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22001155 SOUTHEASTERN NATURALIST 1V4o(4l.) :1745,7 N–7o7. 04
Breeding Distribution and Population Persistence of
Loggerhead Shrikes in a Portion of the North Carolina
Douglas B. McNair*
Abstract - This study provides the first comparison of historical (1979–1994) and recent
(2012–2013) breeding distributions of Lanius ludovicianus (Loggerhead Shrike) at a single
location in southeastern North America. I conducted roadside and area searches for Loggerhead
Shrikes in the spring (April–early June 2012 and late March–early May 2013) in
Richmond County, NC, and small areas of 4 adjacent counties. Most of the study area is
within the Sandhills, a subregion of the Coastal Plain. I documented a total of 44–45 breeding
territories in 2012–2013, of which 36–38 (82–84%) were in the Sandhills, where I
estimated the recent breeding density to be 3.2–3.4 pairs/100 km2. In both years, a smaller
percentage of confirmed historic breeding sites were occupied in the Piedmont compared to
the Sandhills portion of the study area, and the Piedmont had a much lower breeding density
(0.6–0.8 pairs/100 km2). Sixteen of 22 (73%) confirmed historical breeding sites were
occupied (n = 10) or retained suitable breeding habitat (n = 6) for Loggerhead Shrikes in
2012–2013. The breeding population in the sampled portion of the Sandhills has apparently
declined slowly yet is still fairly stable, an unexpected result based on sharp declines of
Loggerhead Shrikes in the Atlantic Coastal Plain for over the past 40 years as documented
by coarse-scale surveys (breeding bird surveys, Christmas bird counts, spring bird counts).
This study reaffirms the importance of conducting fine-scale surveys to produce a precise
estimate of a persistent population in a geographically restric ted area.
The Sandhills is a subregion of rolling, sandy hills in the Inner Coastal Plain
of the Carolinas. They are ancient beach dunes that generally divide the Piedmont
from the Coastal Plain. Endangered and threatened avian species that occupy
managed mature Pinus palustris Mill. (Longleaf Pine) forest in the Sandhills,
such as Picoides borealis Vieillot (Red-cockaded Woodpecker) and Peucaea
aestivalis Lichtenstein (Bachman’s Sparrow) have received the bulk of research
attention (Brust et al. 2004; Carter et al. 1983; Kesler and Walters 2012; J. Marcus,
The Nature Conservancy, Southern Pines, NC, pers. comm.). Few other avian
species, other than gamebirds and recently Falco sparverius L. (American Kestrel;
Anchor and Brust 2004, Miller et al. 2012), have received attention despite
the importance of agricultural land that comprises slightly over 1/5 of the generally
forested area of Richmond County, NC. This agricultural land is especially rich
in landbirds, including migrant and wintering Pooecetes gramineus Gmelin (Vesper
Sparrow) and Lanius ludovicianus L. (Loggerhead Shrike), both of which are
listed as special-concern species in North Carolina (NCWRC 2008). Loggerhead
*35 Rowell Road, Wellfleet, MA 02667; email@example.com.
Manuscript Editor: Jason Davis
2015 Vol. 14, No. 4
Shrikes in North Carolina are considered permanent residents, perhaps supplemented
by small numbers of migrant birds during winter (LeGrand et al. 2011). In
South Carolina, abundance does not appear to vary between seasons, suggesting
that the area does not receive a large influx of wintering migrants (DeMent et al.
2008, Gawlik and Bildstein 1993).
Studies on the breeding distribution and ecology of Loggerhead Shrikes have
been conducted in many areas of North America (Brooks and Temple 1990, Michaels
and Cully 1998, Sauer et al. 1995, Yosef 1996) where Loggerhead Shrikes
have sharply declined for over the past 40 years based on breeding bird survey
(BBS), Christmas bird count (CBC), and spring bird count (SBC) data (Cade and
Woods 1997; Lowe and Butcher 1990; Morrison 1981; Sauer et al. 1995, 2011;
Westphal 2009; Yosef 1996). North Carolina now represents the northeastern limit
of the Loggerhead Shrike’s breeding range in the Atlantic coastal states of North
America, except for some increasingly isolated areas in Virginia and a few patches
further north. Recent BBS data show that this index of current (2006–2010) Loggerhead
Shrike abundance in North Carolina is greatest in the south-central Inner
Coastal Plain (1–3 birds/route; Sauer et al. 2011), which includes the Sandhills subregion.
