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Cliff Swallow Breeding Range Expansion along the Great Pee Dee River Corridor in the Carolinas
Douglas B. McNair

Southeastern Naturalist, Volume 12, Issue 3 (2013): 500–513

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D.B. McNair 2013 Southeastern Naturalist Vol. 12, No. 3 500 2013 SOUTHEASTERN NATURALIST 12(3):500–513 Cliff Swallow Breeding Range Expansion along the Great Pee Dee River Corridor in the Carolinas Douglas B. McNair* Abstract - Petrochelidon pyrrhonota (Cliff Swallow) initially expanded its breeding range to the Great Pee Dee River corridor of the Carolinas in the early 1980s. In 2012, I documented approximately 1700 active nests of the Cliff Swallow at 20 colony sites in the Lower Piedmont of North Carolina and Coastal Plain of South Carolina along this river corridor. Cliff Swallows nested primarily at bridges and other water-based sites but also bred at several land-based sites, including the first colony documented at a highway overpass in the Carolinas. Compared to colony sizes in the early 1980s and mid-1990s at 3 major sites in North Carolina, numbers in 2012 were approximately 1500% and 400% higher, respectively. Before this study, Cliff Swallows nesting along the Great Pee Dee River was documented only as far as Cheraw, at the Fall Line. This study demonstrates that breeding now occurs 145 km farther south along this corridor at 6 sites, including 2 sites in the tidewater region of South Carolina. Several bridges along this corridor with favorable structural characteristics for breeding are still unoccupied. The breeding range expansion front of interior populations along and near the Great Pee Dee River has moved slowly (≈3.25 km/yr), in an apparently stepwise manner. However, the gap between expanding interior and coastal populations is confounding the pattern of range expansion in the Lower Coastal Plain of South Carolina. Introduction Species’ range margins are typically characterized by specialized populations that occupy highly fragmented habitat and select for low rates of dispersal, regardless of theoretical considerations (Duckworth 2008, Simmons and Thomas 2004). Ecological factors are dominant in explanations of avian range expansions in southeastern North America (Fujisaki et al. 2010, Veech et al. 2011), including changes in habitat such as the creation of anthropogenic nest sites which accompany human settlement. This model fits the south- and east-ward breeding range expansion of 3 species of swallows in southeastern North America over the past 25 to 50 years over land and especially over water (Tachycineta bicolor Vieillot [Tree Swallow]: Cooper and Markham 1994, Lee 1993, Monroe et al. 2008, Shutler et al. 2012, Wagner et al. 2002; Hirundo rustica L. [Barn Swallow]: Brown and Brown 1999, McNair and Post 1993, Post and Gauthreaux 1989; and Petrochelidon pyrrhonota Vieillot [Cliff Swallow]: Brown and Brown 1995, Grant and Quay 1977, LeGrand et al. 2011, Lewis and McNair 1998, Post and Gauthreaux 1989, Sauer et al. 2011). The breeding range expansion of Cliff Swallows in the Carolinas has been attributed to patchy yet stable water-based anthropogenic changes, especially nest site availability at large bridges over reservoirs and lakes created by impounded waters; the first documented breeding record in the Carolinas occurred in the Upper Piedmont at Lake Hartwell, SC in 1967 (McConnell *35 Rowell Road, Wellfleet, MA 02667; dbmcnair@gmail.com. 501 D.B. McNair 2013 Southeastern Naturalist Vol. 12, No. 3 1981, Post and Gauthreaux 1989). Subsequently, the breeding range expansion has continued to rely primarily on water-based nest sites—large bridges or other large anthropogenic structures placed directly over water such as the faces of power stations (Southern 2010). However, a few land-based breeding sites away from water have recently been used in the Carolinas—at buildings (since 2007 in North Carolina: Davis 2007; since 2010 in South Carolina: Southern 2010), but not at highway overpasses (LeGrand et al. 2011), which were frequently used in western North America, especially in the central Great Plains as the species expanded eastward (Brown and Brown 1995). Regardless, the breeding range expansion of the Cliff Swallow in the Carolinas has been primarily driven by water-based anthropogenic structures. Land-based sites have only served a minor role despite their abundance, even in the Piedmont away from water where mud is readily available. Aside from some disjunct coastal and near-coastal