Lesser Siren Siren intermedia

Description: Adult Morphology: A very distinctive eel-like, aquatic salamander with a long slender body and a narrow head with obvious external gills. Sirens completely lack rear legs, and the front legs have four digits. Coloration is variable, but dorsal color is grayish to brown with some dark spots present. Large yellow stripes are present on the sides of the head.

Size: Adult sirens range from around 1 ft to slightly over 2 ft in length, although most sirens captured in Indiana have been under 20 in (~180-400 mm).

Larvae: Superficially, siren larvae differ very little in appearance from the adults with the exception of some reddish or orange coloration around the head, and some dorsal striping that disappears at a very young age.

Eggs: Little is known about siren breeding, but clumps of eggs have been found at the bottom of ponds in Arkansas and clutch size has been estimated to be 200-700 eggs. They presumably attach eggs to vegetation or other debris.

Similar Species: The long, slender body and lack of rear legs easily distinguish this species from all other aquatic salamanders and salamander larvae found in the state.

Distribution: Lesser sirens are found throughout the coastal plain of the southeastern United States from North Carolina to Texas and Oklahoma, and northward along the Mississippi and Ohio River floodplains into Illinois and Indiana, with populations extending into southern Michigan (though populations in Michigan may be extirpated).

Sirens are known from the Ohio, Wabash, and Kankakee river drainages of western Indiana, and from a single locality in the Northern Lakes region (Great Lakes drainage) of northeastern Indiana. Historically, sirens may have occurred in wetlands throughout western and north-central Indiana, but recent records are confined to the lowlands of southwestern Indiana and the swamps of northwestern Indiana, with only a few scattered records in between. Their known distribution is patchy throughout the west-central part of the state and may be largely associated with floodplain habitat along the Wabash River.

Activity: Sirens are active year round and can be captured even when wetlands are iced over. They are generally most active during the winter and spring in the south. Sirens will aestivate underground during hot, dry weather.

Breeding Season: Breeding apparently takes place during winter and early spring and eggs are likely deposited in the spring and early summer. Very little is known about breeding in this species, and it has never been observed.

Taxonomy: Sirens in Indiana belong to the western subspecies (Siren intermedia nettingi). The family Sirenidae is a very primitive group of salamanders that is considered to be the sister group to all other living salamanders. Only two genera are extant within this family, with only a few species in each genus—all of which occur in the southeastern United States.

Ecology: Habitat: Sirens are primarily a lowland species commonly occurring in floodplains and low-lying wetlands. Though they can be abundant in natural wetlands and sloughs, sirens will also utilize artificial habitat such as drainage ditches, constructed ponds, and flooded farmfields. This species has the ability to breath using either lungs or gills and can burrow into the mud and cocoon themselves in mucous to aestivate during dry periods. This behavior allows sirens to colonize ephemeral habitats that connect to more permanent bodies of water during flood periods. Isolated ephemeral habitats may be avoided due to the stress that prolonged aestivation has on the animals. Unlike other large aquatic salamanders, sirens may reach very high population densities when conditions are optimal; indeed, hundreds of adults have been captured in relatively small wetlands.

Diet: Sirens feed mainly on small insects and crustaceans such as isopods, amphipods, copepods, and ostracods. Due to their unique head morphology and small gape size they likely use indiscriminate suction feeding, a theory which is reinforced by the regularity with which plant matter is found in their gut.

Reproduction and Life History: Breeding has not been observed in this species, but fertilization is presumed to be external. Eggs are deposited in clumps of vegetation in still water habitats such as swamps, sloughs, and flooded lowlands.

Conservation: Though sirens are sometimes found in abundance at sites in Indiana, their distribution remains poorly understood, especially in west-central and north-central Indiana. They are often found in agricultural drainage ditches, sometimes in large numbers and it is likely they adapt well to such modifications. A recent study in southeastern Missouri found that sirens were more abundant in some artificial wetland impoundments (moist soil units) than in neighboring forested wetlands. This trend seems to reflect a greater availability of food in the moist soil units.

Literature

Altig, R. 1967. Food of Siren intermedia nettingi in a Spring-fed Swamp in Southern Illinois. American Midland Naturalist 7:239-241.

Brodman, R. 2003. Amphibians and Reptiles from Twenty-three Counties of Indiana. Proceedings of the Indiana Academy of Science 112.1:43-54.

Conant, R. and J. T . Collins. 1998. Reptiles and Amphibians of Eastern and Central North America. Third Edition, Expanded. Houghton Mifflin, New York, New York.

Frese, P. W., A. Mathis, and R. Wilkinson. 2003. Population Characteristics, Growth, and Spatial Activity of Siren intermedia in an Intensively Managed Wetland. The Southwestern Naturalist 48:534-542.

Gehlbach, F. R. and S. E. Kennedy. 1978. Population Ecology of a Highly Productive Aquatic Salamander (Siren intermedia). Southwestern Naturalist 23:423-430.

Gehlbach, F. R., R. Gordon, and J. B. Jordan. 1973. Aestivation of the Salamander, Siren intermedia. American Midland Naturalist 89:455-463.

Hoffman, A. S. 2012. Occupancy and Detection Rates of Salamanders in Association with Altered Water Regimes at Mingo National Wildlife Refuge in Southeastern Missouri. Missouri State University, Thesis.

Minton, S. A. Jr. 2001. Amphibians and Reptiles of Indiana. Indiana Academy of Science, Indianapolis, IN.

Petranka, J. W. 1998. Salamanders of the United States and Canada. Smithsonian Institute Press, Washington D.C.

Snodgrass, J. W., J. W. Ackerman, A. L. Bryan Jr., and J. Burger. 1999. Influence of Hydroperiod, Isolation, and Heterospecifics on the Distribution of Aquatic Salamanders (Siren and Amphiuma) among Depression Wetlands. Copeia 1:107-113.

Sullivan, A. M. 1999. Reproduction, Body Condition and Dietary Variation of the Lesser Siren (Siren intermedia). Missouri State University. Thesis.

Distribution Map
Distribution map of Lesser Siren (Siren intermedia)
Photographs