These coarse-scale data generally agree with recent anecdotal assessments
(LeGrand 2011) and SBC data collected by the Carolina Bird Club (e.g., Westphal
2009) which suggest that Loggerhead Shrikes have sharply declined in the North
Carolina Piedmont, but that the population decline in the Coastal Plain may have
leveled off during the past decade or so, with an area of local concentration in
Southern Pines, Moore County, in the North Carolina Sandhills. Reproductive success
has generally been high in the southeastern US and some other areas (Gawlik
and Bildstein 1990; Luukkonen 1987; Yosef 1996, 2001; though see Collister and
Wilson 2007 for information on reduced breeding success), so declines have generally
been attributed to habitat loss through land-use changes, including agricultural
intensification (Gawlik and Bildstein 1990, Yosef 1996).
Gawlik and Bildstein (1990, 1993) studied Loggerhead Shrikes in the northcentral
Piedmont of South Carolina, ~120 km west of the North Carolina Sandhills,
but no studies in North Carolina have defined the precise breeding distribution and
status of Loggerhead Shrikes in any region, county, or other defined geographic unit
despite the legal status of this species and its importance as a bioindicator species of
healthy diverse agricultural landscapes and sensitivity to processes of agricultural
intensification (Gawlik and Bildstein 1990, Yosef 1996). Richmond County (adjacent
to Moore County) has had intensively managed agriculture—primarily cotton
farming—over a long period from the end of the American Civil War until the mid-
20th century. The human population of generally rural Richmond County, which lies
mainly in the Sandhills, has increased only slightly (0.6%) from 1980 to 2014 (2014
estimate = 45,733; 37 individuals/km2; US Census Bureau 2015), although the total
housing units (a better measure of urbanization; Brown et al. 2005) increased 22%
from 1980 to 2011 (US Census Bureau 2015). From 1978 to 2012, farm acreage
declined from 26,839 to 19,252 ha (reduction of 28%), with the mean size and
number of farms each decreasing ~15% (US Department of Agriculture 2015), yet
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all types of pastureland declined more steeply, from 4505 to 2294 ha (loss of 2111
ha; 49%). Other grass- or forb-dominated agricultural habitats in the form of idle
cropland, cropland used for cover crops, cropland used for soil improvement, and
lands in conservation reserve or conservation reserve enhancement programs also
declined from 2111 to 1567 ha (loss of 544 ha; 26%). All of these habitats are generally
favorable for Loggerhead Shrikes (Smith and Kruse 1992), yet pastureland
is the most important habitat component for shrikes in the Atlantic coastal states
of southeastern North America, especially during the breeding season, and the loss
of pasturelands is correlated with a sharp decline in indices of shrike abundance
(Gawlik and Bildstein 1993). Loggerhead Shrikes in Richmond County have most
often been reported in agricultural landscapes with some pasturelands centered
around large residential yards where pairs have nested in coniferous or deciduous
trees and shrubs.