breeding sites in the Carolinas over the past decade (Cely 2003, Davis 2002, LeGrand et al. 2011; but see Post and Gauthreaux 1989 for information on one earlier site in coastal South Carolina), the available evidence suggests the dispersal route of breeding Cliff Swallows has consisted primarily of a network of interconnected systems of major riverine corridors, especially in the Piedmont (Cely 2003, LeGrand et al. 2011, Post and Gauthreaux 1989, Sauer et al. 2011). One of the major breeding range expansion corridors in the Piedmont has been along the Yadkin- Pee Dee River system (LeGrand et al. 2011), as far southeast as Anson and Richmond counties, NC (LeGrand et al. 2011), and to the Fall Line at nearby Cheraw, SC (Cely 2003). Breeding along the Yadkin River occurred at High Rock Dam in Rowan and Davidson counties in the mid-1970s (LeGrand 1976, 1977), then farther south at Falls Dam in Stanley and Montgomery counties for the first time in 1977 (LeGrand 1977). Breeding along the range expansion front of the Great Pee Dee River (GPDR) corridor was first documented in the Lower Piedmont in 1981, when nesting Cliff Swallows were observed at the US 74 bridge over the GPDR at the Richmond County and Anson County line. Subsequent documentation of breeding along the GPDR corridor in the Lower Piedmont at the range expansion front has been limited to several sites along the GPDR, most recently (2010) at the water-based face of the power station beside Blewett Falls Dam in Anson County (Southern 2010). Blewett Falls Lake in the Lower Piedmont of NC is the last major water body along the GPDR until it reaches the coast of SC, over 160 km away. No land-based breeding sites along the GPDR corridor have been documented. In this study, I examine the current (2012) breeding distribution of Cliff Swallows along the GPDR corridor in the Carolinas, the first time the influence of a limited and patchy, yet stable anthropogenic nest-site resource along a defined range expansion front has been closely examined for any species of swallow in southeastern North America. I document water- and land-based anthropogenic colony sites in a corridor along and near the GPDR. The distribution of colony sites along the GPDR corridor is expected to be linear, with limited radial D.B. McNair 2013 Southeastern Naturalist Vol. 12, No. 3 502 distributions (cf., Tennessee; Coffey 1980). The main channel of the GPDR does not widen downstream except on the coast, so most bridge lengths at different crossings over the river are approximately the same. I hypothesize that range expansion will be slow and that colony-site population size, both water- and land-based, will decrease with increasing distance from the GPDR and will also decrease with decreasing distance toward the range expansion front. Cliff Swallows typically nest in large colonies (Brown and Brown 1995) and the largest colonies are expected to be at the largest bridges with the greatest lengths over the GPDR, at sites most distant from the range expansion front. Methods Cliff Swallow surveys I examined all water- and land-based structures with site characteristics (large structures with a vertical face and horizontal overhang for nest attachment at the 90º juncture; see Brown and Brown 1995) that had the potential to attract nesting Cliff Swallows along and near the GPDR from Richmond County, NC and adjacent areas south to the coast of South Carolina. The corridor was comprised of all accessible areas, including tributaries within 15 km of the river. This area includes all 10 bridges (with the exception of the US 95 bridge in South Carolina that I could not access) and one power station located over or along the GPDR, and numerous large structures, such as industrial buildings, located near the river. Colony sites were visited once or twice from mid-April through May 2012, at or near the peak of the breeding season for this single-brooded species (Brown and Brown 1995). Colony size was determined by counting the number of active nests at each site; the number of active nests was determined each visit by counting the number of complete nests as well as incomplete nests where adults were seen nest-building. In December 2012 and January 2013, I also resampled the same survey area, including all colony sites found in spring 2012 as well as any potential colony sites that may have been overlooked. Nest counts of complete or nearly complete nests (allowing for some degradation) during the following winter provide additional information on the total number of nests built at some