Amphibians of North Carolina
Scientific Name:
Common Name:
 Family (Alpha):
»
Sirenidae Members:
NC Records

Siren intermedia - Lesser Siren

Taxonomy
Class: Amphibia Order: Caudata Family: Sirenidae
Taxonomic Comments: Populations that have been assigned to Siren intermedia constitute a geographically variable group. They extend from Virginia mostly along the Coastal Plain to as far south as southern Texas and Mexico, and as far north as Michigan. Three subspecies have been recognized in the past (Martof 1973, Petranka 1998). The Rio Grande Siren (S. i. texana) is a relatively large subspecies that reaches 69 cm TL and is restricted to the lower Rio Grande Valley and adjoining regions in northern Mexico. The Western Lesser Siren (S. i. nettingi) only grows to 50 cm TL, has a modal number of 35 costal grooves, and is found from Alabama westward to central Texas and northward through the Mississippi Valley to Michigan. The Eastern Lesser Siren (S. i. intermedia) reaches a maximum length of only 38 cm, has a modal number of 32-33 costal grooves, and occurs from central Alabama to southeastern Virginia. Recent studies suggest that S. intermedia consists of several genetically distinct groups that may warrant recognition as new species. The populations in south Texas and Mexico are problematic (LaFortune 2015) and others along the Gulf Coast warrant more careful study (Graham et al. 2018). Many authorities no longer recognized the Rio Grande Siren as a valid subspecies. The remaining two continue to be recognized, including the Eastern Lesser Siren that occurs in North Carolina.
Species Comments:
Identification
Description: The Lesser Siren is a large, elongated, eel-like salamander that lacks rear limbs and has four toes on each front limb. The head is flattened and a set of bushy gills on the sides of the head help to distinguish this species from amphiumas, which are superficially similar. Adults reach a maximum size of around 69 cm TL -- but are typically much smaller in most populations -- including those in North Carolina (Beane et al. 2010). The margins of the jaws are covered with a horny sheath, and a narrow dorsal fin extends from the vent to the tail tip. The dorsal ground color of adults varies from olive green to grayish blue or black. Lighter colored individuals often have numerous scattered brown or black dots on the dorsum. The venter is slightly lighter than the dorsum, and white to yellowish flecks are sometimes present along the sides of the body in some populations (Martof 1973). Males average slightly larger than the females in many populations and have enlarged masseter muscles that cause the temporal region of the head to appear swollen (Petranka 1998).

The Eastern Lesser Siren (S. i. intermedia) occurs in North Carolina. This subspecies has fine black dots scattered over the dorsum and tail, a uniformly colored venter that lacks light spots, and 31-35 costal grooves between the front limbs and the cloaca. The Eastern Lesser Siren is a relatively small subspecies, with the adults in North Carolina varying from 15-38 cm TL (Beane et al. 2010). This subspecies is easily confused with small specimens of the Greater Siren (S. lacertina). The latter is larger and more robust, typically has 37-40 costal grooves between the front limbs and the cloaca, and often has yellowish or pale blotches along the sides.

The hatchlings are the pond type and have conspicuous dorsal fins that extend along the back, short tails, elongated bodies, and partially-developed limbs. The young juveniles in many populations are boldly marked with longitudinal stripes along the body (poorly developed in S. i. intermedia), and yellow to red banding on the head. A broad, dark band with a light streak in the middle occurs on either side of the body. The venter and middorsal region are light colored (Petranka 1998). Small juveniles have a yellow to red, triangular-shaped patch on the snout that often extends laterally to the gills. On some individuals a red or yellow band occurs from each eye towards the base of the gills, and a transverse band may occur across the back of the head. Yellow and red pigmentation may also occur on the feet, near the base of the gills, and on portions of the dorsal fin. The dorsal fins, light body stripes, and red bands and markings on the head progressively disappear with age, and are usually lost within a year.