Yosef (1996) and Tryjanowski et al. (2003) writing about the Loggerhead
Shrike and European shrikes, respectively, cautioned that it is difficult to compare
historical and current distributions because the number of observers and level of
effort expended to survey shrikes have increased dramatically. However, a careful
assessment of historical data within the current context can provide some measure
of change in Loggerhead Shrike breeding distribution and population persistence
in the agricultural landscape of a portion of the North Carolina Sandhills. Based on
conversion of agricultural land—including a decline in grass- or forb-dominated
habitats in Richmond County—to industrial forest-land uses since 1950 (Brown et
al. 2005; D.B. McNair, pers. observ.; US Department of Agriculture 2015), a limited
negative influence of increasing urbanization, a sharp decline of Loggerhead
Shrikes in the Piedmont compared to a less pronounced decline in the Coastal Plain
of the Carolinas, and historical data in Richmond County from 1979–1994 as a
population baseline (see results), I expected Loggerhead Shrikes in 2012–2013 to
be uncommon to locally fairly common in the Sandhills and rare to locally uncommon
in the Piedmont and near the Fall Line (contact zone of the Piedmont with
the Sandhills and Coastal Plain). I also expected Loggerhead Shrikes to be most
numerous in agricultural areas and less numerous in other land-use types including
more-natural habitats such as managed Longleaf Pine forest, even though pine
savannas constitute ancestral habitat for Loggerhead Shrikes in southeastern North
America (Cade and Woods 1997).
The study area was comprised of Richmond County, NC, and small areas of 4
adjacent counties (North Carolina: Anson, Montgomery, Scotland; South Carolina:
Marlboro) for a total of 1772 km2. Moving clockwise around Richmond County (Puetz
1990a), the study area in eastern Anson County extended from the South Carolina
line at County Road 1832 north to Morven, northeast along NC 145 to US 74, west
to Lilesville, north on County Road 1704, west on County Road 1634 to NC 109,
and north to the Great Pee Dee River at the Richmond County line. The survey area
2015 Vol. 14, No. 4
in extreme southeastern Montgomery County extended from the Richmond County
line along US 220 to County Road 1524, and east to Drowning Creek at the Moore
County line until the creek reaches the Richmond County line. The study area in
western Scotland County extended from Drowning Creek at the Moore County line
south and west along US 15/501, encompassing Camp MacKall Military Reservation
and crossing the Sandhills Gamelands, west along the southern boundary of the
gamelands to County Road 1346, south along 1346 and County Road 1001 to Laurel
Hill, west and south along County Roads 1152 and 1145 and NC 381 to Gibson, and
west along NC 79 to the Marlboro County line. In extreme northern and northwestern
Marlboro County (Puetz 1990b), the study area extended from the Scotland County
line at County Road 714; generally west along County Roads 166, 257, and 258 to
the Richmond County line; south along SC 177 and west along County Roads 280,
37, and 630; south along County Roads 113 and 97 to US 1; and south and west to
the Great Pee Dee River at the Chesterfield County line. The only location within
the study area in 2012–2013 (not during the historical period) where access was
completely restricted centered on barracks where basic training was conducted at
Camp MacKall Military Reservation. Access to most of the grounds outside Morrison
Correctional Institution in 2012–2013 was partially restricted; it housed adult
medium-security inmates (absent during the historical period).
The study area is dominated by the Sandhills subregion (1130.4 km2) of the
Coastal Plain, but also includes a small area of the Inner Coastal Plain (12.4 km2)
in northwestern Scotland County (centered on and near Gibson), and a larger area
of the Piedmont (628.9 km2) in northwestern Richmond and eastern Anson counties.
The Fall Line generally separates the Piedmont from the Coastal Plain, but
transitional zones between the Piedmont and the Sandhills and Coastal Plain are
commonly irregular and broad—as much as 5 km wide (US Department of Agriculture
1999). Within the study area, this contact zone especially occurs near the Great
Pee Dee River in southwestern Richmond, southeastern Anson, and northwestern
Marlboro counties, respectively. For this study, I considered this contact zone to be
areas along and near the Fall Line where reddish or reddish-tinted soils occur with
I collected anecdotal data on the breeding distribution and breeding status (e.g.,
confirmed breeding evidence) of Loggerhead Shrikes within the study area defined
above for the period 1979 to 1994 (parts of 13 years represented). I considered
Loggerhead Shrikes to have been at potential breeding sites if adult birds were
present from March to August; I also included records from February if I had direct
breeding evidence. I classified Loggerhead Shrike territories as confirmed breeding
sites if I detected nests or adults with recently fledged juveniles. I considered single
males and/or females or pairs that occupied a site in at least 2 y or for a minimum
of 20 d in 1 y to be on breeding territories. I treated all other sites as uncertain
breeding locations. I recorded the physiographic region, county, nearest town, and
precise site (e.g., section of county road) in which the breeding-season location
occurred. Using Google Earth 2015 (version 7.1.2), I examined aerial photographs
2015 Vol. 14, No. 4
from 1993 to 2013 and made repeated site visits to assess the potential suitability
of available habitat at confirmed historical breeding sites without documented presence
of Loggerhead Shrikes in 2012–2013. These data (1979–1994) are henceforth
called historical data.
