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2009 SOUTHEASTERN NATURALIST 8(3):547–552
Notes on Breeding Sharp-shinned Hawks and Cooper’s
Hawks in Barnwell County, South Carolina
Mark Vukovich1,* and John C. Kilgo1
Abstract - Breeding records of Accipiter striatus (Sharp-shinned Hawks) in the
southeastern US are scattered and isolated. We documented a Sharp-shinned Hawk
and Accipiter cooperii (Cooper’s Hawk) nest while conducting a telemetry study on
Melanerpes erythrocephalus (Red-headed Woodpeckers) in Barnwell County, SC in
2006 and 2007. We report the first known nest of a Sharp-shinned Hawk in Barnwell
County, SC and the first report of Sharp-shinned Hawks preying upon Red-headed
Woodpeckers. Thirteen of 93 (13.9 %) woodpeckers were killed by accipiters in the
summers of 2006 and 2007. Large, contiguous forests managed for Picoides borealis
(Red-cockaded Woodpeckers) may be used by breeding Sharp-shinned Hawks. The
bright plumage, loud calls, and behavior of Red-headed Woodpeckers, particularly
during the nestling stage, may make them conspicuous prey for accipiters.
Accipiter striatus Vieillot (Sharp-shinned Hawk) and Accipiter cooperii
(Bonaparte) (Cooper’s Hawk) are year-round residents of the southeastern
US that typically prey upon small to medium-sized birds and mammals. In
North America, the core breeding range of Sharp-shinned Hawks includes
the contiguous boreal and mixed forests of Canada, the Appalachian mountains,
the northern Midwest, and the western and northern US (Bildstein
and Meyer 2000). Sharp-shinned Hawks regularly nest as far south as the
mountainous regions of the Carolinas and Georgia, but there are few modern
records of nests from the Piedmont and only one from the Coastal Plain
(Cely 2003, Davis 1998, Gobris 1994). Sharp-shinned Hawks, however,
are known to breed as far south as Central and South America (Bildstein
and Meyer 2000). Although Sharp-shinned Hawks are easily observed and
counted at migration sites in North America, they are among the most difficult raptors to detect during the breeding season because of their frequent
use of unbroken forest canopies (Reynolds and Wight 1978, Reynolds et al.
1982) and concealment of nests in upper tree canopies (Wiggers and Kritz
1991). Therefore, little is known about nesting activity at the perimeters
of their known breeding range where territories are scattered and isolated.
Cooper’s Hawks are more common than Sharp-shinned Hawks in the South
Atlantic Coastal Plain and Piedmont.
We documented several predation events on Melanerpes erythrocephalus
(L.) (Red-headed Woodpeckers) by Sharp-shinned and Cooper’s Hawks
while conducting research in South Carolina in 2006 and 2007. Radio
1 Southern Research Station, USDA Forest Service-Savannah River, New Ellenton,
SC 29809. *Corresponding author - firstname.lastname@example.org.
548 Southeastern Naturalist Vol. 8, No. 3
transmitters on the woodpeckers led us to the nests of the hawks, and locations
of the woodpecker territories allowed inference about home ranges of
these hawks. Here we present: 1) evidence of a breeding record for Sharpshinned
Hawk in South Carolina, 2) a brief summary of modern records
for Sharp-shinned Hawks for the southeastern US, and 3) the first report of
Sharp-shinned Hawks preying upon Red-headed Woodpeckers.
We studied Red-headed Woodpeckers from May to August 2006–2007
on the US Department of Energy’s Savannah River Site (SRS), an 80,000-
ha National Environmental Research Park in Aiken and Barnwell counties,
SC. The SRS is in the Upper Coastal Plain and Sandhills physiographic
provinces. Our woodpecker study sites included 50–60-yr old Pinus taeda
L. (Loblolly Pine) forests with scattered Quercus spp. (oaks) and Carya spp.
(hickories). The area surrounding these sites was similar but also contained
some younger pine plantations and old-growth bottomland hardwood forest
in riparian zones.
We captured Red-headed Woodpeckers at ground and sub-canopy levels
using mist nets, and at cavities using a telescoping pole with a net attached.
We attached a 1.9-g transmitter (Holohil Systems, Ltd.) on the backs of
woodpeckers using the harness design of Nesbitt et al. (1982), but modified
to exclude the breast band. To ensure stability and limit movement of the
transmitter, we used crimping beads at each tube opening of the transmitter.
We used a standard size for all harnesses. The transmitter harness package
weighed 2.1 g (2.6–3.6% of body mass), and the battery life of transmitters
was 16 weeks. The behavior of Red-headed Woodpeckers was not affected
by the harness (M. Vukovich and J.C. Kilgo unpubl. data). We used receivers
with an H-antenna or 3-element Yagi antenna (Telonics, Inc.; Advanced
Telemetry Systems, Inc.) to relocate woodpeckers by homing 4 to 5 times per
week. We marked woodpecker locations with a handheld GPS unit. When
a radio signal was not detected from a bird’s known territory, we searched
surrounding areas in expanding concentric circles until contact was made.
