Pine Barrens Treefrog
© 2009 Stephen Bennett (1 of 7)
Hyla andersonii Baird, 1854(b)
D. Bruce Means1
1. Historical versus Current Distribution. The type locality of Pine Barrens treefrogs (Hyla andersonii) is Anderson, South Carolina, but most authorities believe that neither the holotype specimen nor the species ever occurred there (Noble and Noble, 1923; Neill, 1948a, 1957a; Wright and Wright, 1949; Gosner and Black, 1967; E.E. Brown, 1980; Karlin et al., 1982). Today, populations are known from three widely disjunct areas of the southeastern United States (New Jersey Pine Barrens, the Fall Line sandhills of North and South Carolina, and the Florida Panhandle and adjacent south Alabama), but the knowledge of this species’ distribution has come slowly. The second record and first New Jersey specimen was reported by Cope (1862). Then, the first North Carolina record was reported 60 yr later (Davis, 1922), and it was 86 yr after its formal description before anyone verified that the species really did occur in South Carolina (Brimley, 1940). Amazingly, Pine Barrens treefrogs were not discovered in Florida and southern Alabama until 116 yr after they were named (Christman, 1970), but even the determination of its Florida/Alabama distribution required time and was fraught with difficulty (Means and Longden, 1976; Means, 1978, 1983; Means and Moler, 1979; Moler, 1981; Printiss and Hipes, 1999). Because the geographical distribution of Pine Barrens treefrogs is just now becoming understood, we have no way of comparing historical versus present distributions.
2. Historical versus Current Abundance. The fact that local populations call erratically is probably the most important reason why knowledge about the biology and distribution of Pine Barrens treefrogs have been slow to accumulate. Means and Longden (1976) and Means and Moler (1979) noted that known breeding sites in Florida were sometimes silent on nights when frogs were calling elsewhere. Moler (1981) in Florida and Cely and Sorrow (1983) in South Carolina verified this and demonstrated that the seepage status of breeding sites may be a more important variable in predicting calling behavior than temperature, humidity, and thundershower activity. At one time it was believed that the New Jersey population was the largest of the three isolates (Wright and Wright, 1949; Means and Longden, 1976). Fieldwork in the Carolinas (Montanucci and Wilson, 1980; Tardell et al., 1981; Cely and Sorrow, 1983), Florida (Means and Moler, 1979; Moler, 1981; Printiss and Hipes, 1999), and Alabama (Mount, 1980; Jensen, 1991), however, has shown in the past two decades that Pine Barrens treefrogs are more abundant in these enclaves than was once believed. Populations in all three regions have dwindled from pre-settlement levels because of agriculture, development, and plant succession following the interruption of the natural fire cycles in Pine Barrens treefrog habitats (Means and Longden, 1976; Means and Moler, 1979; Ehrenfeld, 1983; Ehrenfeld and Schneider, 1983; Freda and Morin, 1984; Cely and Sorrow, 1986).
3. Life History Features.
i. Breeding migrations. None known, but adult frogs disperse ≤ 105 m away from breeding ponds within 30 d after breeding (Freda and Gonzalez, 1986), and therefore must return to breed again.
ii. Breeding habitat. An important characteristic of most breeding sites is low pH (Wright and Wright, 1949; Gosner and Black, 1957b; Means and Longden, 1976; Means and Moler, 1979; Freda and Morin, 1984; Cely and Sorrow, 1986). In New Jersey, Pine Barrens treefrogs breed in small shallow ponds, acid pools, seepage streams, and bogs usually surrounded by heavy shrub growth (Gosner and Black, 1957b; Freda and Morin, 1984). The largest breeding colonies are found in open canopy, early successional sites dominated by shrubs and herbs; the water is always acidic (< pH 4.5) with dense mats of sphagnum or other aquatic vegetation (Freda and Morin, 1984). Breeding habitat in the Carolinas is evergreen shrub-herb bog along small blackwater tributaries in the sandhills. Florida and Alabama breeding sites are similar to those in New Jersey and the Carolinas: acid, hillside seepage bogs with small pools of clear, acid seepage water and a diverse wetland flora of Sphagnum spp., sedges, rushes, bladderwort, pipeworts, sundews, pitcher plants, clubmoss, and filamentous algae. These sites are usually at the interface between heliophilic herb bogs upslope from evergreen shrub bogs that are dominated by black titi (Cliftonia monophylla), swamp titi (Cyrilla racemiflora), tall gallberry (Ilex coriacea), and sweet bay (Magnolia virginiana; Means and Longden, 1976; Means and Moler, 1979; Moler, 1980; Mount, 1980). Generally, herb bogs are characterized by sundews (Drosera spp.), pitcher plants (Sarracenia purpurea), orchids, sedges, and grasses, especially beakrush (Rhynchospora spp.), broomsedge (Andropogon spp.), and needlerush (Juncus spp.), with sphagnum moss present at most sites (Gosner and Black, 1956; Montanucci and Wilson, 1980; Tardell et al., 1981; Cely and Sorrow, 1983, 1986). In all three enclaves, researchers noted that breeding habitat is often associated with disturbances such as logging clearcuts, or gas, powerline, or railroad rights-of-way (Means and Moler, 1979; Tardell et al., 1981). Means and Moler (1979) believe this is because the specialized breeding sites of Pine Barrens treefrogs depend upon adequate seepage water that is reduced through evapotranspiration when herb bogs become encroached by woody plants. They argued that fire was the dominant force in pre-settlement times maintaining herb bogs in early successional stages, which is mimicked by logging, bush-hogging, and mowing (Means and Moler, 1979). Researchers in the Carolinas (Cely and Sorrow, 1986) and New Jersey (Freda and Morin, 1984) concurred.
