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Establishing a Baseline and Faunal History in Amphibian Monitoring Programs: The Amphibians of Harris Neck, GA
C. Kenneth Dodd, Jr. and William J. Barichivich

Southeastern Naturalist, Volume 6, Number 1 (2007): 125–134

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2007 SOUTHEASTERN NATURALIST 6(1):125–134 Establishing a Baseline and Faunal History in Amphibian Monitoring Programs: The Amphibians of Harris Neck, GA C. Kenneth Dodd, Jr.1,* and William J. Barichivich1 Abstract - We conducted an intensive inventory of Harris Neck National Wildlife Refuge in coastal Georgia to determine the feasibility of establishing an amphibian monitoring program at this location. Thirteen semi-aquatic amphibian species were identified at 21 locations. Amphibian species richness at Harris Neck was similar to that of nearby barrier islands. The amphibian fauna of Harris Neck has long been affected by human-induced landscape changes, including the inadvertent introduction of tadpoles from distant fish hatcheries and the creation of artificial impoundments. Land-use history provides important information necessary to understand current amphibian distribution, especially when census data are used to establish a baseline from which to monitor future status and trends. Introduction The decline and extinction of many amphibian taxa throughout the world has sparked considerable interest in the biology and biogeography of these species (Houlahan et al. 2000, Stuart et al. 2004). The causes of declines are complex and may be interrelated (Blaustein and Kiesecker 2002, Collins and Storfer 2003, Corn 2000, Pounds et al. 2006). There is a crucial need for current information on the distribution of amphibians across a landscape, so that species and populations can be monitored for signs of imperilment. Accordingly, much attention has been directed at how to monitor amphibians (Dodd et al., in press), and whether status should be measured in terms of changes in abundance or site occupancy (e.g., MacKenzie et al. 2005, Schmidt 2003, Schmidt et al. 2002). As part of the interest in monitoring amphibians, the US Congress authorized the US Geological Survey to undertake a national assessment of the status of amphibians within the United States, and to develop a research program designed to detect trends and identify factors which might be causing declines. This program, the Amphibian Research and Monitoring Initiative (ARMI) (Corn et al. 2005, Muths et al. 2005), currently focuses on Department of Interior lands, which in the Southeast are largely under the jurisdiction of the National Park Service and US Fish and Wildlife Service. We identified four National Wildlife Refuges (NWR) on the Coastal Plain to determine their feasibility as long-term monitoring sites, including Harris Neck NWR (HNNWR) in mid-coastal Georgia. Historical information on the amphibians of HNNWR is nearly nonexistent, as we have found records of only two Hyla cinerea (Schneider) (Green 1US Geological Survey, 7920 NW 71st Street, Gainesville, FL 32653. *Corresponding author -Terrapene600@gmail.com. 126 Southeastern Naturalist Vol. 6, No. 1 Treefrogs) collected from Harris Neck (J. Jensen, Georgia Department of Natural Resources, Forsyth, GA. pers. comm.), and there are no publications discussing its amphibian fauna. Knowledge of which species occur within an area and the location of potential long-term monitoring sites must be available before a monitoring project can be established (Dodd et al., in press). Inasmuch as no herpetological inventory had been conducted at HNNWR, our initial objective was to identify potential sampling sites and species present. During conversations with refuge staff, we became aware of the complex human-related impacts to the land at Harris Neck, including impacts that had taken place at least since the area was settled by Europeans and Africans in the 1700s. Many of the likely impacts were immediate and related to refuge development and operations during the last 40 years. However, we also began to question how human impacts as long ago as 300 years might have affected the persistence of Harris Neck’s amphibian fauna. If initial monitoring results establish a baseline with which future trends may be compared, does this baseline represent a fauna that is “natural” (i.e., representative of populations undisturbed by humans), highly disturbed, or somewhere in-between? This question becomes particularly important since monitoring programs generally assume that the results taken within one area can be extrapolated to a wider area of inference (Thompson et al. 1998). In this paper, we report on the results of our inventory, and note the importance of having an understanding of long-term human history on sites chosen for a monitoring program. Materials and Methods Study site Harris Neck NWR is located ca. 46 km south of Savannah and 31 km north of Darien, in McIntosh County, GA (Fig. 1). The refuge comprises 1255 hectares of mostly coastal deciduous and oak