We tracked 93 Red-headed Woodpeckers (n = 46 in 2006, n = 47 in 2007), of
which 13 were killed by accipiters (n = 7 in 2006, n = 6 in 2007). Most predation
events occurred in July (77%). In 2006, an average of 15 days was needed to relocate
missing birds. In 2007, an average of 1 day was needed to relocate birds.
The following are descriptions of significant depredation events.
Sharp-shinned Hawk depredations
On July 17, 2006, 3 days after the last contact with Red-headed Woodpecker
no. 77, we discovered its radio signal 2.3 km north of its last
known location. On approaching the signal, we heard an alarm call of a
Sharp-shinned Hawk and briefl y observed it fl ying around us. We found
2009 M. Vukovich and J.C. Kilgo 549
the transmitter and remains of 77 on the ground. We observed old prey remains
and feathers of other small passerines in the immediate area while we
searched briefl y but unsuccessfully for a nest.
On July 3, 2007, we located the signal of bird 101 in a Pinus palustris
Miller (Longleaf Pine) 2.1 km north of 101’s last known location, and about
2.8 km east of the recovery of bird 77 in 2006. Upon approach, we heard
an alarm call of an adult Sharp-shinned Hawk. An adult female hawk approached
within 5 to 10 m of us while circling, diving, and continuing to give
alarm calls. Although we heard begging calls of Sharp-shinned Hawk fl edglings
on at least 2 occasions and we observed several old nests consistent
with the size of small accipiters, we did not find a definitive Sharp-shinned
Hawk nest. Observations of fl edglings were only fl eeting glimpses. Two additional
woodpecker depredations in 2007 (birds 107 and 116) led us to the
same area, with 1 transmitter located in a Longleaf Pine and the other on the
ground. The transmitters of bird 107 and 116 were approximately 3.0 and 1.8
km from their last known locations.
On July 9, 2007, we discovered a nest when we observed an adult female
Sharp-shinned Hawk carrying unknown prey land in the top of a Longleaf
Pine. She then quickly left with the prey and fl ew to fl edglings begging
nearby. The nest was concealed near the top of the Longleaf Pine (23.5 m) in
which she had first landed. The tree’s height was approximately 24.4 m and
diameter at breast height (dbh) was 40.6 cm. The nest tree was approximately
42 m from the tree that contained the transmitter of bird 101. Whitewash and
small passerine remains were scattered about the base of the nest tree. No
nestlings were seen or heard in the nest. The surrounding habitat was dominated
by 50- to 60-year-old Longleaf Pines that were moderately thinned.
The area had been burned (prescribed fire) the preceding winter and there
was little to no midstory or understory.
On July 13, 2007, we located the signal of the transmitter for bird 103
in a tree 0.9 km from its last known location and approximately 1.4 km
southeast of the Sharp-shinned Hawk’s nest. A hatch-year Sharp-shinned
Hawk circled and called in alarm. We found no remains of 103 at the time,
but on 26 July, we found the transmitter and Red-headed Woodpecker
feathers on the ground under the tree.
Cooper’s Hawk depredations
On July 25, 2006, we fl ushed a hatch-year Cooper’s Hawk on the ground
20 m from the remains of bird 52 in a riparian zone about 0.6 km west of its
territory. The location was under the same large Liriodendron tulipifera L.
(Tulip Poplar) where the remains of birds 46, 53, 59, 73, and 81 had been
found. Average distances of these 4 birds from their last locations were 1.6
km (range = 1.1–2.1 km). Other prey remains present included feathers of
Cyanocitta cristata (L.) (Blue Jay) and Colaptes auratus (L.) (Northern
Flicker). We found no nest in subsequent searches, but observed 2 old,
medium-sized stick nests in the area. We concluded that all nestlings fl edged
and that the Tulip Poplar was used as a perch for plucking prey by adult and
hatch-year Cooper’s Hawks.
550 Southeastern Naturalist Vol. 8, No. 3
On June 18, 2007, we located the signal for bird 108 in the same riparian
zone, 101 m from the Tulip Popular perch used for plucking in 2006. The
transmitter and some remains of bird 108 were approximately 1.8 km from
its last known location. We heard an alarm call of an adult Cooper’s Hawk
upon approach and then observed a nest with 2 large nestlings (18–30 days)
23.5 m high in a Liquidambar styracifl ua L. (Sweet Gum). The tree’s height
was approximately 35 m and dbh was 38.9 cm. An examination of the area
directly under the nest revealed whitewash, Blue Jay feathers, and smallmammal
remains. The tree was within 20 m of a small creek and surrounded
by mixed pines and hardwoods. The area had mixed ages of trees (10–90
years old) with a dense midstory and moderate understory. On July 3, 2007,
we located the remains of bird 110 on the ground 10 m from the nest tree and
approximately 0.9 km from its last known location.
