Amphibians of North Carolina
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NC Records

Lithobates palustris - Pickerel Frog



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Taxonomy
Class: Amphibia Order: Anura Family: Ranidae Synonym: Rana palustris
Taxonomic Comments: Frost et al. (2006) placed species in North American that were formerly in the very large genus Rana into a separate genus, Lithobates, to distinguish them from a large and predominantly Eurasian genus Rana (sensu stricto). There have been numerous arguments put forth for well over a decade about whether these species should be placed back into Rana or retained as Lithobates, with some supporting placing Lithobates as a subgroup within Rana and others supporting the recognition of both genera. There has been no clear resolution of the issue, and both Lithobates and Rana continue to be widely used in recent published literature on North American species. Here, we follow the recommendations of the Society for the Study of Amphibians and Reptiles' Standard English Names Committee and use Lithobates for North American representatives of this group.
Species Comments:
Identification
Description: Adult Lithobates palustris are medium to large frogs with a pointed snout and an olive green to brownish ground color. A conspicuous light to cream-colored dorsolateral fold extends down each side of the body from behind the eye to the groin region. A series of large dark brown blotches (typically 10-16) are present between the dorsolateral folds that are arranged in two rows. The blotches are often narrowly margined with cream-coloration and can assume various irregular shapes. These range from highly elongate to roughly elliptic, oval, rectangular or squarish. A third row of large blotches is present on the side of the body immediately below the dorsolateral fold, along with a series of progressively smaller blotches towards the juncture with the belly. The skin on the dorsum is mostly smooth, but there are often two or more raised ridges of variable lengths between the dorsolateral folds that tend to be centered on the dorsal spots. The dorsum of the rear limbs usually have a series of dark bands, but these are sometimes replaced by blotches. The undersides are typically white except for a conspicuous yellowish to orange wash in the groin region and on the underside of the hind limbs. A whitish to cream-colored line is present on each side that extends from near the nares rearward along the upper jaw before ending below and just beyond the tympanum.

Sexually mature males have paired vocal sacs and enlarged thumbs with thickened pads that are used to amplex females. Adult males in local and regional populations are typically 10-20% smaller than the females based on SUL (Dodd 2013). Males become sexually mature when 41 mm SUL or larger, and females when 46 mm SUL or larger. Some specific size ranges based on SUL as summarized by Dodd (2013) include 45–58 mm for males and 60–76 mm for females in Ohio, 41–58 mm (mean = 50 mm) for males and 51–79 mm (mean = 61 mm) for females in Connecticut, and 42-65 mm (mean = 53 mm) for males and 48-75 mm (mean = 64 mm) for females in Louisiana. Other reports include 45–61 mm for males and 59–86 mm for females in Missouri (Resetarits and Aldridge 1988) and 41-67 mm for males and 57-87 mm for females in Pennsylvania (Meshaka et al. 2012a).

The older tadpoles can grow to 76 mm TL and are large, deep, and full-bodied with an olive green ground color that grades to yellow on the sides (Dodd 2013). The belly is cream colored and the dorsum is marked with fine black and yellow spots. The tail is similar in coloration to the body, with faint cream and darker speckling on the fins. Dodd (2013) noted that the tadpoles of this species are difficult to distinguish from those of several other ranids of similar size such as those of L. clamitans and L. catesbeianus.

In North Carolina, juveniles and adults in the Coastal Plain often have bellies that are mottled with brown, along with dorsal blotches that merge into more elongated bars or stripes (Beane et al. 2010). These forms were once described as a separate subspecies (L. palustris mansuetii) but it is no longer recognized by taxonomists since morphs of this type have been found in other areas of the range.
Vocalizations: The males produce several types of vocalizations, including an advertisement call and two additional calls associated with aggressive interactions with other males (Given 2005). The advertisement call has been likened to a continuous low-pitched snore. Each call lasts for 1-2 seconds and tends to be most intense near the middle of the call. Individuals normally pause for 5-10 seconds before issuing another call. Given (2005) found that the duration of the call tends to increase with body size, which may allow females to discrimination between individuals based on male size.

Given (2005) recognized two types of aggressive calls that were a very brief “snicker” that lasted for about one-fourth of a second, and a more prolonged “growl” that lasted for a second or two. These both have dominant frequencies that are lower than that of the advertisement call, and were issued in combination when a playback advertisement call was made next to a territorial male. They presumably serve to warn intruders of trespass and the likelihood of having physical encounters with territorial males.