Vocalizations: Individuals often produce clicking and yelping sounds that may in part play a role in defending burrows (Petranka 1998). Gehlbach and Walker (1970) found that Texas specimens make clicking sounds shortly before or after moving from their burrows towards the water surface to gulp air. When resting in burrows, animals in close proximity may click while simultaneously engaging in head-jerking motions. Resident sirens also tend to click more frequently when intruders are present in an aquarium. Individuals may also emit a yelping sound, particularly when butted or bitten by others.
Online Photos:    Google   iNaturalist
Observation Methods: Individuals are most often collected by dip-netting, electroshocking, or using minnow or crayfish traps.
AmphibiaWeb Account
Distribution in North Carolina
Distribution Comments: Siren intermedia is largely restricted to Coastal Plain wetlands where it occurs from central and southeastern Virginia southward to Florida then westward to south Texas and northeastern Mexico. Populations extend northward through the Mississippi Valley to Indiana, Illinois, and southwestern Michigan. Populations in North Carolina have mostly been found in the southern half of the Coastal Plain, with one isolated population in Bertie County farther north. As of 2022, we have two records from the eastern Piedmont.
Distribution Reference: Beane et al. 2010
County Map: Clicking on a county returns the records for the species in that county.
GBIF Global Distribution
Key Habitat Requirements
Habitat: The Lesser Siren can be found in a variety of permanent or semipermanent habitats, particularly those with dense aquatic vegetation and deep, loose bottom sediments that allow the animals to burrow. Typical habitats include marshes, swamps, abandoned rice fields, farm ponds, ditches, canals, sloughs, and sluggish, vegetation-choked creeks (Beane et al. 2010, Petranka 1998). Seasonal ponds are also used, but typically only those that hold water for most of the year. Snodgrass et al. (1999) surveyed sites in South Carolina for A. means, Siren intermedia, and S. lacertina and found that the likelihood of finding these large aquatic species increased with the seasonal duration of the sites and whether other sites were in close proximity. Sites that held water for less than six months were not occupied by any of these species, and those that were relatively close to adjoining intermittent wetlands were more likely to have populations of Siren intermedia.
Adaptations to Natural Disturbances: Local populations often inhabit semipermanent aquatic habitats that severely contract or dry altogether during major droughts. Individuals respond by burrowing into the bottoms of drying ponds or by enlarging existing crayfish burrows. Lesser sirens have been dug up by excavation crews and by farmers plowing previously flooded fields. They have been found > 0.5 m below the ground surface in J-shaped burrows or crayfish burrows (Petranka 1998). Trapped animals secrete a mucus-like envelope around themselves that progressively thickens to form a parchment-like cocoon that retards dehydration (Gehlbach et al. 1973, Reno et al. 1972). It is not uncommon for sirens to aestivate for several months without food before rains refill the ponds (Cockrum 1941, Gehlbach et al. 1973, Petranka 1998). Aestivating animals have lower heart rates and lower oxygen demands compared to non-aestivating animals. These physiological adaptations lower energy expenditures and increase the time that animals can remain without food (Gehlbach et al. 1973). In laboratory studies, small sirens starve to death within 12-14 weeks after initiating aestivation, whereas large sirens are able to survive at least 16 weeks.
Biotic Relationships: Natural predators are poorly documented but include the Red-bellied Mudsnake (Farancia abacura) and other aquatic snakes (e.g., Ernst and Ernst 2003, Durso et al. 2013), fishes, alligators, and wading birds. The tendency for animals to be nocturnally-active is presumably an antipredator behavior that minimizes predation risk from diurnal predators such as fish and wading birds.
See also Habitat Account for Coastal Plain Still and Sluggish Waters
Life History and Autecology
Breeding and Courtship: The breeding season varies depending on latitude, but is mostly confined to the winter and spring months based on the presence of individuals with bite scars, observations of nests with eggs in early developmental stages, and the presence of gravid and spent females in samples (Petranka 1998). Breeding and egg laying in Louisiana and Florida populations can begin as early as late-December or January (Raymond 1991, Godley 1983), while breeding in the Carolinas occurs in February-April (Collette and Gehlbach 1961, Gibbons and Semlitsch 1991, Sever et al. 1996). The adults tend to become more active during the onset of the breeding season as individuals presumably search for mates (Raymond 1991). Sex ratios of S. intermedia average about 1:1 (Cagle and Smith 1939, Gehlbach and Kennedy 1978).

The females of this species lack spermathecae and the males lack cloacal glands. This led many to surmise that fertilization is external and the males fertilize the eggs as they are laid. External fertilization was finally confirmed by Reinhard et al. (2014) who observed and filmed courtship and parental care in captive animals. They observed a male that actively constructed a nest with aquatic plants within a shelter, then defended the nest and shelter from conspecifics prior to mating. Courtship occurred inside the shelter and initially involved the male and female moving in circles and coiling about each other while undulating the tail tips. The male often pursued the female in close contact to her cloaca, and sometimes rubbed his head against her flank and cloacal region while slightly vibrating his head slowly. During egg laying, the female flipped on her back and attached an egg to the top of the nest. The male followed and pressed his cloaca near the egg where he presumably fertilized the egg before jerking away and returning to his original position. Additional courting and egg laying occurred repeatedly until an estimated clutch of 120-130 eggs were laid. The male became more aggressive with time and would often bite the female along her sides and near her cloacal region. The female eventually left the nest and the male remained to guard the eggs.

