SPOTTED SALAMANDER
Ambystoma maculatum
 
INTRODUCTION

The spotted salamander is Rhode Island's most widespread mole salamander. The mole salamanders (Ambystomids) are a secretive group of organisms that are primarily active at night, rarely seen except in migration during their brief breeding season, and are adapted to cool, moist conditions. When they are encountered, this species is easily identified by its black body with bright yellow spots.

The two Ambystomids that have been documented in Rhode Island are the relative common spotted salamander and the much rarer marbled salamander (A. opacum). A congener, blue-spotted salamander (A. laterale), was incorrectly reported by Degraaf and Yamasaki (2001) as occurring the state because it has never been collected in Rhode Island (C. Raithel, pers. comm.). Spotted salamanders are relatively abundant in Rhode Island and have been detected in most towns in the state. They are most evident during mass movements on rainy nights during March and April while immigrating to or emigrating from breeding ponds. During spring migration events, dozens can be seen crossing roads throughout the state. This, in turn, results in large numbers of spotted salamander killed each year by vehicles. In fact, road mortality is one of the primary threats to the long-term stability of spotted salamanders in the state.

Spotted salamanders actually spend little time at breeding ponds. During most of their annual cycle, they reside in upland forests away from breeding ponds. Adults typically reside up to 200 m from breeding ponds (Windmiller 1996; Semlitsch 1998), although adults in certain habitat have been documented moving much greater distances of >400 m (B. Windmiller, pers. comm.). Spotted salamanders typically live in burrows, very often using shrew (Blarina brevicauda) burrows (Semlitsch 1998), in areas with well-drained soils (Windmiller 1996). They appear to be habitat generalists, as the areas we have detected them in Rhode Island include deciduous, coniferous and mixed forest types (S. Egan, unpubl. data).

 
IDENTIFICATION
  • The only large salamander in Rhode Island with bright yellow spots.
  • Spotted salamanders are a relatively large amphibian, with adult total length ranging from 12.5 - 23.0 cm (P. Paton, unpubl. data)
  • Dorsal color is black, slate-gray, gray-brown, or blue-black (Conant and Collins 1991; Smith 1999), with bright yellow rounded spots on the back and tail.
  • Ventral color is dark grayish to black.
  • Adults and juveniles have 30-50 round, yellow spots (Conant and Collins 1991, Bishop 1941) irregularly arranged in two rows along each side of the mid-dorsal line (Smith 1999).
  • In some regions of North America, individuals have orange head spots (Minton 1972; Downs 1989), but this color variation has not been observed in Rhode Island (P. Paton, pers. obs.).
  • Unspotted individuals are rare but most likely occur through their range (Conant and Collins 1991). We have never documented any unspotted adults in Rhode Island, although we have seen some with faint yellow spotting (P. Paton, pers. obs.).
  • Metamorphs as they first emerge from breeding ponds are often solid black with no yellow spots, but in <7 days out of the water their spot pattern becomes quite evident (P. Paton, pers. obs.)
  • The usual number of costal grooves is 12, sometimes 11 or 13 costal (Bishop 1943).

Sexual Dimorphism

  • During the breeding season (March in Rhode Island)

    • the female venter is lighter in color than the male, usually a slate-gray
    • yellow spots on the male become brighter (Smith 1999).
    • males have a swollen vent, that appears relatively square with small granules on the distal end.
  • Some females are considerably larger than males (Klemens 1993; Paton-see below).
  • A note of caution, the vent of males emigrating from breeding ponds often lacks this distinctive appearance, therefore determining gender in much more difficult in April. Therefore, non-breeding males are best identified by the presence of a series of parallel ridges on the inside of the cloaca (Petranka 1998a).

