Common Siren

A large, eel-like, aquatic salamander. Greater sirens, like other members of the family Sirenidae, lack hindlimbs and eyelids, have horny beaks on the upper and lower jaws, and are gilled throughout life (Martof 1974). Greater sirens have four toes on the front limbs and three gill slits (Martof 1973; 1974; Petranka 1998). Adults range from 50 - 98 cm total length but most are less than 70 cm (Petranka 1998). The tail is 26 - 40% of the total length (Martof 74). There are ventral and dorsal fins on the tail (Martof 1973). Modal number of costal grooves is 37-38 (Martof 1973; Petranka 1998). Adult males have enlarged jaw (masseter) muscles which make the head appear larger than in females (Petranka 1998). Hatchlings are 16 cm total length (13 cm snout to vent length), and possess a relatively shorter tail than adults and a tail fin which extends from the base of the head to the tip of the tail (Martof 1973).Adult coloration varies from olive green to light gray above and sometimes there are dark spots on the head, back and sides. The sides are lighter colored than the dorsum and usually have flecks of pale green. The venter is bluish grey and often has pale green flecks. Description from Petranka (1998). Juveniles have light, often yellow, body stripes that fade with age (Martof 1973; Petranka 1998).No subspecies are currently recognized, but geographic variation is poorly understood (Petranka 1998). The recent report (Flores-Villela and Brandon 1992) that greater sirens occur in Texas and Mexico (previously specimens were thought to be S. intermedia) is a large extension to the known range and suggests that detailed surveys across the distribution of greater sirens may uncover interesting patterns.

Occurs in coastal plain habitats from the vicinity of Washington, D. C., to southern Florida and westward to southwestern Alabama (Petranka1998). Greater sirens have also been documented from localities in southern Texas and northeastern Mexico (Tamaulipas) (Flores-Villela and Brandon 1992).Greater sirens inhabit a variety of permanent and semi-permanent aquatic habitats, including ditches canals, marshes, rice fields, lakes, and slow-moving streams and rivers (Petranka 1998). Sites are often muddy or heavily vegetated. Young are often found among water hyacinth roots (Martof 1973)

In northern and western portions of the range, greater sirens are patchily distributed. More understanding of these peripheral populations is needed (Petranka 1998). Diminshing availability of wetland habitats is a threat to greater siren populations.

Courship and mating have not been observed. Fertilization is presumed to be external (Martof 1974; Sever et al. 1996). Few nests have been found in nature. Females apparently lay eggs in late winter to early spring (February to March) (Petranka 1998). Eggs are laid in small groups of less than 10 eggs, although a single female may lay more than 100 eggs total (Petranka 1998 and references therein).Greater sirens eat a range of prey items, including a high proportion of molluscs (snails and freshwater clams). Animals are active primarily at night and retreat to burrows during the day. When temporary pools of water dry up, sirens will aestivate underground and can easily survive for months. Greater sirens vocalize using clicks and yelps, as do lesser sirens. These sounds are produced when animals are disturbed and also may serve for intraspecific communication. Greater sirens are locally abundant in Florida, Georgia, and eastern South Carolina. See Petranka (1998) and references therein.Despite their large size and abundance in some regions, relatively little is known about the biology and ecology of greater sirens.

Maximum longevity: 25 years (captivity)

Little is known about the expected lifespan of greater sirens in the wild or captivity. However, a single greater siren residing in the Cincinnati zoo has been reported to be at least 25 years of age.

Range lifespan
Status: captivity: 25 (high) years.

Average lifespan
Status: captivity: 25.0 years.

Average lifespan
Sex: female
Status: captivity: 14.8 years.

Greater sirens have been found in the digestive tracts of American alligators and red-bellied mud snakes. Otherwise, little is known about their predators. To avoid predation, greater sirens employ several techniques. They can produce an array of sounds that can intimidate predators. These include yelps (similar to calls made by green tree frogs), hissing, croaking and a sound similar to that of a young duck. In addition, greater sirens may use their muscular tails to make a hasty getaway. As a last resort, a greater siren can deliver a painful bite to ward off predators.

Known Predators:

• red-bellied mud snakes (Farancia abacura)
• American alligators (Alligator mississippiensis)

Anti-predator Adaptations: cryptic

Greater sirens have a similar overall body shape to other salamanders, but have reduced forelimbs (containing four toes each) and no hind limbs giving, them rather eel-like appearance. Their body is round in cross section and encompasses about two thirds of their total length, with the rest being composed of a long, vertically flattened tail. The head is rounded into a square jaw with one small eye on each side. They possess external gills with three gill appendages a few centimeters behind their eyes, but before their legs. These appendages are crowded in the front of the body as opposed to being spread-out. Their skin is an olive or grayish brown color with black speckles and yellow dashes along its length (particularly on the dorsum). The underbelly tends to be lighter in color than the skin on the sides and back. Greater sirens can reach a length of 97 cm, but average around 62 to 77 cm.

Greater sirens can be distinguished from lesser sirens (Siren intermedia) by counting the number of costal grooves (lateral indentations that run down the length of a salamander's body) present. Greater sirens have 36 to 40 costal grooves as opposed to the 31 to 35 costal grooves found on lesser sirens. Additionally, lesser sirens are uniformly dark, more slender, and have sharper tails. Newly hatched greater sirens are striped and have a yellow or red triangular marking on their snout, while newly hatched lesser sirens lack stripes and snout markings.