sites (though not on the number of nests that were simultaneously active). I defined the distance of colony sites over or along the GPDR from this river as zero. The distance for other colony sites located away from this river was calculated using Google Earth 2012 (version 6.2.2) as the shortest direct-line distance from the river along the course of the water bodies to each of these colony sites, or in the case of the land-based colony sites, the shortest direct-line distance over land to the river. I also measured bridge length using Google Earth 2012. Historical data I obtained historical nesting data (1981–2011) for the study area from the Carolina Bird Club (CBC) database (extracted from The Chat, the CBC quarterly publication), and data before 1981 directly from The Chat and other published and unpublished sources. Although I examined unpublished sources including 503 D.B. McNair 2013 Southeastern Naturalist Vol. 12, No. 3 Animal Diversity Web (2012), the Carolinas Birding List at Birding on the Net (2012), Cornell Lab of Ornithology (2012a, b), Red Shank Software (2012), and Carolina Birds at Virtual Birder (2012), historical breeding information obtained from The Chat provided the most useful information in this study. Results 2012 data I documented 20 Cliff Swallow colony sites along the GPDR corridor in the Lower Piedmont and Coastal Plain of the Carolinas, with half of these colony sites in Richmond County, NC (Fig. 1, Appendix 1); only four of the 20 sites (colony #2–5) had been documented prior to this study. Nine of 20 colony sites (45%) were located over or along the GPDR, whereas the remaining 11 colonies (55%) were located near the river (mean = 5.8 km ± 4.8 SD, range = 0.3–15 km; Fig. 1, Appendix 1). Eighteen of the 20 colony sites (90%) were water-based (all but two at bridges), and 9 of the potential 11 water-based sites over or along the GPDR were occupied. Two of the 20 colony sites (10%) were land-based (1 building, 1 highway overpass). The breeding range expansion front along the GPDR corridor extended into the Lower Coastal Plain of South Carolina south to the US 76/301 bridge at the junction of Florence and Marion counties (colony site #8), a distance of 65 km from the previous breeding range limit at Cheraw (Fig. 1), a rate of approximately 3.25 km/yr. However, 2 new disjunct colony sites (#9 and #20) were also located farther south in the Tidewater region, a distance of 145 km from Cheraw and 80 km from colony site #8. The two unoccupied bridge sites over the GPDR were located in the Lower Coastal Plain (US 378/SC 41, in Florence and Marion counties) and along the Coast (US 17, in Georgetown County) of South Carolina (Fig. 1). Using data from the most accurate or latest spring counts at each site plus two winter counts from two Tidewater sites (Appendix 1), the total population size for all 20 colony sites was 1729 active nests: 1307 at bridges (76% of total); 275 at a power station; 94 at one building over land; 35 at one highway overpass; and 18 at one building over water. Winter counts document that the number of complete nests at some sites increased, mainly at some bridges in the Piedmont and one building along the Fall Line of North Carolina. Bridge length at the 8 large bridges over the GPDR ranged from 152 to 284 m; bridge length at the 8 moderatesized bridges away from the river ranged from 50 to 80 m except in the Tidewater region over the tributary Black River where bridge length was 130 m. The four largest colonies (200–400 active nests each) were located in the Lower Piedmont at the three large bridges over the GPDR most distant from the range expansion front as well as at the face of the power station along the river. At the other 5 large bridges located over the GPDR and the two sites located near the river in South Carolina, the colony population size was 103 nests (6% of total). The remaining 9 colony sites were located in the Piedmont and along the Fall Line, away from the GPDR in North Carolina. All 9 of these colony sites had smaller population sizes than the 4 largest colonies over or along the GPDR in North Carolina, yet most of D.B. McNair 2013 Southeastern Naturalist Vol. 12, No. 3 504 Figure 1. Location of the 20 Cliff Swallow colony sites over, along, or near the Great Pee Dee River in the Carolinas at and near the range expansion front. Solid symbols refer to colony sites over or along the river (filled square = bridge sites, filled diamond = power station), and open symbols refer to colony sites near the river (open square = bridge sites, open star = highway overpass, open triangle = building without a water body, open circle = building with a water body). See Appendix 1 for additional information on each colony site. Two unoccupied bridges over the Great Pee Dee River in the Lower Coastal Plain of South Carolina are designated by a solid cross. 