woodlands, grasslands, former cropland, and both naturally regenerated and planted pine; it is surrounded by salt marshes and tidal creeks. Harris Neck became a National Wildlife Refuge in 1962, and is currently managed primarily for waterfowl and wading birds, including Mycteria americana Linnaeus (Wood Stork). Nearly all the wetlands at Harris Neck are man-made impoundments, modified former tidal creeks, or ditches and borrow pits. The land now comprising HNNWR has had many uses. Most impacts on amphibians likely resulted from habitat alteration, as the land changed from a subtropical maritime forest to plantation, later to small-farm agriculture, then to an area of intensive technological development and potential exposure to toxic chemicals (gasoline and the by-products of a military base), to abandonment, and finally to a region characterized by intensive semi-natural wildlife management. In order to understand the distribution of amphibians at HNNWR, we examined all available materials relating to land use since the area was 2007 C.K. Dodd, Jr. and W.J. Barichivich 127 settled by Europeans and their African slaves about 1740 (see Sullivan 1997 for a thorough review). Land grantees established plantations through the latter part of the 1700s for sea-island cotton and rice production. Plantation agriculture continued until the Civil War. None of the crude maps we have seen indicate the presence of any freshwater wetlands on the property, although the location of artesian wells is noted. After the Civil War, plantations were subdivided and largely occupied by former slaves. Agriculture shifted from labor-intensive cash crops to subsistence farming and timbering, with some free-range hogs and cattle. In 1890, the tobacco tycoon Pierre Lorillard established a summer mansion on HNNWR, and records indicate the presence of outdoor fountains and pools. In the 1930s, an airfield was established at HNNWR for passenger airliner emergency use. In 1942, the Army constructed Harris Neck Air Base, near the former civilian airfield, on 545 ha taken from African- American farmers, and the community of Harris Neck ceased to exist. After years of county fiscal and environmental mismanagement after World War II (Sullivan 1997), the Federal government reclaimed the land in 1962 and turned it over to the US Fish and Wildlife Service. No records mention wetlands or streams. Large sections of the former air base are covered by deteriorating tarmac. Figure 1. Map of Harris Neck National Wildlife Refuge, McIntosh County, GA showing the location of aquatic sampling sites. Lines within the map indicate the system of roads. All wetlands were regularly sampled; no amphibians were found at Bluebill Pond because of its brackish water. H indicates refuge headquarters compound. 128 Southeastern Naturalist Vol. 6, No. 1 Surveys Most amphibians of the southeastern Atlantic Coastal Plain breed in wetlands (streams, ponds, lakes, swamps). We therefore focused sampling in aquatic habitats to inventory amphibian species richness, identify potential sites for long-term monitoring, and determine the distribution of breeding sites on the refuge. This focus allowed us to maximize species-detection probabilities and examine important covariates (e.g., pH, fish predators) influencing presence. We conducted six 3-day surveys from March to October in 2004 and 2005, supplemented by a few short observational surveys at other times. All wetlands were visited multiple times each year. Aquatic sampling consisted of: the use of dip nets (HDD-2 with 3/16” sq. Delta mesh; Memphis Net and Twine Co., Memphis, TN) by 2–4 people for a total of 10–30 min per site, depending on the size of the wetland; 2–4 crayfish traps/site for ca. one continuous 48-hr period (Johnson and Barichivich 2004); diurnal and nocturnal aural surveys for two nights (incidental observations and by using automated frog-call data loggers at 5 sites per visit; Barichivich 2003); and visual encounter observations. We collected water-quality data at 12 ponds (water temperature [ºC], conductivity [mS/cm], pH, dissolved oxygen [mg/l], and % dissolved oxygen) using a Hydrolab® Quanta® water-quality meter; these parameters were measured at 10 ponds on more than one visit. Terrestrial sampling supplemented wetland surveys, and included field searches (i.e., visual encounter surveys for animals in the open and under cover objects, e.g., logs, rocks) and road cruises (i.e., making opportunistic observations while driving roads, typically at night). We searched a number of terrestrial locations, particularly woodlands in the northeast near an old army bunker, the terrestrial areas below Woody dike, various areas along the wildlife drive, and areas adjacent to Lucas Pond. Results Thirteen amphibians (12 species of frogs and one species of salamander) were recorded during our surveys at HNNWR (Table 1). Species richness was similar to some of the southern Atlantic Coast barrier islands, although a great deal of variation occurs among islands (Fig. 2). Rana sphenocephala Cope (Southern