residents, the passage
of D. v. virens moving toward breeding locations to the north, or both.
Black-throated Green Warblers did not use survey plots of different habitat
types according to their availability (Fig. 3) (χ2 = 31.7, df = 5, P < 0.001). Birds
were detected less than expected within Pond Pine pocosin and hardwooddominated
plots and more than expected within plots with white cedar and Bald
Cypress. Occupied and unoccupied survey plots differed with respect to both
vegetation structure and canopy composition (Table 3). Occupied plots had signifi
cantly higher canopy cover (df = 119, F-statistic = 6.6, P = 0.011) and lower
understory density (df = 119, F-statistic = 7.8, P = 0.006). These two factors
are negatively correlated suggesting the obvious relationship that the shading of
higher canopy cover leads to a reduction in understory vegetation. The influence
of forest type on the distribution of breeding sites is suggested by the difference
between occupied and unoccupied survey plots in the amount of conifers in the
canopy. For example, the difference between occupied and unoccupied plots
in the density of large pines was nearly significant (df = 119, Mann-Whitney
U-statistic = 1452.5, P = 0.055). The difference in the density of large cedar
(df = 119, Mann-Whitney U-statistic = 1569.5, P = 0.045) and cypress (df = 119,
Mann-Whitney U-statistic = 1533.0, P = 0.032) stems in the canopy was signifi-
Figure 2. Seasonality of Black-throated Green Warbler detections. Dates indicate the
beginning of survey blocks. The same network of survey plots (n = 266) was surveyed
during each time block.
2011 B.D. Watts, B.J. Paxton, and F.M. Smith 341
cant. When pines, cedar, and cypress stems are combined, the resulting parameter
(COND) difference between occupied and unoccupied plots was highly signifi-
cant (df = 119, F-statistic = 13.8, P = 0.003).
Figure 3. Relative frequency of Black-throated Green Warbler detections by habitat type.
See Table 1 for sample sizes by habitat.
Table 3. Comparisons of vegetation parameters between occupied and unoccupied survey plots
(see Table 2 for parameter abbreviations). Statistics are F-values unless otherwise specified. Mean
values presented are individuals/ha.
Parameter (mean ± SE; n = 54) (mean ± SE; n = 67) Statistic P-value
UND 15,456.0 ± 896.60 19,820.0 ± 1201.80 7.8 0.006
SAPD 2025.0 ± 441.40 1409.0 ± 178.60 1.9 0.167
SUBD 732.9 ± 66.47 620.9 ± 48.32 1.9 0.166
CAND 192.7 ± 11.02 173.5 ± 8.01 2.1 0.152
CANH 17.2 ± 0.51 19.1 ± 0.55 6.0 0.016
CANC 84.3 ± 1.14 79.1 ± 1.58 6.6 0.011
HDWD 108.4 ± 13.11 105.4 ± 8.45 0.1 0.842
PIND 69.1 ± 10.01 43.0 ± 7.59 1452.5A 0.055
CEDD 28.0 ± 10.10 8.6 ± 4.40 1569.5A 0.045
CYPD 9.5 ± 3.05 2.7 ± 1.24 1533.0A 0.032
COND 106.7 ± 12.00 54.3 ± 8.16 13.8 0.003
AMann-Whitney U statistic.
342 Southeastern Naturalist Vol. 10, No. 2
The Wayne’s subspecies of the Black-throated Green Warbler currently breeds
from southeastern Virginia along the coast south to approximately Charleston,
SC. Throughout much of this range, the species breeds in very low densities.
An exception to this pattern is the Great Dismal Swamp, where the species was
reported to be a fairly common breeder from the 1950s through 1970s (Meanley
1977), and Dare County within the Albemarle-Pamlico peninsula, where high
breeding densities were recorded in the early 1980s (E.F. Potter, unpubl. data).
Results from this study support recent suggestions (B. Meanley and D. Schwab,
unpubl. data) that the population within the Great Dismal Swamp has declined.
Although the species does continue to breed within the Swamp, none of the 83
points surveyed were classified as breeding sites based on criteria developed
here. In contrast, the breeding population within the Alligator River NWR and
Dare Bombing Range was found to be similar to that reported in the early 1980s
(E.F. Potter, unpubl. data). This location may support one of the highest breeding
densities of any area within the subspecies range.