505 D.B. McNair 2013 Southeastern Naturalist Vol. 12, No. 3 them had larger population sizes than colonies over or near the GPDR in South Carolina despite the much greater length of bridges at the latter colony sites. The 4 moderate-sized bridge colony sites in Richmond County (#14–17) were located along the same drainage system that emptied into the GPDR, approximately 3.8 km south of the southernmost large colony at the US 74 bridge (#4). These populations decreased in size with increasing distance from the river even though the bridges were approximately the same length (45–50 m). Structural characteristics of the fixed-deck-beam bridges (for generic diagram, see North Carolina Department of Transportation 2012), adjusted for bridge length, influenced colony size and nest density (Table 1). At 6 colony sites (#1–2, 11–12, and 14–15), Cliff Swallows built all or most of their nests on the superstructure, on the outside under the overhang of the deck beams; at 7 colony sites (#4–9, 20) all or most of the nests were built on the substructure, on the outside underneath bent caps on top of columns or piles; and at 3 colony sites (#10, 16–17) all or most of the nests were built underneath and to the inside of Table 1. Three groups (outside superstructure, outside substructure, inside superstructure or substructure) 1 of Cliff Swallow colony sites at 16 bridges along the Great Pee Dee River corridor at and near the range expansion front in the Carolinas. Colony Number of active nests / site #2 Bridge length (m) bridge length (m) Outside superstructure (n = 6) 1 273 1.1 / m 2 213 1.7–2.1 / m 11 50 0.5–0.7 / m 12 46 0.7–0.8 / m 14 50 1.7–2.2 / m 15 50 1 / m Range: 46–273 0.5–2.2 / m Outside substructure (n = 7)3 4 284 0.8 / m 5 152 0.1 / m 6 186 0.1–0.2 / m 7 189 0.07 / m 8 185 0.01 / m 9 160 0.11 / m 20 130 0.07 / m Range: 130–284 0.01–0.2 (0.8) Inside superstructure or substructure (n = 3) 10 80 0.8 / m 16 45 0.6 / m 17 50 0.2 / m Range: 45–80 0.2–0.8 / m 1Cliff Swallows built all or most of their nests at each colony site within the assigned group. 2See Appendix 1 for information on each colony site. 3Colony Site #4 had large tall rectangular concrete columns with long and wide bent caps in contrast to colony site #5–9 and 20 which had smaller, shorter cylindrical concrete columns with shorter and narrower bent caps. D.B. McNair 2013 Southeastern Naturalist Vol. 12, No. 3 506 the superstructure or substructure, usually between the corner floors of the deck and long parallel or short cross-bracing horizontal beams that had vertical faces at least 0.5 m deep. Except for a small number of nests at several large bridges, nests were built directly over water and were most concentrated closest to the center of the bridge. Considerable heterogeneity in nest density at each colony site exists among and within the three groups, but the four densest colonies were located on the outside superstructure. One of the largest colony sites (#4) had no nests built on the outside of the superstructure because it lacked the structural characteristics apparently preferred by Cliff Swallows, yet had more favorable outside substructure characteristics than the sites where colonies were located on outside substructures (though these colonies were located at or closer to the range expansion front). The 4 remaining colony sites were not built on bridges: 3 of them were built on the outside of these structures, and one (site #18), which was built over land, had all nests inside the structure. Historical data I obtained historical breeding information (before 2012) on 3 of the 20 (15%) Cliff Swallow colony sites I documented in 2012, and all of them were in the Piedmont (Table 2). All historical colony sites were water-based sites located along or over the GPDR. Compared to colony sizes documented in the early 1980s and mid-1990s at these three sites, colony size had increased approximately 1500% and 400%, respectively, by 2012. Discussion Most avian range expansions are slow even in response to favorable anthropogenic influence, as documented in this study. The previous breeding range limit of Cliff Swallows along the GPDR corridor occurred at the Fall line at Cheraw between 1988 and 1995 (Cely 2003). Over