Leopard Frog) was found at the most sites at Harris Neck (14), followed by H. cinerea at 11 sites. Hyla gratiosa LeConte, (Barking Treefrog) was not seen during 2004, and only a single calling individual at Borrow Pond (Fig. 1) has thus far been observed. Hyla squirella Bosc (Squirrel Treefrog) was rarely heard around any of the wetlands, but was commonly observed around refuge headquarters at night. The most amphibians recorded at single sites (8) were found at a small, fishless borrow pit pond (Borrow Pond) and at a large impoundment (Goose Pond, bordered on the north by shallow flooded grasses). Only one species was found in a shallow, seasonally flooded roadside ditch, a fountain pool at 2007 C.K. Dodd, Jr. and W.J. Barichivich 129 Table 1. Amphibian species occurrence at sampling sites on Harris Neck National Wildlife Refuge, McIntosh County, GA, 2004–2005. No amphibians were found in purely terrestrial habitats, except while crossing roads on rainy nights or at the refuge headquarters. A.g. = Acris gryllus, B.t. = Bufo terrestris, G.c. = Gastrophryne carolinensis, H.c. = Hyla cinerea, H.f. = Hyla femoralis, H.g. = Hyla gratiosa, H.s. = Hyla squirella, N.v. = Notophthalmus viridescens, P.c. = Pseudacris crucifer, P.o. = Pseudacris ocularis, R.c. = Rana catesbeiana, R.g. = Rana grylio, R.s. = Rana sphenocephala, and # = No. of species observed. Site A.g. B.t. G.c. H.c. H.f. H.g. H.s. N.v. P.c. P.o. R.c. R.g. R.s. # Borrow Pond X X X X X X X X 8 Church Ditch X 1 Culvert Pond X X 2 Goose Meadow X X X 3 Goose Pond X X X X X X X X 8 Greenhead Pond X X X X X X 6 Lucas Borrow X X X 3 Lucas Pond X X X X X X 6 Lucas Seepage X X 2 N Runway Ditch X X X X 4 Plantation Fountain X 1 Red Maple Swamp X X X 3 Snake Bog X X X X X 5 Snipe Pond 1 X X 2 Snipe Pond 2 X 1 Snipe Pond 3 X X X X X 5 Teal Pond X X X X X 5 Wigeon Pond X X X X X X 6 Woody Pond X X X X X X X 7 Woody Swamp X X X 3 Refuge Headquarters X X X 3 No. of sites 7 5 6 11 3 1 2 7 9 9 6 4 14 w/ observations Figure 2. The relationship between amphibian species and barrier island size (ha) for barrier islands extending from Maryland to Georgia (N = 25). Whereas the regression is significant (F = 5.35, p = 0.03), little of the variance is explained (r2 = 0.189).The rectangle indicates Harris Neck. Data from Gibbons and Coker (1978), Gibbons and Harrison (1981), Conant et al. (1990), Mitchell and Anderson (1994), Laerm et al. (2000), and Shoop and Ruckdeschel (2003). 130 Southeastern Naturalist Vol. 6, No. 1 the Lorillard homesite, and in one segment of a sometimes interconnected much larger impoundment (Snipe Pond). Amphibians were recorded at every wetland on the refuge, even at a shallow pool at the end of a culvert (Culvert Pond) and ditches adjacent to the old air base north runway (North Runway Ditch). Fish were present in all wetlands at HNNWR except at Borrow Pond. No terrestrial amphibians were observed during visual encounter surveys; however, amphibians were particularly abundant on paved roads after heavy rains, and many species were detected calling. We found several species (e.g., B. terrestris Bonnaterre [Southern Toads], H. cinerea) distributed essentially throughout the refuge in 2005, despite the fact that only a single B. terrestris was observed during all surveys in 2004. During a single pass on the wildlife drive (16 May 2005), for example, we heard 7 species calling: Acris gryllus LeConte (southern cricket frog), B. terrestris, H. cinerea, H. femoralis Bosc, Pseudacris ocularis (Bosc and Daudin) (Little Grass Frog), Rana catesbeiana Shaw (American Bullfrog), and R. grylio Stejneger (Pig Frog). 2004 We made one scouting trip to the refuge in January 2004, followed by three intensive sampling periods in 5–7 April, 29–30 June, and 19–20 October, and a very short visit to Borrow Pond and Plantation Fountain on 24 November. We detected 12 amphibian species comprising 11 species of frogs and one salamander at 19 wetland sites. We collected water-quality field parameter data at one location in April and 9 locations in both June and October. pH values generally were acidic (4.5–6.8) except at Blue Bill (April, 7.5), Goose (October, 7.3), Snipe (June, 7.8), and Teal (October, 7.2). The lowest pH was 4.5 in Borrow Pond in October. Dissolved oxygen values were very low in all wetlands (0.34–4.95 mg/l), but conductivity was relatively high everywhere (to 0.469 mS/cm), except for Borrow Pond (0.019, 0.03). Percent DO values were very low (< 25%), except at Snipe Pond (101.3%) and Borrow Pond (62.2%) in June. Pond water temperatures varied between 19.3 and 27.6 ºC during sampling. 