Tryjanowski et al. (2003) emphasized that use of 3 different survey methods
could severely underestimate detection of shrike species in Poland compared to
their most sophisticated method, which included nest searches and color banding
that estimated precise shrike densities. Pasinelli et al. (2011), however, demonstrated
that a variety of shrike survey methods, even for less-well-studied populations
(e.g., Lübcke 2007 cited in Pasinelli et al. 2011), still had negligible sampling variance
and provided precise density estimates. Kéry and Schmidt (2008) estimated
detection probability of Lanius collurio L. (Red-backed Shrike) in 1-km quadrats
to be high, with 2.7 surveys per season yielding a 95% probability of detecting
this species, if present. Following Kéry and Schmidt (2008) and Pasinelli et al.
(2011), I used strict criteria in 2012–2013 to ensure that Loggerhead Shrike counts
would have a high level of detection and be precise. All Loggerhead Shrikes were
unmarked so I could not measure site fidelity, yet presence in the same breeding
locations between 2 divergent periods can provide information to help understand
the cues used by Loggerhead Shrikes for habitat and land use.
In 2012–2013, I conducted a systematic survey of Loggerhead Shrike breeding
distribution in the same study area, focusing on the Sandhills subregion where I
expected most shrikes to be present. I included all historical breeding locations in
my 2012–2013 surveys. Consistent coverage and effort was comprehensive in both
years, even though I deemphasized collection of direct breeding evidence because
of time constraints imposed by covering such a large area. I used roadside surveys
supplemented by area searches to reduce roadside-survey biases of under-detection
of shrikes. Loggerhead Shrikes are slightly larger yet similar to Lanius collurio L.
(Red-backed Shrikes), with males especially using conspicuous perches on exposed
parts of hedges, trees, and shrubs in their territories during the breeding season. In
the North Carolina Sandhills, overhead utility wires along roadsides (Gawlik and
Bildstein 1993), fences, and other artificial perch sites preferred by Loggerhead
Shrikes were numerous, and provided additional, conspicuous perch sites. I conducted
surveys along all primary (federal and state highways), secondary (paved
and traversable unpaved county and town roads), and accessible tertiary roads
(other traversable unpaved public roads and private roads) within the study area
that crossed potential Loggerhead Shrike breeding habitats. Except on the busiest
highways, I generally drove 30 km/h or less to locate birds, stopping frequently;
these surveys included frequent trips on private tertiary roads (e.g., on farms which
were generally accessible). I remained a minimum of 15 minutes at each potential
site on each visit. To increase detection rates, I walked all areas that could not be
reached by road to within 200 m of potential Loggerhead Shrike habitats. I mapped
all surveyed sites using GPS.
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In 2012, I surveyed Loggerhead Shrikes on 33 days from 7 April to 4 June, a
2-month period that extended from pair formation to fledging of first young and the
beginning of renesting attempts (D.B. McNair, unpubl. data; Yosef 1996). In 2013,
I surveyed for Loggerhead Shrikes on 29 days from 31 March to 2 May, a compressed
5-week period that avoided most renesting attempts. I classified territories
as occupied on the basis of breeding behavior as well as nest detection. However,
except for finding nests and adults with fledged young, the criteria for designating
an occupied breeding territory in 2012–2013 were very strict compared to the
historical period. I visited all historical breeding locations of Loggerhead Shrikes
a minimum of 4 times each over a minimum of 20 days during the peak-breeding
period to document whether shrikes still occurred at these historic sites. Using the
same methods, I also surveyed all other areas of potential habitat to determine if
Loggerhead Shrikes occupied “new” (i.e., previously unrecorded) breeding locations
in 2012–2013. Unless I found a nest or adults with fledged young, a minimum
of 3 registrations over a minimum of 20 days at each site were required to qualify as
an occupied shrike breeding territory. I classified Loggerhead Shrikes at locations
that did not meet these criteria as visitors, or uncertain breeders not on occupied
territories. Search effort during surveys in both years was almost identical (2012:
3510 miles, 199.5 h; 2013: 3490 miles, 200.5 h).