approximately 20 years, the range expansion front along this corridor has extended 65 direct-line kilometers farther southeast and has reached the Lower Coastal Plain of South Carolina. Formerly, Table 2. Historical data (before 2012) on three Cliff Swallow colony sites along the Great Pee Dee River at and near the range expansion front in the Carolinas. Colony Number Physiographic site #1 Year Date of nests province Reference 2 19832 17–18 May 8 Piedmont LeGrand 1984 2 1994 15 June 100 Piedmont D.B. McNair, unpubl. data 3 1994 3 May 80 Piedmont D.B. McNair, unpubl. data 3 2010 25 April 166 Piedmont Southern 2010 4 1981 28 June 5 Piedmont LeGrand 1982 4 1983 17–18 May 0 Piedmont D.B. McNair, unpubl. data 4 1994 3 May 61 Piedmont D.B. McNair, unpubl. data 1See Appendix 1 for information on each colony site. 2Bridge completely rebuilt during the winter of 1982–1983. 507 D.B. McNair 2013 Southeastern Naturalist Vol. 12, No. 3 the disjunct and temporary coastal breeding sites in South Carolina did not occur along the GPDR drainage system (Cely 2003, Post and Gauthreaux 1989). I documented two new disjunct tidewater colony sites along the GPDR corridor, but they are separated from the nearest interior populations by 80 km. The unoccupied bridge (along US 378/SC 41) between interior and coastal populations along this corridor is structurally favorable for colonization by Cliff Swallows. Furthermore, Cliff Swallows have colonized some minor tributaries along this corridor, yet have not colonized the larger Little Pee Dee River between its confluence with the GPDR north to its origin near the North Carolina line, even though several bridges appear structurally suitable (D.B. McNair, unpubl. data). Thus, the interior and coastal populations are probably distinct yet still expanding, but directed movement is constrained by the GPDR corridor. The recent coastal North Carolina population has continued to increase in size and number of colony sites (LeGrand 2011), but it is unknown if the two tidewater South Carolina colony sites are an extension of these coastal North Carolina populations. Although the GPDR corridor has become the most likely avenue in the Carolinas to connect interior with disjunct coastal breeding populations, the uncertain origin of the current coastal population is confounding the pattern of range expansion in the Lower Coastal Plain of South Carolina and additional surveys should be conducted in that area. My survey confirms previously documented colony-site types in the Carolinas (water-based: bridges, power stations; land-based: buildings), each of which was represented along the GPDR corridor at and near the range expansion front. Land-based sites along this corridor are first documented herein, as is the first documentation of nesting under a highway overpass or building over water anywhere in the Carolinas. As expected, water-based colony sites dominated, with the largest colonies at bridges over the GPDR most distant from the range expansion front and at the power station along the river, also located away from the range expansion front. Sites in Richmond County, NC which were located away from the GPDR yet still close to the largest colonies, supported smaller colonies and included radial colony sites along a drainage system where colony size decreased with increasing distance from the river. Most of these radial sites were larger than colony sites located farther south in South Carolina along the GPDR close to or at the range expansion front, suggesting water- and land-based range consolidation has occurred and is perhaps still occurring in Richmond County; all of the radial sites were first colonized sometime after 1994. The observation that only one highway overpass was found to have a nest colony despite the proximity of others with identical structural characteristics as close as 4.5 and 8.4 kilometers away from the GPDR strongly demonstrates preference for water-based colony sites. Material and design changes at moderate to large-sized bridges, the dominant colony-site type, generally favor continuation of Cliff Swallow breeding range expansion along and near the GPDR corridor in the Carolinas. These bridges are now primarily or entirely built of reinforced concrete, usually with nests on the outside under the overhang of the deck beams D.B. McNair 2013 Southeastern Naturalist Vol. 12, No. 3 508 or underneath bent caps on top of columns or piles. No competition was observed with the Barn Swallow for nest sites at either water- or land-based colony sites (Brown and Brown 