No Black-throated Green Warblers were detected within Pocosin Lakes
NWR. Nearly all of the survey plots established within the refuge were Pond
Pine pocosin habitat. This species is known to utilize this habitat within the
Albemarle-Pamlico peninsula (E.F. Potter, unpubl. data). In addition, the species
is documented to occur well west of the study area (Wilson and Watts 2000). It
is possible that the lack of use reflects the fragmented nature of these patches or
their condition (e.g., tree density, stand age).
Birds began to arrive within study areas during the first week of April. This
timing is consistent with other accounts that have listed arrival dates within
the southern portion of the breeding range in mid- to late March (Sprunt 1953,
Wayne 1910) and within the northern portion of the breeding range at the end of
March or early April (Meanley 1977). Detection rates increased throughout April
and then began to decline through May and into early June. This pattern is also
consistent with previous authors who stated that the species does not become
common within the region until mid- to late April (Meanley 1977, Sprunt 1953).
Singing rates have been suggested to diminish rapidly after chicks hatch, which
may partially account for the decline in detection rates through May. In support
of this, E.F. Potter (unpubl. data) stated “in late May and early June, full song
was rarely heard after 0900 EDT.”
The peak in birds in late April may represent the passage of the nominate subspecies
D. v. virens through the region. The timing of this peak would be consistent
with breeding times reported for populations to the north in New England. E.F.
Potter (unpubl. data) indicates that birds were detected in numerous locations in
mid-April in coastal North Carolina, where no birds were detected at later dates,
suggesting the presence of transients. Sprunt (1953) points to the dearth of records
of Black-throated Green within the extreme southeast in spring and suggests that
D. v. virens does not likely pass through the range of D. v. waynei. Dendroica v.
virens winters primarily within Central America between Mexico and Panama,
and most individuals apparently migrate north via a land route through Mexico and
Texas and continue on an inland track to the Appalachians and northern breeding
2011 B.D. Watts, B.J. Paxton, and F.M. Smith 343
areas (Stevenson 1957). However, Black-throated Green Warblers do winter
throughout the Caribbean and south Florida in low numbers (e.g., Emlen 1977,
Morse 1993). Dendroica v. waynei has been suggested to winter in western Cuba
(AOU 1957). The taxonomic origin of other populations that winter in the Caribbean
has not been clearly documented. Confusion remains about the level and
timing of overlap between these subspecies. For example, does D. v. virens winter
within the Caribbean? Are D. v. virens and D. v. waynei geographically isolated
on the winter grounds? What is the geographic range of D. v. waynei on the winter
grounds? Because D. v. waynei is a small, unique population that is geographically
isolated on the breeding grounds, understanding the risks that it faces within the
winter range has conservation significance.
Black-throated Green Warblers occurred across the full gradient of habitat
types from hardwood-dominated sites to sites supporting a Bald Cypress component.
However, birds were not detected with the same frequency across all habitat
types. Within this gradient, there was a lower frequency of occurrence within
hardwood-dominated sites. In addition, survey plots classified as breeding sites
had significantly higher densities of conifers including Loblolly Pine, Atlantic
White Cedar, and Bald Cypress. These results are consistent with impressions
expressed by other observers. In South Carolina, Wayne’s Warblers are suggested
to be associated with non-alluvial patches of Bald Cypress (Curson et al. 1994,
Sprunt 1953). E.F. Potter (unpubl. data) indicates that a common trait among territories
that she observed in coastal North Carolina was the presence of pines and
or Bald Cypress. She emphasizes the occurrence of mature trees, a characteristic
that is common to other accounts (Sprunt 1953).
The unique complex of habitats within the outer coastal plain from southeastern
Virginia through the Carolinas supports a number of unique avian forms. Like the
Wayne’s Black-throated Green Warbler, these forms include endemic subspecies
and disjunct populations. For example, an isolated population of Dendroica cerulea
Gmelin (Cerulean Warblers) occurs along the lower Roanoke River and Chowan
Basin (Lynch 1981). A distinct form of Dendroica discolor Vieillot (Prairie Warbler)
that breeds within tall pocosin and forested habitats occurs in coastal Virginia and
North Carolina (Meanley 1977, Nolan et al. 1999). An unusually dense population
of Helmitheros vermivorum (Gmelin) (Worm-eating Warbler) breeds in flat pine
plantations and pocosins compared to steep, hardwood slopes elsewhere in the species’
range (Watts and Wilson 2005). Vermivora bachmanii Audubon (Bachman’s
Warbler) has been suggested to have a close association with Arundinaria gigantea
Walter (Cane) thickets within the region (Remsen 1986). Virtually all of these forms
appear to winter exclusively in the Caribbean. As with other species of conservation
concern, populations that winter exclusively on small isolated islands are subject
to dramatic declines if land-use changes are not in their favor. From a conservation
perspective, it is important to determine the risks that the Wayne’s form of the Blackthroated
Green Warbler faces on both the breeding and winter grounds.