The males will call from both above and below the water surface. Individuals that are calling from the surface will often dive below water if disturbed and continue calling (Dodd 2013, Given 2008). They typically return to the surface after a few minutes and resume issuing advertisement calls. Given (2005) found that playback calls could trigger males to move beneath water and issue all three types of calls.
Technical Reference: Dodd (2013)
Online Photos:    Google
Observation Methods: The juveniles and adults are sometimes encountered while crossing roads on rainy nights, while the calling males can be heard during the spring warm-up and early summer. Individuals are occasionally flushed when walking along the margins of woodland streams.
AmphibiaWeb Account
Distribution in North Carolina
Distribution Comments: The Pickerel Frog is broadly distributed throughout eastern North America from southeastern Canada south and southwestward to eastern Texas and a small portion of the Gulf Coast. This species is unevenly distributed in the eastern US, with populations apparently missing from regional areas such as much of Illinois and portions of western Tennessee. The western limit of the range generally corresponds to the Eastern Deciduous Forest and ends in eastern Texas, eastern Oklahoma, and comparable areas farther north to Wisconsin and northern Michigan. In North Carolina, populations tends to be patchily distributed in some areas of the state. They are most common in the Piedmont, and rather poorly represented in the southern mountains and the Coastal Plain where suitable habitats are less common (Beane et al. 2010).
Distribution Reference: Beane et al. (2010), Dodd (2013)
County Map: Clicking on a county returns the records for the species in that county.
Key Habitat Requirements
Habitat: The Pickerel Frog is generally associated with forested landscapes with appropriate breeding sites, but can also be found in areas with a mosaic of forested and non-forested patches such as meadows or agricultural fields. The juveniles and adults tend to seek out cool microhabitats after moving from the breeding sites and can be found in mesic and bottomland forests, moist meadows and marshes, sphagnum bogs, cool ravines, and along cold streams and rivers (Dodd 2013). Southern populations are often found in bottomland forests, swamp forests, or in steep, shaded ravines. This species is regularly found in caves or near cave entrances in karst regions where they use these as overwinter sites and thermal refugia. Fenoilio et al. (2005), for example, observed a seasonal peak count of 53 individuals in November in a cave in the Ozarks, while Resetarits (1986) estimated a cave in Missouri to contain at least 365 overwintering individuals.

Lithobates palustris normally breeds in semipermanent or permanent wetlands (e.g., Babbitt et al. 2003, Herrmann et al. 2005) and will often use large bodies of water such as ponds and larger lakes. They also use a variety of other natural and artificial breeding habitats, including beaver ponds, marshes, isolated Coastal Plain wetlands (Russell et al. 2002a), small reservoirs, retention ponds, farm ponds, rock quarries and sand pits (Dodd 2013). They use both fish-free habitats and permanent habitats with fish (Baber et al. 2004, Hecnar 1997, Hecnar and M’Closkey 1997b). The breeding sites often have shallow zones with emergent vegetation and a partial to complete canopy cover. In addition to standing water habitats, the adults occasionally breed in pools in spring-fed streams and other cold habitats. Wright (1914) reported them using cold streams and the plunge pools of waterfalls in New York, while Holomuzki (1995) found them in a second-order section of a Kentucky stream where fish densities were low.

In North Carolina, specimens have been found in a variety of wet to mesic habitats that include wet pastures, freshwater marshes and marshy sloughs, bogs, mesic and bottomland forests, cypress swamps, woodland and floodplain pools, farm ponds, quarry ponds, fish hatchery ponds, the vegetated margins of reservoirs, and along the banks of woodland streams and larger rivers.
Environmental and Physiological Tolerances: Lithobates palustris is not highly acid-tolerant, with the critical pH for the eggs and larvae being between 4.3 and 4.5 (Dodd 2013, Gosner and Black 1957a).
Biotic Relationships: The eggs and larvae can be found in both running and standing water habitats and are exposed to numerous aquatic predators. Eastern Newts (Notophthalmus viridescens) will eat the eggs (Wright 1914) and the larvae are undoubtedly taken by numerous aquatic predators, including odonates and Eastern Newts (Wilbur and Fauth 1990). Holomuzki (1995) studied a stream-breeding population in Kentucky and found that the larvae appear to have limited chemical defenses against one sunfish (Lepomis megalotis), but not a second (L. cyanellus). The tadpoles reduced their activity levels when exposed to chemical cues from Lepomis megalotis, and minimized predation risk by remaining in very shallow water near the stream edge.