I recorded the dominant land-use type within a 500-m radius of a nest or center
of shrike activity for each Loggerhead Shrike location. Gawlik and Bildstein (1993)
correlated indices of Loggerhead Shrike abundance with the percentage of available
pastureland as the most important habitat component in the Piedmont of South
Carolina; they noted that this relationship has also been found to apply in many
other areas and in many states. Pastures were frequent components of the agricultural-
habitat matrix of many Loggerhead Shrike breeding territories in the North
Carolina Sandhills, and could also be a component of other land-use types. In this
exploratory effort, I simply categorized the dominant land-use type, irrespective of
whether or not the sites contained pastures or pasture-like components as part of the
I used chi-square tests to analyze and compare nominal data on the breeding
distribution of Loggerhead Shrikes among geographic regions between the 2 divergent
time periods. I computed a two-tailed t-test, assuming unequal variances, to
analyze differences in detection rates of Loggerhead Shrikes on breeding territories
between the 2 recent years based on the first detection of presence at each site in
2012–2013. I compared these results with those of Kéry and Schmidt (2008) for
Red-backed Shrikes. Finally, I used Mann-Whitney U-tests to examine data from
uncertain breeding-season territories or visitation sites in 2012–2013 to determine
the minimum length of stay (days) and the date of first occurrence at sites visited
in one or both years compared to sites visited in one year but used as breeding territories
or confirmed breeding sites in the alternative year. Statistical significance
was set at P = 0.05. Otherwise, I present descriptive statistics.
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I documented a total of 58 historical Loggerhead Shrike locations in the study
area—43 (74%) in the Sandhills, 14 (24%) in the Piedmont and along or near the
Fall Line, and 1 in the Inner Coastal Plain just below the Sandhills. Forty-one
(71%) of these 58 locations were in Richmond County, and 36 (88%) of those were
in the Sandhills.
Breeding territories. I documented breeding territories at 28 (48%) of 58 historical
locations in 2012–2013; 22 (38%) of the locations were confirmed breeding
sites (nests or recently fledged young; Fig. 1). Seven (32%) of the 22 confirmed
breeding locations occurred along or near the Fall Line, the other 15 (68%) were
in the Sandhills. Twelve of 22 (55%) confirmed historical breeding sites were not
used during 2012–2013, even though 6 of these 12 sites (50%) retained suitable
breeding habitat. In contrast, the remaining 10 confirmed historical breeding sites
(45%) were used recently (9 of 10 in both years; 1 in 2012 only). Two of the 7
confirmed historical breeding sites along or near the Fall Line (29%) were active in
2012–2013, whereas 8 of the 15 confirmed historical sites in the Sandhills (53%)
were active (χ2 = 0.39, df = 1, P > 0.05). Thus, a total of 16 of 22 (73%) confirmed
historical breeding sites were occupied or retained suitable breeding habitat for
Loggerhead Shrikes in 2012–2013. The loss of suitable breeding habitat at 6 confirmed
historical sites (27%) occurred in agricultural (4 sites) and non-agricultural
landscapes (2 sites).
Uncertain breeding-season territories. The remaining 30 (52%) historical locations
constituted uncertain breeding season territories or visi tation sites.
