Amphibians of North Carolina
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NC Records

Pseudacris ocularis - Little Grass Frog


Taxonomy
Class: Amphibia Order: Anura Family: Hylidae Subfamily: Hylinae
Taxonomic Comments: Pseudacris ocularis has been placed in several genera over the years, including Hyla and Limnaeodus, but more recent molecular studies place it with other Pseudacris species (e.g., Moriarty and Cannatella 2004).
Species Comments:
Identification
Description: Adults of the Little Grass Frog are tiny frogs with smooth skin, a pointed snout, and moderately developed toe pads. They are the smallest terrestrial vertebrate in the United States, with the adults varying from 10-20 mm SUL. The dorsal ground color can be various shades of gray, greenish, brown, bronze, or reddish (Dodd 2013). The back is frequently unmarked, but some specimens may have a rather faint dark band or elongated blotch down the middle of the back. A similar mark may occur dorsolaterally on the posterior half of the body. The most conspicuous mark is a thick, dark line or band on each side that runs from near the nostril rearward through the eyes where it broadens before reaching the shoulder region. From there it usually continues as a somewhat narrowing band to the groin. A thin whitish line is also often present below this that extends from the upper lip toward the shoulder. A black line is usually present along the back of each lower leg, and the venter is yellowish white and unmarked.

The males in local populations average slightly smaller than the females, and have a dark throat during the breeding season. Males that were collected by Wright (1932) in southeastern Georgia varied from 11.5–13.5 mm SUL versus 12–17.5 mm SUL for females. In southern Florida, males examined by Duellman and Schwartz (1958) averaged 14.2 mm SUL (range = 13.0-15.5; n = 20) versus 15.6 mm SUL (range = 15.3-16.0; n = 4) for females. Beane et al. (2010) reported a size range of 13-20 mm SUL for adults in the Carolinas and Virginia.

The mature tadpole has a drab brown or olive-green ground color with scattered black spots on the dorsum. The tail musculature has a dark stripe on the upper half and a contrasting parallel ventral light stripe on the lower half (Dodd 2013). A light stripe also extends forward to the eye from the tail musculature and is paralleled by a darker stripe beneath it. The throat and chest are mottled. The tail fins can be clear or contain a series of blotches along the margins (Gregoire 2005). The dorsal tail fin is higher than the ventral fin and the tail tip is sharply acuminate. The mature tadpoles can reach 23 to 25 mm TL.

Adults of the Little Grass Frog can be confused with juveniles of P. nigrita and P. brimleyi, but the latter have granular skin rather than smooth skin as seen in P. ocularis. In addition, adult P. ocularis of similar size can be identified either by the dark throat of males or the presence of eggs that are visible through the body wall (Beane et al. 2010).
Vocalizations: The call of P. ocularis is a faint, very high-pitched, repetitive insect-like “ts-r-e-ek” or “s’lick” that Harper (1939b) described as resembling tinkling beads. Blair (1958a) noted that the dominant frequency is around 7,125 cps which may be difficult for some humans to hear. Field observations by Harper (1939b) indicate that the call sequences are variable, but individual males will often produce 8-15 repetitive calls (tinkles) in a row before pausing. Call rates are temperature dependent, but each call lasts about a half to three-quarters of a second, and often with somewhat unequal intervals between them. Wright (1932) found that individuals in natural habitats in Georgia made from 20-61 calls per minute, with an average of around 32. He noted that the calls can be heard as far as 45-60 m away.
Technical Reference: Dodd (2013)
Online Photos:    Google
Observation Methods: The adults are most easily observed by finding calling males as the breeding sites or searching grassy vegetation around pond and swamp margins during the day or night.
AmphibiaWeb Account
Distribution in North Carolina
Distribution Comments: The range extends along the Atlantic Coastal Plain from southeastern Virginia southward to southern Florida, and from southeastern Georgia westward to extreme southwestern Georgia, the eastern Panhandle of Florida, and extreme southeastern Alabama (Houston County). In North Carolina, populations occur throughout much of the Coastal Plain. They also can be found on the Outer Banks, including Roanoke Island and Smith Island (Gaul and Mitchell 2007, Gibbons and Coker 1978). This species is most common in the pine flatwoods of the lower Coastal Plain.
Distribution Reference: Beane (2010), Dodd (2013)
County Map: Clicking on a county returns the records for the species in that county.
Key Habitat Requirements
Habitat: The Little Grass Frog appears to rarely move far from its breeding sites, although it is possible that individuals leave very shallow seasonal ponds that dry and become inhospitable. They can be found in a variety of moist habitats in or near grassy or vegetated shallows. The breeding sites are most commonly temporary and semipermanent wetlands, and both natural and artificial habitats are used for breeding and as habitats for the terrestrial stages. These can be embedded in a variety of upland settings such as sandhills, flatwoods, and mixed pine-deciduous forests, as well as disturbed habitats such as cut-over woods, powerline right-of-ways, and agricultural and silvicultural lands.