Female venter (top), male venter


 
SIZE
AGE / SEX
SVL (SNOUT VENT LENGTH) (cm)
SAMPLE SIZE

AVERAGE

RANGE

Std. deviation

ADULT FEMALE

9.0

7.2-10.5

0.8

85

ADULT MALE

8.0

6.1- 9.7

0.8

76

JUVENILE

5.1

3.1- 7.5

1.4

11

METAMORPH

3.3

2.2- 5.0

0.5

339


AGE / SEX TL (TOTAL LENGTH)
SAMPLE SIZE

AVERAGE

RANGE

Std. Deviation

ADULT FEMALE

18.1

15.2- 23.0

1.5

85

ADULT MALE

16.6

14.0- 19.2

1.4

76

JUVENILE

10.3

5.5- 14.5

10.3

11

METAMORPH

6.4

3.6- 9.5

1.2

339



AGE/ SEX
MASS (g)
SAMPLE SIZE

AVERAGE

RANGE

Std Deviation

ADULT FEMALE

22.7

11.4- 35.9

5.1

85

ADULT MALE

15.6

10.1- 26.0

3.7

76

JUVENILE

5.2

0.8- 9.3

3.0

11

METAMORPH

1.32

0.3- 3.7

0.6

339









 
RELATIVE ABUNDANCE
Rhode Island
Spotted salamanders are widespread throughout Rhode Island. They occur across the urbanization gradient in the state, ranging from rural areas in western Exeter to urban parks in Lincoln. During surveys we conducted at breeding ponds west of Narragansett Bay, spotted salamanders were detected breeding in 87 of 119 ponds (73%) (Paton and Egan 2000). Our fieldwork suggests there are more suitable breeding sites in rural and suburban areas than in urban areas.
Regional
Common throughout mainland New England from sea-level to high elevations (Klemens 1993). Burne (2000) documented them at ~71% of 78 randomly selected ponds in Concord, Massachusetts, which was remarkably similar to the relative abundance we documented for the species in Rhode Island. It appears they are widespread throughout the region. Some populations appear to be declining, possibly due to acid precipitation and over-collection (Degraaf and Rudis 1983).
 
DISTRIBUTION
Rhode Island
Spotted salamanders are found throughout mainland Rhode Island and on two of the larger Narragansett Bay Islands (Klemens 1993).
Regional
Widespread throughout mainland New England (Klemens 1993). Reportedly on Martha's Vineyard, but not Nantucket (Degraaf and Yamasaki 2001; Klemens 1993) or Block Island (C. Raithel pers. comm.).
General
Spotted salamanders are found throughout eastern North America, ranging as far north as southern Quebec and the Canadian maritime provinces, as far south as northern Florida (with scattered area where they absent [e.g., parts of Virginia and New Jersey]), and as far west as northeastern Wisconsin, and eastern Texas (Klemens 1993; Petranka 1998a).
 
HABITAT NON BREEDING

Aside from the brief period spent at breeding sites, spotted salamanders are entirely terrestrial. They are most abundant in mature deciduous or mixed, mesic woods where slow moving streams, ponds, or vernal pools offer optimal breeding habitat (Smith 1999; Petranka 1998a; Bishop 1943). Windmiller (1996) further described the prime forested habitat to consist of well-drained soils and ample woody debris for cover.

Spotted salamander are nocturnal and fossorial. Therefore, they are seldom encountered except during the breeding season (Ptingsten and Downs 1989; Paton and Crouch In press). This is particularly true during the summer, as during 3 years of running drift fence arrays throughout the year we never captured any adults from May through August (Paton and Crouch In press). They spend most days hunkered down under leaves, logs and other debris, or in underground burrows (Smith 1999). A study conducted by Semlitsch (1983) found that Ambystoma maculatum utilize invertebrate and mammal burrows (usually short-tailed shrew [Blarina brevicauda]), cracks, and crevices rather than digging their own shelter. During the coldest months of winter, spotted salamanders hibernate in these refuges.