1995, 1999), except perhaps at 3 moderate-sized bridge colony sites where most Cliff Swallow nests were built underneath and on the inside of the superstructure or substructure. However, even here, nest-site placement differences were usually pronounced (D.B. McNair, unpubl. data). Furthermore, Barn Swallow populations are fairly common and stable in this geographic area, and its range is no longer expanding (Brown and Brown 1999, Sauer et al. 2011; D.B. McNair, unpubl. data), which also reduces any potential competition with Cliff Swallows for nest sites. The breeding population of Cliff Swallows along and near the GPDR, over 1700 active nests in 2012, is the first comprehensive estimate for this major corridor or for any other large riverine system in the Carolinas. The initial range expansion in North Carolina to the GPDR region in the early 1980s involved low numbers of birds, with major increases in the number and size of colony sites since; hence, breeding Cliff Swallows have much more than “slightly increased” in the Piedmont over the last 30 years (contra LeGrand et al. 2011). Range consolidation is a situation in which a colony grows to a critical mass, after which additional colony sites are sought by new arrivals. Even though major water bodies along the GPDR corridor south of Blewett Falls Lake are absent, the pattern of range consolidation and movement of the interior population is conjectural because historical data are scant and recent comprehensive surveys have only been conducted for one year. Repeat surveys should be conducted to investigate shortand long-term changes in breeding range, colony number, and size. Nonetheless, the substantial and increasing population size, linear breeding range distribution pattern with some short radial protrusions, apparent density-dependent manner of dispersal, and slow rate of range expansion of Cliff Swallows along the GPDR corridor generally supports the stepwise model of population consolidation and expansion of the interior population, not the leapfrogging pattern. The stepwise pattern constitutes sequential linear movements from bridge to bridge rather than the leapfrogging pattern that entails skipping some bridges initially and then backfilling later during the consolidation phase. Future surveys along the GPDR corridor are required to substantiate colony site fidelity, which would support the stepwise model. This southeastern range expansion of the Cliff Swallow in the interior of the Carolinas is the reverse of the northward movement in breeding range for many other avian species (Brommer et al. 2012, Hitch and Leberg 2007), and the expansion of this insectivorous long-distance migrant does not seem to be associated with a decrease in populations of flying insects (Nebel et al. 2010). Cliff Swallow population increases on the periphery of this species' range in southestern North America suggest it may be less vulnerable to large-scale climate change (Van Der Jeugd et al. 2009) compared to many other avian species, but this issue requires detailed investigation. 509 D.B. McNair 2013 Southeastern Naturalist Vol. 12, No. 3 Acknowledgments I thank C.J. Randel for preparing Figure 1 and C.R. Brown, W. Post, M.T. Stanback, and an anonymous individual for their reviews of the manuscript. Literature Cited Animal Diversity Web. 2012. University of Michigan Museum of Zoology. 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Spatiotemporal patterns in nest box occupancy by Tree Swallows across North America. Avian Conservation and Ecology 7(1):3. Available online at http://dx.doi. org/10.5751/ACE-00517-070103. Accessed June 2012. Simmons, A.D., and C.D. Thomas. 2004. Changes in dispersal during species’ range expansions. American Naturalist 164:378–395. Southern, J. 2010. Briefs for the files. Chat 74:82–96. Southern, J. 2011. Briefs for the files. Chat 75:153–161 Van Der Jeugd, H.P., G. Eichhorn, K.E. Litvins, J. Stahl, K. Larsson, A.J. Van Der Graaf, and R.H. Drent. 2009. Keeping up with early springs: Rapid range expansion in an avian herbivore incurs a mismatch between reproductive timing and food supply. Global Change Biology 15:1057–1071. Available online at doi:10.1111/j.1365- 2486.2008.01804.x. Accessed February 2013. Veech, J.A., M.F. Small, and J.T. Baccus. 2011. The effect of habitat on the range expansion of a native and an introduced bird species. Journal of Biogeography 38:69–77. Virtual Birder. 2012. Carolina birds. Available online at http://www.virtualbirder.com/ bmail/carolinabirds. Accessed June 2012. Wagner, S., S. Stegenga, and B. Hilton, Jr. 2002. First breeding records for Tree Swallows in South Carolina. Chat 66:145–148. 