The juveniles and adults produce noxious skin secretions along the dorsolateral fold that may partially deter certain predators (Dodd 2013). Herpetologists have long noted that if other amphibians are placed in a collection bag with a Pickerel Frog that they may die or show signs of distress, which suggests that the skin secretions are also toxic to some organisms. Pickerel Frogs have a distinctive odor to humans that may help to warn potential predators of their distastefulness. The yellowish-orange coloration of the legs and groin may serve as aposematic (warning) coloration, but this has yet to be demonstrated (Dodd 2013). When attacked, individuals may inflate the body and tilt the head downward while facing the attacker. This functions to make the frog appear larger than it is and orient the granular glands in the predator’s direction. Other defenses against predators include crypsis coupled with remaining motionless, fleeing, and crouching and hiding (Dodd 2013, Formanowicz and Brodie 1979, Marchisin and Anderson 1978).

Despite having chemical and behavioral defenses, the juveniles and adults are preyed upon by other vertebrates. The documented predators include American Bullfrogs, Green Frogs, pike (Esox), the Common Watersnake (Nerodia sipedon) and mink. There is also one record of predation by a Bald Eagle (Dodd 2013). Gartersnakes (Thamnophis sirtalis; T. sauritus) will sometimes reject Pickerel Frogs (Babbitt 1937, Dunn 1935, Walker 1946) as will the Common Watersnake (Nerodia sipedon) and shrews (Blarina; Babbitt 1937, Formanowicz and Brodie 1979).

See also Habitat Account for General Waters and Shorelines
Life History and Autecology
Breeding and Courtship: Breeding in local populations can occur from winter through early summer depending on the latitude and local site conditions. Males in the southern portion of the range may begin calling as early as December-February (Dundee and Rossman 1989, Garrett and Barker 1987, Hardy and Raymond 1991, Mount 1975), while those in the northern US and Canada may not begin until late April or May (e.g., Babbitt 1937, Dodd 2013, Oliver and Bailey 1939, Wright 1914). In North Carolina, calling typically begins in mid-February or later and last for around 4-6 weeks in local populations (Murphy 1963, Todd et al. 2003). Hocking et al. (2008) found that males and females tended to arrive at the same time, which suggests that the breeding season roughly parallels the calling season. Wright (1914) noted that the egg-laying period typically last for only three weeks in New York for any given site and year. However, it varies substantially across years and sites so that the entire breeding season extends for around six weeks.

The adults undertake seasonal migrations to and from the breeding sites. The breeding season for this species is prolonged, with the adults arriving and departing in small numbers over the course of several weeks. Hocking et al. (2008) monitored several ponds in Missouri with drift fences and found that the adults immigrated from mid-March through mid-May, with a peak about three weeks after immigration began. Movement away from the ponds began in early April and was completed by late May. Given (2005) estimated the breeding season to last around five weeks at a Delaware site based on sustained choruses, with very limited calling after that for another two weeks.

After arriving at the breeding sites the males set up calling sites that are often in close proximity to other males. Chorusing is most concentrated during the first 4-5 hours after dark in North Carolina and elsewhere, although some individuals will call until dawn (Given 2005, Todd et al. 2003). Individuals will also call sporadically during the day. Given (2005) conducted a detailed study of a population in Delaware and found that most males stayed and called throughout the entire breeding season (median duration = 25 nights). They established small territories and advertised and defended these using advertisement and aggressive calls. Individuals occasionally engaged in wrestling matches to settle disputes. Calling is energetically expensive and most males lost weight as the calling season progressed, with larger males losing proportionately more weight than smaller males.

Wright (1914) reported that males in New York often concentrated locally in shallow water where groups of amplexed pairs and ovipositing females were present. In one area that was < 0.3 meters square he observed 21 unmated males, 5 amplexed pairs, and eight fresh egg masses. Females typically remain for a much shorter duration at the breeding sites than the males and operational sex ratios are skewed towards males. Murphy (1963) estimated a sex ratio of 6.6 males per female over the breeding season at a pond in North Carolina, while Hardy and Raymond (1991) estimated ratios of 1.3 and 5.4 males per female during different years at a site in Louisiana. Ratios at two sites in Wisconsin were 2.4 and 3.0 males per female (Johnson 1984).