Dodd (2013) summarized many of the numerous habitats that have been reported in the published literature. These include low wet pine flatwoods, sand pine plantations, xeric hammocks, dome swamps, river hammocks, creek swamps, wet prairies, cypress savannas, cypress and gum ponds and bays, sphagnum bogs, drainage and roadside ditches, and depression and basin marshes. Both open and closed canopy sites are used, but open canopy sites appear to be preferred (Dodd 2013).

Populations in North Carolina use similar aquatic habitats that typically have vegetated shallows with grasses or other vegetative cover. They have been found in roadside ditches, drainage ditches in agricultural settings, borrow pits, Carolina bays, grassy pools associated with swamp complexes, and both seasonal and permanent ponds.
Adaptations to Natural Disturbances: Schurbon and Fauth (2003) found that P. ocularis appears to tolerate prescribed burns of different yearly intervals reasonably well in South Carolina. This implies that this species was probably well-adapted to tolerating natural fires that prevailed centuries ago.
Biotic Relationships: The natural predators of the tadpoles and terrestrial stages are poorly documented but undoubtedly include numerous aquatic and semiaquatic predators. This species is small enough to be taken by spiders (Nyffeler and Altig 2020), and Fogarty and Hetrick (1973) reported that Cattle Egrets consumed two adults.
See also Habitat Account for Coastal Plain Sedge, Grass, and Rush Mires
Life History and Autecology
Breeding and Courtship: Calling and breeding can occur year-round in Florida and Georgia (Babbitt and Tanner 2000, Carr 1940a, Dodd 2013, Harper 1939b), although Jensen et al. (2008) reported that breeding only occurs from January to September in Georgia. In the northern part of the range most breeding occurs during the winter and spring months, particularly from March to April (Dodd 2013). Calling may begin in February in North Carolina and extend through September.

The males prefer shallow sites with grasses, sedges, and rushes for calling, but rarely call while directly sitting or floating in water. Harper (1939) noted that the males may perch as high as a meter or so on shrubs or tree trunks, but more commonly call close to the water's surface while sitting or perched on grasses and sedges, sticks, or mats of detritus. Calling occurs at temperatures >10°C, but especially at 21–26°C, and large choruses are often heard after heavy rains (Dodd 2013, Wright 1932). Females presumably begin laying shortly after the male engages in axillary amplexus (Wright 1932).
Reproductive Mode: Females typically lay their eggs singly and may attach them to sticks or other support structures (Wright 1932). The freshly laid eggs are brown above, cream-colored below and are surrounded by a single jelly envelope. Eggs that were observed by Wright (1932) from Georgia were 0.6–0.8 mm in diameter (mean = 0.75 mm) with envelopes that were 1.2–1.8 mm in diameter (mean = 1.36 mm), while those observed by Gosner and Rossman (1960) from northern Florida ranged from 0.88 to 1.03 mm (mean = 0.95 mm) and had envelopes that were 1.5-1.68 mm (mean = 1.57 mm). The envelope is sticky and adheres to debris, and the embryos typically hatch in 2-4 days when around 3.5 mm TL (Dodd 2013, Gosner and Rossman 1960).