i. Egg deposition sites. Noble and Noble (1923) and Gosner and Black (1957a) described and figured the diagnostic stages and characters of developing eggs, larvae, and recently metamorphosed froglets in New Jersey. Oviposition occurs in New Jersey from about 20 May–8 July (Wright, 1932), but published information is not available for the Carolinas, Florida, or Alabama.
ii. Clutch size. From 800–1,000 (Wright and Wright, 1949). Hatching occurred in 4 d in the laboratory (Noble and Noble, 1923) and has been estimated to take place in 3 or 4 d in nature (Wright, 1932).
C. Larvae/Metamorphosis. Larvae were collected in Florida from the last week in May to the third week in August (Means, 1992a). The earliest date for transformation in New Jersey is 25 June, and the average length of the larval period in laboratory-raised groups reared at room temperature was 48 d (Wright and Wright, 1949). Wright (1932) estimated length of larval period in the field to be 50–75 d, with transformation occurring from 20 June–31 August. It is estimated that Florida larvae metamorphose by the end of September (Means, 1992a).
D. Juvenile Habitat. Post-metamorphic juvenile habitat is not known to differ from that of adults.
E. Adult Habitat. The preferred habitat of adult Pine Barrens treefrogs when not engaged in breeding is unknown. Most observations of adult Pine Barrens treefrogs have been made on calling males whose habitat preferences were likely to have been biased by their drive to breed. In spite of this, researchers report the habitat of adults to be shrub bogs dominated by mixtures of the evergreen woody plants where calling males and amplexed females have been found. Shrub bogs in South Carolina (Cely and Sorrow, 1986) are characterized by a sparse overstory of yellow poplar (Liriodendron tulipifera), red maple (Acer rubrum), blackgum (Nyssa sylvatica ), and pond pine (Pinus serotina); an understory of red maple, sweet bay, yellow poplar, swamp titi (Cyrilla racemiflora), pine, blackgum, and black alder (Alnus serrulata); and a shrub layer of sweet pepper bush (Clethra alnifolia), cinnamon fern (Osmunda cinnamomea), greenbriar (Smilax spp.), red maple, switch cane (Arundinaria gigantea), wax myrtle (Myrica cerifera), fetterbush (Lyonia lucida), and tall gallberry (Ilex coriacea). In addition to most of these species, in New Jersey shrub bogs there was a greater representation of Atlantic white cedar (Chamaecyparis thyoides) and Vaccinium spp. (Wright, 1932); in Florida black titi and swamp titi were usually the most common shrubs (Means and Longden, 1976).
F. Home Range Size. Has not been studied, except that Freda and Gonzalez (1986) generated data on movement away from breeding ponds by eight adults (seven males, one female) over periods of 4–30 d.
G. Territories. Unknown.
H. Aestivation/Avoiding Dessication. Pine barrens treefrogs are active March–November and have been observed calling and breeding throughout these months during rainy periods (Means, 1992a). Whether individuals seek certain microhabitats as refuges or become inactive during droughts and between rainy periods is unknown.
I. Seasonal Migrations. Not known to occur, except adults may move at least 105 m through shrub bogs to breeding ponds (Freda and Gonzalez, 1986).
J. Torpor (Hibernation). Almost nothing is known about the circumstances of overwintering in Pine Barrens treefrogs, but Neill (1948b) reported a Richmond County, Georgia, specimen that was “found beneath loose bark of a standing tree on a cool day.” Other than this casual mention, the species has not been reported from Georgia despite intense searching by herpetologists over the past half century.
K. Interspecific Associations/Exclusions. Few other frogs have been found associated with Pine Barrens treefrogs in larval habitats because of the high acidity of the water (Gosner and Black, 1957a,b; Pehek, 1995). However, tadpoles of pine woods treefrogs (Hyla femoralis), squirrel treefrogs (H. squirella), and southern cricket frogs (Acris gryllus) were reported in larval habitats with Pine Barrens treefrog tadpoles from Florida (Means and Longden, 1976). Adult green frogs (Rana clamitans) and southern leopard frogs (Rana sphenocephala) were associated with Pine Barrens treefrogs in New Jersey breeding ponds (Freda and Morin, 1984).