511 D.B. McNair 2013 Southeastern Naturalist Vol. 12, No. 3 Appendix 1. Cliff Swallow colony sites along the Great Pee Dee River corridor at and near the range expansion front in the Carolinas. Distance (km) Number Colony from Great of active Physiographic site # State County Road Structure Water body Pee Dee River Date nests province Over or along the Great Pee Dee River 1 NC Stanley / NC 731 Bridge Great Pee Dee River 0 11 May 303 Piedmont Montgomery (22 Dec) (NA)1 2 NC Richmond / NC 109 Bridge Great Pee Dee River 0 2 May; 442; Piedmont Anson 11 May 371 (22 Dec) (545) 3 NC Anson 1748 Power Station2 Great Pee Dee River 0 21 April; 275; Piedmont 11 May 2113 (31 Dec) (155) 4 NC Richmond / US 74 Bridge4 Great Pee Dee River 0 13 April; 885; Piedmont Anson 9 May 2176 (31 Dec) (148) 5 SC Chesterfield / US 1 Bridge Great Pee Dee River 0 8 May 20 Fall Line Marlboro (26 Dec) (21) 6 SC Darlington / US 15 / Bridge Great Pee Dee River 0 7 May; 24; Coastal Plain Marlboro 501 18 May 41 (4 Jan) (68) 7 SC Darlington / SC 34 Bridge Great Pee Dee River 0 18 May 13 Coastal Plain Marlboro (4 Jan) (15) 8 SC Florence / US 76 / Bridge Great Pee Dee River 0 18 May 2 Coastal Plain Marion 301 (4 Jan) (10) 9 SC Georgetown / US 701 Bridge Great Pee Dee River7 0 (9 Jan) (17) Tidewater Horry D.B. McNair 2013 Southeastern Naturalist Vol. 12, No. 3 512 Distance (km) Number Colony from Great of active Physiographic site # State County Road Structure Water body Pee Dee River Date nests province Near the Great Pee Dee River 10 NC Stanley / US 52 Bridge Rocky River 6.6 11 May 67 Piedmont Anson (22 Dec) (195) 11 NC Richmond 1148 Bridge Little River 1.7 27 April; 26; Piedmont 11 May 33 (22 Dec) (118) 12 NC Richmond 1148 Bridge Mountain Creek 0.3 27 April; 38; Piedmont 11 May 30 (22 Dec) (53) 13 NC Richmond US 74 Highway None 1.8 9 May 35 Piedmont Overpass8 (20 Dec) (33) 14 NC Richmond 1109 Bridge Pee Dee Creek9, 10 1.8 26 April; 87; Fall Line 10 May 111 (24 Dec) (84) 15 NC Richmond 1124 Bridge Midway Pond9 5.6 10 May 51 Fall Line (19 Dec) (55) 16 NC Richmond 1436 Bridge Roberdel Pond9 12.6 27 April; 75; Fall Line 10 May 27 (19 Dec) (30) 17 NC Richmond 1442 Bridge Ledbetter Lake9 15.0 10 May 12 Fall Line (19 Dec) (7) 18 NC Richmond 1109 Building11 None 2.412 11–17 April; 7313; Fall Line 9 May 94 (2 Jan) (184) 19 SC Darlington 21–26 Building14 Pitman Pond 7.4 19 May 18 Coastal Plain (4 Jan) (15) 20 SC Georgetown US 701 Bridge Black River 8.5 (9 Jan) (9) Tidewater 513 D.B. McNair 2013 Southeastern Naturalist Vol. 12, No. 3 1NA (not available); all nests had been removed during renovation work on bridge. 2Spillway at the power station beside Blewett Falls Dam (Progress Energy). 3Some active nests were removed on one face of the power station when new window screens were installed, which prevented renesting. 4All nests were located on the southern bridge; the northern bridge was not used by Cliff Swallows. 5Incomplete count. 6Twenty-nine active nests were over the ground, not water. 7After confluence with the Little Pee Dee River. 8Two side-by-side overpasses had a total of five columnar concrete columns with overhanging bent caps, all used by nesting Clif f Swallows. 9Pee Dee Creek, Midway Pond, Roberdel Pond, and Ledbetter Lake are part of the same drainage system. 10Pee Dee Pond formerly occurred just upstream from Pee Dee Creek; several scattered pools remain, and another small pond (Steeles Mill Pond) occurs further upstream. 11Burlington Mill of the International Textile Group, Cordova. The detached outdoor concrete storage shed was entirely open on one side and measured approximately 21 m long by 18.75 m wide by 16 m high. Cliff Swallows nested on the overhead parallel beams which were approximately 0.5 m deep. 12Colony site was approximately 0.8 kilometer away from colony site number 16. 13The storage shed was outfitted with a lighting system and the colony was completely destroyed by 26 April, when no Cliff Swallows were present; the colony had reformed by 9 May when the storage shed contained larger amounts of coal and wood chips. The new lighting system did not disturb nesting Cliff Swallows, which were unmolested afterwards. 14The Robert B. Pitman building, Pee Dee Research and Education Center, Clemson University. Part of the building, with short concrete columns, was built over a pond. Most Cliff Swallows did not nest on the columns but on the topside of two alcoves, which nonetheless faced directly over water.