Clutch sizes are poorly documented, but females are thought to lay around 100-200 eggs (Dodd 2013). A single captive female from Virginia laid 116 eggs (Mitchell and Pague 2014).
Aquatic Life History: Most aspects of the larval ecology are poorly documented. Dodd (2013) noted that the tadpoles graze on algae and aquatic vegetation. Kehr (1997) found that larvae at a Florida site moved from deeper areas to the shallow, warm pond margins during the day. He reported that the mean length of the larval period was only 7.3 days based on a software analysis, but his actual field data (Table 1) show that no larvae had metamorphosed after nearly a month of growth. Gosner and Rossman (1960) reported a larval period of 42 days under laboratory conditions. This very limited data set suggests that a month or more is required for larvae to complete the larval stage. The mature tadpoles can reach 23 to 25 mm TL (Dodd 2013), but recently metamorphosed froglets are only 7–9 mm SUL (Gosner and Rossman 1960, Marshall and Camp 1995, Wright 1932).
Terrestrial Life History: Individuals normally do not stray far from its breeding sites and resides year-round in shallow grassy wetlands such as cypress domes or marshes. However, Dodd (1996) reported a single individual 434 m from the nearest water in a sandhills habitat in northern Florida. The adults are commonly found in vegetated areas in or along the margins of wetlands and frequently perch of woody stems or the boles of small trees, particularly when calling. Individuals presumably move beneath surface cover or other refuges during droughts or bouts of cold winter weather, but very little is known about this and many other aspects of the life history.

They juveniles and adults appear to be generalist predators that feed on small arthropods. Marshall and Camp (1995) examined 50 individuals from two populations in Georgia and found that about 50% of the prey items consisted of collembolans (springtails). Other prey included ants, parasitic wasps, plant hoppers, beetles, mites, and several miscellaneous taxa. The young metamorphs consumed a wider variety of prey than the adults, and the prey of both groups were predominantly species that are associated with soil or leaf litter.

Individuals that metamorphose in the summer likely become sexual maturity by the the following spring. As noted by Dodd (2013) remarkably little is known about the demography or longevity of this species.
General Ecology
Population Ecology: Very little is known about the population biology of this species. Local populations probably consist of a few dozen to many hundreds of adults. Some of the older accounts (Harper 1939b, Wright 1932) described very large choruses after heavy rains. Monitoring of local population sizes is difficult since this species does not undergo seasonal migrations to the ponds and can likely trespass across drift fences. We also lack basic information on dispersal and movements of individuals between local populations. Individuals in local populations appear to show high site fidelity, but much more information is needed on dispersal and connectivity at different spatial scales.
Community Ecology: Little Grass Frog often shares breeding sites with other anurans and an array of predators, but interactions with other community members are undocumented.
Adverse Environmental Impacts
Habitat Loss: Populations are threatened by habitat loss and urbanization. Guzy et al. (2012), for example, found that P. ocularis and several other anurans were commonly encountered in healthy cypress dome wetlands in the Tampa Bay region of southwestern Florida, but were missing from degraded cypress dome sites in urbanized areas. Populations can adapt to moderate habitat disturbances such as those associated with timbering or the conversion of land to improved pastures, but are less tolerant of urbanization and the conversion of land to agricultural fields (Babbitt and Tanner 2000, Delis et al. 1996, Dodd 2013).

Status in North Carolina
NHP State Rank: S5
Global Rank: G5
Environmental Threats: Populations are threatened by habitat loss and urbanization. The continued loss of seasonal wetlands is a significant concern, but the use of roadside ditches and other artificial habitats has helped to offset losses of natural habitats.
Status Comments: Populations in North Carolina show no evidence of widespread declines in recent decades and appear to be stable.
Stewardship: Populations are best maintained by protecting seasonal and semipermanent wetlands.

Photo Gallery for Pseudacris ocularis - Little Grass Frog

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Recorded by: Mark Shields
Onslow Co.