L. Age/Size at Reproductive Maturity. In aquaria and terraria, Means and Longden (1976) raised tadpoles to adult size in 1 yr, but did not know if they were sexually mature.
M. Longevity. Adult frogs have been kept in captivity for periods of up to 20 mo (personal observations), 2 yr (Wright, 1932), and 7 yr (Moler, 1980).
N. Feeding Behavior. In aquaria, tadpoles readily eat boiled lettuce, filamentous algae brought in from larval habitats, and commercial pet fish food (Means and Longden, 1976). Newly metamorphosed animals were successfully raised to adult size on tiny insects that accumulated at night lights (Means and Longden, 1976). Ten males examined from New Jersey had grasshoppers, beetles, ants, dipterans, and unidentified insect remains in their stomachs (Noble and Noble, 1923). Captive specimens fed on crickets and flies (Bullard, 1965) and moths and mealworms (Means and Longden, 1976).
O. Predators. Potential tadpole predators found in Pine Barrens treefrog larval habitats included adult bronze frogs (Rana c. clamitans), two-toed amphiumas (Amphiuma means), red salamanders (Pseudotriton ruber), and banded pigmy sunfish (Elassoma zonatum; Means and Longden, 1976). Also, painted turtles (Chrysemys picta), spotted turtles (Clemmys guttata), and common snapping turtles (Chelydra serpentina) may be tadpole predators wherever their geographic distributions overlap with that of Pine Barrens treefrogs (Wright, 1923). Aquatic predaceous insects, mudminnows (Umbra pygmea), banded sunfish (Enneacanthus sp.), and pickerels (Esox sp.) were presumed to be major predators in New Jersey (Wright, 1923; Freda and Morin, 1984). The only documented predators of adult Pine Barrens treefrogs are banded water snakes (Nerodia sipedon; Kauffeld, 1957) and ribbon snakes (Thamnophis sauritus; Freda and Gonzalez, 1986).
P. Anti-Predator Mechanisms. When frightened, adult frogs “invariably leap to the ground and, with a series of short jumps, disappear among the grass and sphagnum of the bog” (Noble and Noble, 1923). No other anti-predator mechanisms are known.
Q. Diseases. Unknown.
R. Parasites. Unknown.
4. Conservation. Pine barrens treefrogs are considered Endangered by the State of New Jersey (New Jersey Natural Heritage Program, 1995), Significantly Rare in North Carolina (LeGrand and Hall, 1999), Threatened in South Carolina (Garton and Sill, 1979), and have no status in Georgia. Based upon existing information in the early 1970s, Florida populations were listed as Endangered by the U.S. Fish and Wildlife Service (Federal Register, 1977, 42(218):58754-58756), but over time, knowledge about the Florida/Alabama distribution of Pine Barrens treefrogs has steadily increased (Means and Longden, 1976; Means and Moler, 1979; Mount, 1980; Moler, 1981; Jensen, 1991; Printiss and Hipes, 1999). This has led to delisting the species at the federal level, so that Pine Barrens treefrogs are now considered Rare by the State of Florida (Means, 1992a), where > 135 localities are known, with many on publicly owned lands (Moler, 1981; Printiss and Hipes, 1999). About 20 localities are known from Alabama, where the species is considered Threatened (Means, 1986a). Conservation of Pine Barrens treefrogs depends upon the long-term existence of suitable breeding and adult habitat in all three enclaves.
Freda and Morin (1984) pointed out that the seepage waters where Pine Barrens treefrogs breed and develop are some of the most acidic, dilute, and nutrient-deprived freshwater ecosystems in North America. Pine barrens treefrogs have specific physiological, behavioral, and biochemical adaptations to survive in such demanding aquatic environments. Any perturbations of the water chemistry of herb bogs and shrub bogs, caused for example by agricultural and residential development upstream, upslope, or in the preferred habitats, would probably have dramatic negative impacts on Pine Barrens treefrogs. Also, changes in groundwater chemistry or activities that lower the water table would be highly detrimental because they would pollute the breeding habitat or cause the drying of bogs. Liming of ponds and food plots within wildlife management areas, for example, should be prohibited.
Having populations on publicly owned lands, however, is in itself not sufficient to ensure the survival of the species. Active management must be undertaken to maintain a certain level of quality of the preferred habitat of Pine Barrens treefrogs. Next to assuring an adequate high-quality water supply in breeding habitats, the most important management actions are to periodically set back plant succession in herb bogs. Lightning-ignited fires that ran downslope from longleaf pine forests through herb bogs and then into shrub bogs were once the natural agency that kept streambottom hardwood trees out of shrub bogs and evergreen shrubs out of herb bogs (Means and Moler, 1979). Plant succession was thus set back by frequent fires. Because natural wildfires are no longer a feature of southeastern U.S. landscapes, management of Pine Barrens treefrog habitat must be accomplished by controlled burns or prescribed fires.
1D. Bruce Means
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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