We confirmed nesting by Sharp-shinned Hawks in 2007, but the species
was present in the area in 2006 and may have been nesting then. Despite
extensive long-term ornithological fieldwork at SRS, Sharp-shinned Hawks
have never been documented as a breeding species (Kilgo and Bryan 2005).
Possible nests of Sharp-shinned Hawks have been reported within 50 km of
our study site by the South Carolina Breeding Bird Atlas (Fig. 1; Cely 2003).
Only 10 Sharp-shinned Hawk nests have been reported from South Carolina
Figure 1. Counties in South Carolina and Georgia with confirmed (dark gray), and
possible/probable (light gray) breeding Sharp-shinned Hawks since 1988 (taken
from South Carolina and Georgia Breeding Bird Atlases). Barnwell County, SC, is
indicated with a black dot.
2009 M. Vukovich and J.C. Kilgo 551
and Georgia since 1988 (Fig. 1; Cely 2003; Gobris 1994; Georgia Breeding
Bird Atlas, Forsyth, GA, unpubl. data). Given the difficulty of detecting
and accurately identifying Sharp-shinned Hawks, combined with the species’
widely scattered distribution in the area, we suspect that nesting pairs
may have gone undetected. The existence of another pair of Sharp-shinned
Hawks near our study site remains uncertain but possible based on the extent
of suitable habitat and current management practices of the area. Large, contiguous
pine forests, particularly Picoides borealis (Vieillot) (Red-cockaded
Woodpecker) management areas, in the southern US may be used by breeding
The distance between the Sharp-shinned Hawk and the Cooper’s Hawk
nests was 3.9 km. Researchers have reported two Sharp-shinned Hawk nests
and a Cooper’s Hawk nest 300 m apart in Oregon (Reynolds and Wight
1978). They concluded that overlapping home ranges probably occurred
between the species. Based on the locations of territories of Red-headed
Woodpeckers depredated by accipiters, no overlap of accipiter home ranges
occurred in 2006, but some minimal overlap may have occurred in 2007.
Although Cooper’s Hawks have been known to prey on Red-headed
Woodpeckers (Errington 1933), this is the first report of Sharp-shinned
Hawks preying upon Red-headed Woodpeckers. The mean mass (±SE) of
woodpeckers depredated by accipiters in our study was 67.9 ± 1.4 g. Turdus
migratorius L. (American Robin), a frequent prey species of Sharp-shinned
Hawks (Storer 1986), is larger than a Red-headed Woodpecker, but both
species approach the upper limit of prey sizes for Sharp-shinned Hawks
(Bildstein and Meyer 2000). Overlap of prey niches for Cooper’s Hawks and
Sharp-shinned Hawks have been reported (Reynolds and Meslow 1984). The
female Sharp-shinned Hawk may have hunted more often in the latter stages
of nesting and specialized on woodpeckers (female accipiters are larger than
males). However, because we did not get good views of hunting accipiters
and because Cooper’s Hawks were present, we were not able to positively
identify hunting accipiters to sex.
Although the total number of woodpeckers killed was similar between
years, there were differences in the number taken by accipiters. During
2006, Cooper’s Hawks preyed on more radio-instrumented woodpeckers
(n = 6) than Sharp-shinned Hawks (n = 1), but the opposite was so during
2007, when 4 woodpeckers were taken by Sharp-shinned Hawks and 2 by
Cooper’s Hawks. We suspect that both accipiters shifted their territories and
hunting areas between years, perhaps caused by fl uctuations in numbers of
prey or by their annual differences in clutch sizes and survival of nestlings
or fl edglings.
Most predation events of Red-headed Woodpeckers by accipiters occurred
in July. July is typically when there are large numbers of nestlings or
fl edglings of Red-headed Woodpeckers at SRS (M. Vukovich, pers. observ.)
and it is also the late-nestling to fl edgling period of accipiters in the Carolinas
(Bildstein and Meyer 2000, Rosenfield and Bielefeldt 2006). The bright
552 Southeastern Naturalist Vol. 8, No. 3
plumage, loud calls, and behavior of Red-headed Woodpeckers, particularly
during the nestling stage, may make them a conspicuous prey species for
both accipiters. In addition, Red-headed Woodpeckers are the most abundant
breeding woodpecker on our study site (Lohr et al. 2002). This potential prey
base combined with the presence of extensive, contiguous mixed forest may
have been among the factors that made SRS attractive to accipiters.
We thank K. Legleu, K. Nayda, and K. Frier for outstanding work in the field
and J. Blake for logistical support. Funding for Red-headed Woodpecker research
was provided by the US Department of Energy - Savannah River Operations Office
through the USDA Forest Service Savannah River under Interagency Agreement No.
DE-AI09-00SR22188, and by the USDA Forest Service Southern Research Station.
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