I documented a total of 67 Loggerhead Shrike locations in the study area in
2012–2013. Fifty-six (84%) locations were in the Sandhills, 8 (12%) were in the
Piedmont and along or near the Fall Line, and 3 (4%) were in the Inner Coastal
Plain just below the Sandhills (Fig. 1); 44 locations were used both years, whereas
9 of 53 (17%) and 14 of 58 (24%) locations were used only in 2012 and 2013,
respectively. Most birds occurred in 3 core areas centered on northeastern Richmond
County (Ellerbe–Norman), east-central Richmond County (Hoffman), and
southeastern Richmond County (south of Rockingham and Hamlet) into adjacent
Scotland County (to Gibson). Fifty-one (76%) of these 67 locations were in Richmond
County, and 48 (72%) were in the Sandhills. The proportion of locations in
the Sandhills compared to locations in the Piedmont (including along and near the
Fall Line) and the Inner Coastal Plain was not significantly different between the 2
survey periods (2012–2013 vs 1979–1994; χ2 = 1.1, df = 1, P > 0.05). In 2012–
2013, 22 (33%) Loggerhead Shrike locations were used during both time periods
(17 of 51 in Richmond County; 33%).
Breeding territories. Forty-five (85%) of 53 and 44 of 58 (76%) Loggerhead
Shrike locations in 2012 and 2013, respectively, represented birds on breeding
territories; 32 of 57 (56%) breeding territories were used both years, whereas 13
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Figure 1. Location of 22 historical (1979–1994) confirmed breeding sites and 67 recent
(2012–2013) breeding-season locations of the Loggerhead Shrike in Richmond County, NC
(and small areas of 4 adjacent counties). Large, open circles refer to historical confirmed
breeding sites; small, filled squares represent 19 recent confirmed breeding sites in 1 or both
years; filled diamonds show 38 other recent breeding territories in 1 or both years, excluding
confirmed breeding sites, and filled Xs indicate 10 recent uncertain breeding-season
territories or visitation sites in 1 or both years, excluding confirmed breeding sites and other
recent breeding territories.
2015 Vol. 14, No. 4
and 12 breeding territories were used only in 2012 and 2013, respectively. I confirmed
breeding at a total of 19 (33%) of these 57 territories (Fig. 1), of which 15
(26%) were in Richmond County. During the 2012–2013 survey period for the
44–45 breeding territories, the estimated Loggerhead Shrike population density
in the study area was 2.5 pairs/100 km2. Loggerhead Shrike density was 0.6–0.8
pairs/100 km2 and 3.2–3.4 pairs/100 km2 for the Piedmont/Fall Line area and the
Loggerhead Shrikes on breeding territories were first detected during my initial
surveys at 40 of the 45 shrike locations (89%) in 2012 and at 41 of 44 locations (93%)
in 2013; shrikes were first detected during the 4th visit of surveys at the 5 remaining
breeding territories in 2012 and twice during the 2nd visit and once during the 3rd visit
at the 3 remaining breeding territories in 2013. Three of the 5 latter sites in 2012 were
also historical sites (1 was also used in 2013); one of these had partially restricted
access in 2012 (Morrison Correctional Institution). The mean detection rate for
1st detection of presence was slightly higher (more efficient) in 2013 compared to
2012, but the difference was not significant (2013: 1.09 visits ± 0.05 SE, 95% CI =
0.98–1.20, n = 44; 2012: 1.33 visits ± 0.14 SE, 95% CI = 1.05–1.61, n = 45; t = 1.59,
P = 0.12). I detected 5 (9%), 42 (74%), and 10 (18%) Loggerhead Shrike breeding
territories along primary, secondary, and tertiary roads (including supplemental areasearches
that departed from these roads), respectively.
Thirty-nine (68%) of the 57 Loggerhead Shrike pairs on breeding territories in
2012–2013 were within the agricultural land-use type. The number of breeding territories
in other land-use types occupied were as follows: 6 (11%) in rural housing
developments, 3 in industrial parks, 2 at raceways (in mowed grassy parking areas
and open Longleaf Pine forest), 1 at an airport, 1 at a prison, 1 in a cemetery, 1 on
a power-line right-of-way, 1 in a forest clearcut, 1 in a young pine plantation, and 1
in a managed mature Longleaf Pine forest (Gamelands Field-trial Grounds). Sand
pits and military drop-zones were not used as established breeding territories during
2012–2013 but had been used once each during the historical period.