We thank Chuck Hunter, Bob Noffsinger, and Keith Watson for the opportunity to
conduct this study. Dennis Stewart, Wendy Stanton, Cynthia Britton, Teresa Cherry, and
344 Southeastern Naturalist Vol. 10, No. 2
Dennis Helms provided insight into potential field sites and logistical support within
study areas. We appreciate the dedicated efforts of Sean Flint and William Sbrega in
conducting bird surveys and measuring vegetation under very difficult field conditions.
Lydia Whitaker, Carlton Adams, Renee Peace, Anne Womack, Gloria Sciole, Mark Roberts,
and Cheryl Pope provided administrative support. Financial support was provided
by the US Fish and Wildlife Service (Region 4) and the Center for Conservation Biology
at the College of William and Mary. We thank the editor and two anonymous reviewers
for helpful comments on an earlier draft of this manuscript.
American Ornithologists Union (AOU). 1957. The A.O.U. checklist of North American
birds. American Ornithologists Union, Lord Baltimore Press, Baltimore, MD.
Ashe, W.W. 1894. The forests, forest lands, and forest products of eastern North Carolina.
North Carolina Geological Survey Bulletin No. 5. Raleigh, NC.
Bangs, O. 1918. A new race of the Black-throated Green Wood Warbler. Proceedings of
the New England Zoological Club 6:93–94.
Curson, J., D. Quinn, and D. Beadle. 1994. Warblers of the Americas: An Identification
Guide. Houghton Mifflin Company, New York, NY.
Emlen, J.T. 1977. Land bird communities of Grand Bahama Island: The structure and
dynamics of an avifauna. Ornithological Monograph 24. American Ornithologists’
Union, Washington, DC.
Frost, C.C. 1987. Historical overview of Atlantic White Cedar in the Carolinas. Pp.
257–263, In A. D. Laderman (Ed.). Atlantic White Cedar Wetlands. Westview Press,
Lynch, J.M. 1981. Status of the Cerulean Warbler in the Roanoke River basin of North
Carolina. Chat 45:29–35.
Meanley, B. 1977. Birds of the Dismal Swamp, Virginia–North Carolina. Raven 48:3–25.
Morse, D.H. 1993. Black-throated Green Warbler (Dendroica virens). No. 55, In A. Poole
and F. Gill (Eds.). The Birds of North America. The Academy of Natural Sciences,
Philadelphia. PA, and The American Ornithologists’ Union, Washington, DC.
Nolan, V., Jr., E.D. Ketterson, and C.A. Buerkle. 1999. Prairie Warbler (Dendroica
discolor). No. 455, In A. Poole and F. Gill (Eds.). The Birds of North America. The
Academy of Natural Sciences, Philadelphia. PA, and The American Ornithologists’
Union, Washington, DC.
Oberholser, H.C. 1974. The Bird Life of Texas, Volume 2. University of Texas Press,
Remsen, J.V., Jr. 1986. Was Bachman’s Warbler a bamboo specialist? Auk 103:216–219.
Sprunt, A., Jr. 1953. Wayne’s Black-throated Green Warbler. US National Museum Bulletin
Stevenson, H.M. 1957. The relative magnitude of the trans-gulf and circum-gulf spring
migrations. Wilson Bulletin 69:39–77.
Watts, B.D., and M.D. Wilson. 2005. The use of pine plantations by Worm-eating Warblers
in coastal North Carolina. Southeastern Naturalist 4:177–187.
Wayne, A.T. 1910. Birds of South Carolina. Charleston Museum of Natural History.
Wilson, M.D., and B.D. Watts. 2000. Breeding-bird communities of the Parker Tract
Hardwood Forest Swamps. Center for Conservation Biology Technical Report, CCBTR-
00-04. College of William and Mary, Williamsburg, VA. 49 pp.