Adults taken during the breeding season are often scarred with bite marks which suggests that individuals aggressively defend mates and eggs (Petranka 1998). Spent or ovulated females in Florida often have bite marks on their bodies which may have been inflicted by courting males (Godley 1983). However, bite marks have been found on both sexes in specimens collected from Louisiana during the breeding season (Raymond 1991) and throughout the year in North Carolina (Fauth and Resetarits 1991). These observations suggest that biting may be associated with several phenomenon, including territorial defense by adults outside of the breeding season, courtship, and defense of eggs and nest sites.
Reproductive Mode: Observations in the field indicate that females deposit their eggs singly in large masses or aggregates. The eggs have sticky outer capsules that adhere to each other as well as to vegetation or plant roots. Godley (1983) found two nests in Florida that each had an accompanying female. The nests contained 3-4 layers of eggs that were attached to floating peaty material that was either beneath water hyacinths or a floating clump of grass. Noble and Marshall (1932) found two egg masses in muddy depressions on pond bottoms in Arkansas, while Hubbs (1962) found several nests -- each with an accompanying adult -- in muddy depressions and plant debris in a fish hatchery in Texas. Godley's (1983) discovery of two females in the nests that he discovered is at odds with Reinhard et al.'s (2014) observations in the lab. They found that the female abandoned the nest after ovipositing and the male remained with the eggs during their development. Parental care by the male involved cleaning the nest to remove debris, defending the nest from conspecific intruders, and aerating the eggs through tail fanning and the active movement of his body around the eggs. The embryos hatched after 35 days of development and the male guarded the hatchlings from intruders for another week. It is uncertain if the females observed by Godley (1983) were mothers that were guarding their eggs or merely accidental catches.

Reports for the number of eggs in nests include 206 and 381 eggs at a Florida site (Godley 1983), and 206 and 555 eggs for two Arkansas nests (Noble and Marshall 1932). Clutch size estimates based on dissected gravid females include 224-706 mature ova for 24 southern Illinois specimens (Cagle and Smith 1939), 151, 190, and 226 ova from east-central Texas specimens (Gehlbach and Kennedy 1978), 299 ova for a female from northeastern Arkansas (Noble and Marshall 1932), and a mean of 851 ova (range = 98-1506) for eight other Arkansas specimens (Trauth et al. 1990, Petranka 1998). Two North Carolina specimens that were examined by Collette and Gehlbach (1961) contained 130 and 269 large ova. The freshly laid eggs are dark brown above, 2.5-3.0 mm in diameter, and are surrounded by three jelly envelopes. The diameter of the outer capsule varies from 4.4-7.5 mm (Petranka 1998). The incubation period lasts 1.5-2.5 months based on the first appearance of small larvae in seasonal samples.

The Lesser Siren frequently cannibalizes its eggs. Scroggins and Davis (1956) found 126 siren eggs in 91 specimens that they examined from Texas, while Collette and Gehlbach (1961) found 10 eggs in three specimens from North Carolina. It is uncertain if oophagy reflects nest predation by other sirens or cases of females eating their own eggs (Petranka 1998).
Aquatic Life History: Hatching typically takes place following the spring warm-up. Very little is known about the life history of the hatchlings and the early larval stages. Both the juveniles and adults tend to be secretive during the day and remain either in burrows, in thick vegetation, or beneath cover such as logs, leaf litter, and other bottom debris. They become more active at night and move about in vegetation or on pond bottoms in search of food (Petranka 1998). Individuals hide in individual retreats and rarely aggregate except when shelters are very limiting (Asquith and Altig 1987). Gehlbach and Kennedy (1978) found that most marked individuals in a Texas pond moved less than 6 m from their original point of capture. However, Frese et al. (2003) documented much longer movements at a Missouri site, where the maximum distance between captures was > 10 m for most individuals.