Uncertain breeding-season territories. I classified a total of 19 sites as uncertain
Loggerhead Shrike breeding-season territories or visitation sites in 1 or both years.
Ten of 19 sites (53%) were only used as uncertain breeding-season territories, with
3 sites visited both years, 2 sites visited only in 2012, and 5 sites visited only in
2013 (= visitor only group). In contrast, 9 of 19 (47%) sites were used as uncertain
breeding-season territories in 1 year (3 sites in 2012, 6 sites in 2013), but were also
used as confirmed breeding sites (n = 1) or breeding-season territories (n = 8) in the
alternative year (= alternative group). Differences in the median length of stay and
date of first occurrence between these 2 groups were not significant (length of stay:
visitor only group = 1 day, alternative group = 14 days, Mann-Whitney U = 30;
date of first occurrence: visitor only group = 26 April, alternative group = 7 April,
Mann-Whitney U = 82.5; critical value of Mann-Whitney U-test = 28). However,
visiting Loggerhead Shrikes had a minimum stay of 13 days longer and arrived 17
days earlier at sites that had confirmed breeding or were used as breeding-season
territories in the alternative year—either 2012 or 2013.
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Three of the 4 longest stays at the 10 sites that Loggerhead Shrikes visited only
in 2012–2013 occurred at all 3 sites that were visited both years. This total included
1 historical site where breeding had been confirmed in managed Longleaf Pine forest
with pastures at the North Carolina Gamelands Field-trial Grounds headquarters
in 1988–1989 and 1993. Shrikes remained at this site for a minimum of 6 and 1
days, respectively, in 2012 and 2013 even though macrohabitat and land-use had
apparently remained unchanged (examination of aerial photos from 1993 to 2013 on
Google Earth [version 7.1.2], and D.B. McNair, pers. observ.). Similarly, there was
a Loggerhead Shrike breeding territory in 1981 and 1983–1984 at another historical
site nearby in Derby, Richmond County. In 2012, a pair was present at this site in
the same hedgerow among a similar matrix of agricultural habitats for a minimum
of 17 days but departed shortly after mechanized agricultural-management activities
occurred within their core territory; a pair remained on their breeding territory
here in 2013. Two confirmed historical breeding sites in a matrix of agricultural
habitats and pine forest in 1989–1990 at Scholl, along or near the Richmond–Scotland
county line, were used as visitation sites in 1 recent year, but used as breeding
territories in the alternative year in 2012–2013. Finally, a Loggerhead Shrike pair
abandoned a young pine plantation after 1 day in 2012 when 1 territorial adult Accipiter
cooperii Bonaparte (Cooper’s Hawk) unsuccessfully attempted to capture a
shrike; shrikes were not detected at this site in 2013.
My study is the first in the Carolinas or the rest of southeastern North America
that has re-assessed the breeding distribution of Loggerhead Shrikes between 2
different time periods. In contrast, many studies of shrike species in Europe have
documented their fine-scale breeding distribution and status over many years
(Kuczyński et al. 2010, Pasinelli et al. 2011), including records of increasing
and declining populations. My survey protocol in 2012–2013 did not allow me
to estimate any detection probability function, but my mean survey time for first
detection of presence with a 95% confidence interval was 1.09–1.33 visits, more
efficient than 2.7 visits on surveys for the Red-backed Shrike (Kéry and Schmidt
2008), although the latter species is probably less visible compared to the Loggerhead
Shrike. My protocol allocated 3 Loggerhead Shrike locations to the
uncertain breeding-season territory category in 2012, and 2 in 2013, even though
these sites had been used as confirmed historical breeding sites by shrikes and
still retained suitable breeding habitat. My protocol may have been too strict, but
I wanted to ensure that Loggerhead Shrike locations that were legitimate breeding
territories in 2012–2013 were rigorously documented and that my population
estimate was precise. I detected shrikes efficiently along primary and secondary
roads that traversed the Gamelands, but my detection rate may have been lower
along tertiary roads in managed Longleaf Pine forests where anthropogenic perch
sites are generally scarce. Most Loggerhead Shrike detections along tertiary roads
from 2004–2012 were concentrated at the Field-trial Grounds where managed
2015 Vol. 14, No. 4
fields and open Longleaf Pine stands are maintained (J. Marcus et al., unpubl.
data), which I covered in 2012–2013.