Mate choice by females has not been studied in detail and it is uncertain if they use the vocal characteristics of males to select mates. Wright (1914) observed dense concentrations of males locally in New York, which suggests that males at some sites may engage in scramble competition and grab any female that approaches. He observed several instances in which males attempted to dislodge amplexed males. Amplexus in this species is pectoral and apparently prolonged, at least in New York. Wright (1914) noted that pairs may remain amplexed for 2-5 days before laying eggs. He often observed amplexed pairs on land near the breeding sites and assumed that amplexus occurred in water before the pairs moved onto land. Egg laying can occur anytime during the day or night.
Reproductive Mode: Each female lays a single globular to somewhat oblong egg mass that is commonly around 8-10 cm in diameter when fully swollen. The size of 14 egg masses from Wisconsin measured by Johnson (1984) varied from 5.0-14 cm (mean = 8.8 cm) by 5.0-13 cm (mean = 8.1 cm). Females typically attach their egg masses to submerged branches, sticks, plant stems or other support structures. The egg masses are often laid in shallow water in relatively sunny locations, but are sometimes placed in deeper water up to a meter below the surface (Johnson 1984, Wright 1914). Females that bred in a stream in Kentucky deposited their masses in deep water in pools that were relatively permanent (Holomuzki 1995).

When laying eggs, a female will grasps a stick or other support structure with her hind legs and flatten her body so that it is horizontal. The male positions his hind limbs parallel to those of the female, then fertilizes the eggs as they are extruded. The entire process takes around 3 minutes, and the pair departs immediately thereafter (Wright 1914). The freshly laid eggs are brown above and yellowish below and are surrounded by two jelly envelopes. Eggs from New York that were measured by Wright (1914) averaged from 1.7-1.9 mm in diameter (range = 1.6-1.9 mm) and the outer envelope averaged 4.0 mm (range = 3.6-5.0 mm). Developing embryos that were tracked in natural breeding sites required 11-21 days to reach the hatching stages. Embryos in southern populations likely develop faster, but data are lacking.

Data for average clutch sizes are surprisingly similar in many areas of the range. Resetarits and Aldridge (1988) reported an average of 1,759 ovarian eggs (range = 704-2896) for 33 females from a cave site in Missouri, while Trauth et al. (1990) found an average of 1,760 ova (range = 960-2,943) in 14 Arkansas females. Ten females from Pennsylvania contained an average of 1,785 ovarian eggs (range = 850-2450; Meshaka et al. 2012). In all three of these studies, clutch size increased significantly with female SUL. Others have reported a range of 780–1,834 ova in Nova Scotia specimens (Gilhen 1984), an average of 2,652 eggs for Kentucky specimens (Westerman et al. 2003), and 1,413 eggs for a single egg mass from Virginia (Mitchell and Pague 2014).
Aquatic Life History: The tadpoles appear to filter-feed on muddy substrates and consume diatoms, blue-green algae, and both filamentous and non-filamentous green algae (Dodd 2013). The larvae are capable of rapid growth and can reach 60-70 mm TL within a few months after hatching. Growth rates are presumably dependent on ambient conditions such as food levels, water temperatures, and the densities of predators and competitors, but almost no information is available from natural breeding sites.

The larval period appears to last only 2-5 months in most populations. Based on their analyses of museum specimens, Meshaka et al. (2012) estimated the larval period to last 2-3 months in Pennsylvania, with metamorphs appearing in June through August. Wright (1914) estimated a larval period of 90–100 days or more in New York populations, while Hocking et al. (2008) estimated a minimum and maximum larval period of 125 to 157 days in Missouri based on drift fence captures. In the extreme northern portions of the range larvae may overwinter and transform the following July or August (Bleakney 1952). Meshaka et al. (2012) reported young metamorphs in Pennsylvania to vary from 19-32 mm SUL (mean = 26 mm) based on museum specimens. Other reported values for size at metamorphosis as summarized by Dodd (2013) include 25–28 mm SUL in New York, 19–27 mm SUL in the Great Smoky Mountains, 19–26 mm SUL in Ohio, and 25–29 mm SUL in Nova Scotia.
Terrestrial Life History: The ecology of the young metamorphs and juveniles is poorly documented. The metamorphs begin dispersing away from the breeding sites within a few weeks after metamorphosing (Hocking et al. 2008), but information on the distances that they move, use of dispersal corridors, and microhabitat use are lacking. Both the juveniles and adults tend to emigrate during rainy weather (Murphy 1963). Adults that were tracked in Wisconsin by Johnson (1984) were sedentary during the summer months and remained in very close vicinity to spring-fed streams where they frequented bank overhangs and root tangles.