Range length: 49 to 97 cm.

Average length: 62 - 77 cm.

Sexual Dimorphism: sexes alike

Other Physical Features: ectothermic ; bilateral symmetry

Unlike many salamanders, greater sirens lack a terrestrial life stage and are found exclusively in aquatic environments for their entire lifespan. They prefer the shelter of heavily vegetated swamps, ponds, and ditches, but are also found in streams and large lakes. They migrate to shallow water in order to lay their eggs. Hatchlings live among thick vegetation (such as the roots of water hyacinth) and progressively move to deeper water as they mature. Adults spend the majority of their time near the bottoms of pools, entwined in plant roots and branches, or under sunken logs. When bodies of water dry out, greater sirens burrow into the muddy lake or stream bed and enter a state of aestivation to avoid dessication.

Habitat Regions: temperate ; freshwater

Aquatic Biomes: lakes and ponds; rivers and streams; coastal

Wetlands: swamp

Greater sirens are found in the southern and eastern United States, along the Atlantic and Gulf coastal plains. They can be found as far north as eastern Virginia and south through the southern tip of Florida, and as far west as southwestern Alabama. There are reports of a disjoint population occupying the Rio Grande valley of southern Texas and northern Mexico. However, further investigation is required to assess the relationship of the two populations.

Biogeographic Regions: nearctic (Native )

Greater sirens are active at night and are primarily carnivorous. However, algae has been found in the digestive tract of some individuals, leading researchers to believe that they may be omnivorous. Greater sirens will prey on insects, crustaceans, gastropods, bivalves, spiders, mollusks, crayfish, and small fish.

Animal Foods: fish; insects; terrestrial non-insect arthropods; mollusks

Plant Foods: algae

Primary Diet: carnivore (Insectivore , Eats non-insect arthropods, Molluscivore ); herbivore (Algivore)

Greater sirens act as mid-level predators, feeding on insects and other invertebrate species. Greater sirens are also hosts to platyhelminth parasites, including flatworms (Ophiotaenia sireni and Progorgodera foliata) and trematodes (Allassostomoides louisianaensis).

Commensal/Parasitic Species:

• trematodes (Allassostomoides louisianaensis)
• flatworms (Ophiotaenia sireni)
• flatworms (Progorgodera foliata)

Greater sirens benefit humans by keeping aquatic invertebrate and insect populations in check.

Positive Impacts: controls pest population

There are no known adverse effects of greater sirens on humans.

Greater sirens retain larval features throughout life. Their gills remain external throughout their life and they never develop hind limbs. Hatchlings are approximately 11 mm in length and are born with distinct stripes, which gradually fade and are completely lost within the first year of life. Newly hatched individuals will also have a red or yellow triangular marking on their snout. Juveniles tend to be brighter in color and have a more mottled appearance when compared to adult specimens.

Development - Life Cycle: neotenic/paedomorphic; metamorphosis

Greater sirens are considered common throughout the central regions of their geographic range. However, their status throughout the peripheral regions of the range varies between abundant and rare. In Maryland, they are considered endangered. Greater siren populations are difficult to monitor, due to their permanently aquatic lifestyle. Encroachment on habitats by agricultural and urban development, including runoff of harmful pesticides, is the major potential threat to greater siren populations.

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

IUCN Red List of Threatened Species: least concern

Because greater sirens are solitary and seldom interact, little information is available regarding modes of intraspecific communication. They are known to produce hissing sounds when threatened by predators, however.

Because the eyes of greater sirens are rather small and they often inhabit areas of high water turbidity or otherwise low visibility, vision is likely to be a secondary sensory modality by which this species perceives its environment. They use an auxilliary olfactory organ (the vomeronasal or Jacobson's organ) to detect prey in these situations. They are also likely to use their lateral line (which most larval amphibians possess and which greater sirens maintain throughout their adult lives) to sense vibrations in their environment. It is thought that they may also be able to sense disturbances in electrical fields using dense arrays of neuromasts that are found on the head.

Communication Channels: acoustic

Perception Channels: visual ; tactile ; acoustic ; vibrations ; chemical ; electric

Specifics of greater siren mating systems are unknown.

Greater sirens reach reproductive maturity around the age of two to three years. Mating behavior has yet to be observed and reported for this species. However, as in other amphibians, fertilization is assumed to be external. Greater sirens breed once yearly between February and March, although this depends on environmental conditions. Females lay a large clutch of about 500 eggs, which look like small grapes and adhere to each other. The eggs gestate for about two months and hatch in the months of April or May.

Breeding interval: Greater sirens breed once yearly.

Breeding season: Breeding occurs from February to March.

Average number of offspring: 500.

Average time to hatching: 2 months.

Average age at sexual or reproductive maturity (female): 2 years.

Average age at sexual or reproductive maturity (male): 2 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (External ); oviparous

Female greater sirens will guard their eggs in the shallows until they hatch and then return to deeper water. No further parental protection occurs.

Parental Investment: pre-fertilization (Provisioning); pre-hatching/birth (Protecting: Female)

The greater siren (Siren lacertina) is an eel-like amphibian and one of the three members of the genus Siren. The largest of the sirens and one of the largest amphibians in North America, the greater siren resides in the coastal plains of the southeastern United States.