I under-recorded the number of Loggerhead Shrike breeding territories, but not
locations per se, during the historical period because of insufficient effort. Nonetheless,
Loggerhead Shrikes declined along or near the Fall Line where 5 confirmed
historical breeding sites were not used in 2012 (71% reduction), which is consistent
with a sharp decline reported for the Piedmont of North Carolina where the species
is now rare or locally very uncommon (LeGrand et al. 2011, Sauer et al. 2011).
The Loggerhead Shrike breeding population in my study area within the North
Carolina Sandhills was concentrated in 3 areas, but has slowly declined over approximately
the last 30 years despite a substantial loss of all types of pasturelands
as well as other types of grassy or forb-dominated habitats. This slowly declining
yet fairly stable population in the Sandhills is not predicted by CBC or BBS data
from North Carolina (Sauer et al. 1995, 2011), demonstrating the value of using
a strict survey protocol at a fine scale to produce a precise population estimate of
a resident species still occupying favorable land-use types and macrohabitats in a
geographically restricted area. In southern Indiana, where breeding populations of
migratory Loggerhead Shrikes restricted to 2 physiographic regions have sharply
declined (Burton and Whitehead 2002), a core population declined less (reduction
of 13%) than other populations (reduction of 60%) from 1988 to 2000. The breeding
population of Loggerhead Shrikes in my study area in the Sandhills probably
constitutes a core population, declining less precipitously compared to most other
areas in North Carolina.
Nonetheless, the breeding density of Loggerhead Shrikes in the North Carolina
Sandhills appeared to be low in 2012–2013 although few comparisons are available
in North America (cf., Yosef 1996, where roadside survey densities are actually indices
of abundance). All but 2 territorial pairs in the North Carolina Sandhills were
separated by a minimum distance of 1000 m, so any potential confusion of pair
identity that could occur in dense populations of unmarked Loggerhead Shrikes
rarely occurred. Behavioral observations pinpointed core-activity areas for pairs
that occurred close together, including probable nests in trees in rural farmyards
that I did not access because of privacy concerns.
Despite a low population density, population persistence (not site fidelity per se)
at breeding territories in 2012–2013 compared to historical data was approximately
33%. Considering that the 2 time periods were separated by 18–19 years, population
persistence appears to be high in my study area. The recent annual measure of
population persistence between 2012 and 2013 was 56%, and longer length-of-stay
and earlier arrival of Loggerhead Shrikes at territories used in alternative years and
reuse of some historical sites suggests population persistence between both recent
years may even have been higher. Annual re-occupancy of breeding territories of
continental Loggerhead Shrike populations has ranged from 41% to 73%, including
60% in Virginia (Luukkonen 1987, Yosef 1996). Takagi (2003) and Tryjanowski et
al. (2007) suggested that high site-fidelity of migratory Lanius cristatus L. (Brown
Shrike) in Japan and the Red-backed Shrike in Western Europe, respectively, was
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due to the patchy, isolated character of breeding habitats in intensive agricultural
landscapes that inhibited shrike dispersal. High site-fidelity in my study area within
the North Carolina Sandhills, coupled with local dispersal of unattached shrikes,
suggests that breeding territories are saturated.
I thank C.J. Randel for preparing Figure 1; J.A. Collazo, J. Ma rcus, and P. Tryjanowski
for their reviews of a penultimate version of the manuscript; and 2 anonymous individuals
for their reviews of the submitted version of the manuscript.
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