Based on analyses of museum specimens, Meshaka et al. (2012) concluded that metamorphs in Pennsylvania emerge in June through August when 19-32 mm SVL (mean = 26 mm). The males became sexually mature the following spring around 10 months after metamorphosing, while females reached sexual maturity the following summer at approximately 13 months post-metamorphic age. They begin yolking their first clutch shortly thereafter and breed for the first time the following year, approximately 22-23 months after transforming.

The juveniles and adults are active during the warmer months of the year, and can have extensive overwintering periods in the northern portions of the range. In Pennsylvania, for example, individuals are active from March through November, with most becoming surface inactive in October (Meshaka et al. 2012). Overwintering occurs in a variety of sites that provide protection from freezing. Commonly used sites include springs and seeps, muddy pond bottoms, protected ravines, and areas in or near caves (Dodd 2013).

The juveniles and adults appear to be opportunistic, gape-limited predators that will take a wide variety of palatable prey, with insects forming the bulk of the diet. Dodd (2013) summarized the major dietary studies and listed the known prey groups. These include ants, true bugs, beetles, sawfly larvae, adult and larval moths, adult and larval flies, damselflies, crickets, aquatic and terrestrial beetles, wasps, springtails, sowbugs, earthworms, snails, slugs, spiders, centipedes, harvestmen, pseudoscorpions and mites.
General Ecology
Population Ecology: We know very little about local population sizes or population structure for this species. The Pickerel Frog tends to be spottily distributed in many areas of its range. It is often underrepresented in occupancy surveys and is considered uncommon or rare in many areas (Dodd 2013). Many seemingly good habitats lack breeding populations for reasons that are not fully understood. We have very little data on the dispersal distances and movements of the juveniles and adults. The extent to which local and regional populations are interconnected and show evidence of metapopulation structure needs study.
Community Ecology: The tadpoles usually share breeding sites with potential competitors and predators, but interactions between these groups are poorly researched. Wilbur and Fauth (1990) examined community interactions of two predators (Eastern Newt; Anax dragonfly) with two combinations of prey (Anaxyrus americanus; L. palustris) in experimental tanks. Under these conditions, Pickerel Frog tadpoles suffered greater mortality from odonate larvae than newts, and competed with toad tadpoles in the absence of these predators. The predators reduced the densities of tadpoles in the tanks and mediated both intra- and interspecific growth responses that were presumably due to competition for limited food resources.
Adverse Environmental Impacts
Status in North Carolina
NHP State Rank: S5
Global Rank: S5
Environmental Threats: The Pickerel Frog is spottily distributed throughout much of its range, but it is uncertain whether this reflects a natural pattern or long-term anthropogenic losses (Dodd 2013). Populations appear to have declined in some areas such as Kansas where the species was last reported in 1934. This species tends to avoid open areas such as pastures or grassy road corridors when dispersing and favors forested habitats and stream corridors (Gibbs 1998a). Areas with urban development, fragmented landscapes, and high road densities provide poor habitats for local populations.
Status Comments: This species appears to be relatively common in North Carolina compared to many areas of the range. There is no evidence of significant population declines in recent years.
Stewardship: Populations are best maintained by having a series of local semipermanent or permanent wetlands that are interspersed in a forested matrix. Wooded stream corridors appear to be important landscape features that are used during dispersal and migration to and from breeding sites and should be protected to maintain connectivity between local pond populations.

Recording Gallery for Lithobates palustris - Pickerel Frog

2022-03-07. Orange Co. Steve Hall - Several males heard singing within a larger chorus of Southern Leopard Frogs. Located around the edge of a marshy slough. Between 2100 and 2200 following a heavy downpour. ~64 F.

Photo Gallery for Lithobates palustris - Pickerel Frog

13 photos are shown.

Recorded by: Carol Ann McCormick
Alamance Co.
Recorded by: K. Bischof
Transylvania Co.
Recorded by: tom ward
Buncombe Co.
Comment: A metamorphosing individual that has a ways to go.
Recorded by: H. Quay
Durham Co.
Recorded by: John Petranka
Wilkes Co.
Recorded by: tom ward
Buncombe Co.
Recorded by: tom ward
Buncombe Co.
Recorded by: A. Lasley
Burke Co.
Recorded by: Owen McConnell
Granville Co.
Recorded by: Pat Momich
Madison Co.
Recorded by: John Petranka
Durham Co.
Recorded by: Steve Hall
Montgomery Co.
Recorded by: Owen McConnell
Durham Co.