2005 Fifteen wetland sites were sampled in 21–23 March, 12 in 16–18 May, and 9 in 25–27 July. Three new wetland sites were identified after frogs were heard calling from them during a period of heavy rainfall: Church Ditch (along main road across from Friendship Baptist Church), Goose Meadow (adjacent to the dirt road along the southeast side of Goose Pond), and Snake Bog (a seepage boggy habitat along the main road near Friendship Baptist Church). Church Ditch only held water after heavy rains in March, and P. ocularis were heard calling from its margins. Goose Meadow is an extensive shallow water area, but it only holds water after substantial rainfall. Bufo terrestris bred successfully there in March in large numbers. Water remained in May, but no tadpoles were seen; by July, the area was dry and small juvenile toads were observed. Snake Bog had 2007 C.K. Dodd, Jr. and W.J. Barichivich 131 choruses of P. ocularis, H. femoralis, H. cinerea, and A. gryllus during night surveys in May, but no tadpoles were seen. Values for pH again were generally acidic, with a range of 3.9 to 8.7 and a mean among all samples of 6.0. Conductivity was generally low, less than 0.397 mS/cm at all sites. Dissolved oxygen (DO, mg/l) and % DO varied considerably, ranging from 0.11 mg/l and 1.4% to 14.87 mg/l and 159%. Water temperatures ranged from 13.8 ºC to 28.9 ºC. Discussion The only published records of amphibian faunas from the coastal regions of Georgia are for the barrier islands (Laerm et al. 2000, Shoop and Ruckdeschel 2003) and two small national park units (Tuberville et al. 2005). Although not a barrier island, Harris Neck is not physically connected to the mainland, but is separated by a tidal channel and a salt marsh. All of the species on HNNWR have been found on many of Georgia’s barrier islands (Laerm et al. 2000, Shoop and Ruckdeschel 2003), particularly Sapelo Island (Fig. 1), located ca. 23 km to the southeast (Laerm et al. 1999, Martof 1963). Two species found on Sapelo—Amphiuma means Garden and Scaphiopus holbrookii (Harlan)—have not been found at Harris Neck. The US Fish and Wildlife Service developed Harris Neck as a waterfowl and heron refuge. Impoundments were created by closing off the downstream portions of tidal creeks and deepening the upstream portions (Bluebill, Woody, Wigeon, Lucas), creating shallow ponds (Goose, Greenhead) with interconnecting canals (Teal), and filling the depressions with fresh water from artesian wells. These impoundments are periodically drawn down and may be further excavated to remove vegetation and debris. Borrow pits (Borrow, Lucas Borrow, North Runway Ditch), depressions resulting from road construction (Church, Culvert, possibly Snake Bog), seepages under dams (Woody Swamp, Lucas Seepage), and a fountain at the site of the former Lorillard mansion are the only other wetlands on HNNWR. Waterfowl and water bird management have undoubtedly affected amphibian presence at HNNWR by providing abundant aquatic breeding sites, including a few small areas that are free of fish, in an area previously devoid of extensive wetlands. Fishless wetlands allow pond breeders such as H. femoralis and H. gratiosa access to an area in which they otherwise could not reproduce. At the same time, management practices such as fish stocking may have inadvertently mixed faunas. We found tadpoles resembling upper coastal plain phenotypes of larval R. catesbeiana (olive bodies with small salt and pepper spotting) in ponds where fish had been stocked, adjacent to ponds (into which fish had not been stocked) containing phenotypes of R. catesbeiana from the lower coastal plain (deep green dorsally and bright yellow ventrally). This could be the result of faunal mixing, inasmuch as fish are imported from Bo Ginn, GA, and Orangeburg, SC; fish shipments have not been screened for tadpoles or adult amphibians. 132 Southeastern Naturalist Vol. 6, No. 1 Despite all the human-created landscape changes at HNNWR, amphibians are still relatively abundant. Somewhat brackish-tolerant species are common and widely distributed (e.g., R. sphenocephala, B. terrestris), whereas fish-intolerant species (H. femoralis, H. gratiosa) are present but rare. As on most barrier islands, caudate species richness is low. The fauna is similar to what Shoop and Ruckdeschel (2003) term the Pleistocene and Holocene relict amphibian faunas, that is, faunas which reflect the complex changes in sea level which have occurred over the last several million years. The absence of certain species (e.g., A. means, S. holbrookii Harlan) from the HNNWR fauna likely reflects the absence of historic wetlands on HNNWR, changes during the long period of human use, or a combination thereof. The current HNNWR fauna likely resulted from geologic changes during the Pleistocene and Holocene, nearness to mainland faunas, and human activities, particularly the introduction of tadpoles during fish stocking and the creation of artificial impoundments. When developing long-term monitoring programs, it is important to understand the biogeography and recent history of the fauna to be monitored. If faunas are highly “artificial,” not representative of the wider community, or recently disturbed, then the area of inference from baseline inventories may have limited applicability. Understanding the history of land-use in a monitoring program provides important covariates to understanding current amphibian distribution, status, and trends. 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