Most juveniles mature during their second year of growth and reproduce for the first time the following winter or spring (Petranka 1998). Davis and Knapp (1953) found that males and females in a Texas pond grew on average about 13 and 10 cm SVL, respectively, during their first year of life, and 7.5 cm and 9 cm during their second year of life. Females matured sexually during their second year when about 15 cm SVL. Cagle and Smith (1939) reported that individuals in southern Illinois matured sexually during their second year of life when 22-25 cm TL. Populations in South Carolina (Gibbons and Semlitsch 1991) and Arkansas (Trauth et al. 1990) also require about 2 years to reach sexual maturity.

The juveniles and adults appear to be gape-limited, generalist predators. Young sirens feed mostly on zooplankton, but also eat larger invertebrates. As they grow, they incorporate larger and more diverse prey into their diets (Petranka 1998). Individuals in a Texas pond primarily ate chironomid larvae, mayflies, water mites, snails, and caddisflies, while those in a swamp in illinois fed on sphaeriid clams, cladocerans, ostracods, copepods, isopods, amphipods, odonates, beetles, dipterans, and other insects. The prey of three North Carolina specimens included odonates, isopods, and conspecific eggs (Collette and Gehlbach 1961). Individuals from Texas consumed a similarly wide variety of prey, including both aquatic and terrestrial prey that may have washed into ponds during heavy rains (Scroggins and Davis 1956).

In addition to animal remains, the gut contents often include large amounts of filamentous algae, pieces of vascular plants, and mud and bottom debris (Bennett and Taylor 1968, Davis and Knapp 1953, Noble and Marshall 1932, Scroggin and Davis 1956). Bottom debris in the diet may reflect a common feeding behavior that involves gulping in bottom debris and filtering out small clams and other food as water is passed through the branchial openings (Petranka 1998). The presence of filamentous algae and other green plant material in the guts of sirens have caused some to consider whether S. intermedia derives energy from plant material. Recent studies of both the Lesser Siren and Greater Siren suggest this may be the case. Both species have a complex chewing mechanism that may allow individuals to crush and process plant material to some extent before swallowing. They are known to intentionally eat algae, have a complex and intensely folded gastrointestinal tract that could support plant-digesting microbes, and show evidence of fermentation occurring in the gut (Hill et al. 2015, Pryor et al. 2006, Schwartz et al. 2021).


General Ecology
Population Ecology: The densities and biomasses that this species reaches in optimal habitats is remarkably high. Gehlbach and Kennedy (1978) estimated the density and biomass of sirens in optimal habitats in a Texas pond as 1.1 animals /m2 and 46.2 g/m2, while Frese et al. (2003) provided estimates of 1.35-2.17 sirens/m2 and 44.9-72.2 g/m2 in a Missouri wetland. Density-dependent interactions may ultimately set an upper limit on local population size given that males are aggressive towards other males and probably defend territories (Reinhard et al. 2014).
Community Ecology: Fauth and Resetarits (1991) used artificial pond communities to examine interactions between S. i. intermedia, the Eastern Newt (Notophthalmus viridescens), and five species of anuran tadpoles that coexist in ponds in North Carolina. Sirens were capable of reducing the growth and survival of newts when at high densities, but this enhanced newt reproductive success by releasing newt larvae from intraspecific competition and cannibalism. The presence of newts has no effect on siren survival or growth rate, and neither the direct or indirect effects of sirens altered the role of the Eastern Newt as a keystone predator in these experimental communities. Fauth (1999) also examined interactions between S. i. intermedia and gilled adults of the Mole Salamander (A. talpoideum) and provided evidence that S. i. intermedia competes with and is an intraguild predator of A. talpoideum.
Adverse Environmental Impacts
Habitat Fragmentation: Severe, prolonged droughts likely result in the extinction of some local populations (Snodgrass et al. 1999). Recolonization of sites following a local extinction event likely occurs during major floods when these sites are connected temporarily via aquatic corridors to adjoining sites with sirens. Lesser Sirens are mostly aquatic, but they have been found on land substantial distances from water and may be capable of limited overland movement (Leja 2021). Although they largely survive droughts by aestivating underground, it is possible that pond drying could trigger some individuals to emigrate short distances to adjoining water bodies during rain events. Roadways likely act as major barriers to both aquatic and terrestrial dispersal between wetlands and could act to fragment landscapes.
Status in North Carolina
NHP State Rank: S4
Global Rank: G5

Photo Gallery for Siren intermedia - Lesser Siren

4 photos are shown.

Recorded by: Rob Van Epps
Moore Co.		Recorded by: Jeff Beane
Scotland Co.
Recorded by: Jeff Beane
Scotland Co.		Recorded by: Jeff Beane
Scotland Co.