 
HABITAT BREEDING

Fishless temporary ponds in mature deciduous forests are preferred breeding sites for Ambystoma maculatum throughout their range (Petranka 1998a); however, Klemens (1993) in Connecticut observed breeding activity in a wide array of wetlands including floodplain swamps, marshes, bogs, margins of lakes and reservoirs, beaver impoundments, pasture ponds, ornamental ponds, non-chlorinated swimming pools, gravel and sand pit ponds, springs, ruts in dirt roads, and backwaters of streams and small rivers. In Rhode Island, we documented them breeding in a similar variety of aquatic habitats (S. Egan, unpubl. data).

According to Gates and Thompson (1981), who studied 115 ponds in Western Maryland, spotted salamanders favor shallow ponds with abundant leaf litter, and other debris on the pond bottom rather than deep(er) ponds with exposed substrate. They reported that spotted salamanders tend to utilized ponds with moderate (< 50% cover) to dense ( > 50% cover) vegetation on the shoreline (Gates and Thompson 1981).

 
HYDROLOGY
 
MOVEMENT CHRONOLOGY
Adult immigration
Arrival time of adults to breeding sites appears to be influenced strongly by annual variation in environmental conditions (Savage 1935, Packer 1960, Frazer 1966, Hurbert 1969, Gittin 1983, Semlitsch 1983, Semlitsch et. al. 1993). The breeding season may last from 3 days to over 2 months with major breeding sessions occurring on nights during or immediately following rain, snowmelt, or high humidity (Peckham and Dineen 1954; Mount 1975; Harris 1980; Sexton et al. 1986; Petranka 1998a). In Rhode Island, immigration to breeding ponds typically begins around 1 March (Paton and Crouch In press), as long as climatic conditions are suitable. If extensive snow covers the ground, or drought conditions exist, spotted salamanders will not migrate to breeding ponds (P. Paton, unpubl. data). Most adults are in breeding ponds by mid-March in Rhode Island, although some adults may be detecting entering ponds as late as 10 April (Paton and Crouch In press). Male salamanders tend to arrive at breeding ponds first, followed by the females a few days later. Upon the female's arrival, the elaborate courtship display or nuptial dance begins (Petranka 1998a).

Metamorph emigration
Metamorphs leave the ponds within a few weeks after transforming and disperse into the surrounding forest during rainy weather (Petranka 1998a). In Rhode Island, we documented a relatively protracted dispersal period for metamorph spotted salamanders (Paton and Crouch In press). Metamorphs in Rhode Island initiate emigration around 20 July, with the majority of metamorphs departed by mid-August. However, stragglers can continue to emerge from ponds into early October. We have seen ponds dry up completely and metamorphs emigrate from the waterless pond basin 2 weeks later (P. Paton, unpubl. data).

Shoop (1974), working in western Rhode Island, documented productivity estimates of 15.1 (± 6.1 [SE]) metamorphs successfully emigrating for each breeding female entering the pond.

 

 
REPRODUCTION

Adults are highly site faithful to their breeding pond (Ptingsten and Downs 1989). McGregor and Teska (1989) found that olfaction plays a major role in aiding adults in orienting towards their home pond. In fact, Shoop (1965) found migrating spotted salamanders tend to enter and leave breeding ponds near the same point each year. When the females enter the pond, the nuptial dance begins near the water's edge. Typically, many individuals congregate and swim about vigorously nudging and rubbing each other repeatedly. Often, males outnumber females by more than a 2 to 1 margin, so intrasexual competition is high. While in pairs, a male circles around a female, swinging his head back and forth over her dorsum and lifting his head under her chin (Petranka 1998). Later in the dance, males alternate between nudging and depositing spermatophores on the pond's bottom- usually a short distance away from the activity center (Ptingsten and Downs 1989). Most spermatospores are deposited in the same area, with the competitive males frequently stacking one spermatophore on top of another, sometimes as many as six high (each males produces an average of 40 spermatophores) (Ptingsten and Downs 1989).

During courtship, a female locates and positions herself over the spermatophores, then grasps them within her cloaca, as fertilization is internal. In an experiment conducted by Arnold (1976), females were able to locate about 40% of the spermatophores in an artificial setting (Ptingsten and Downs 1989). The eggs are held within her body for several days before being laid (Smith 1999).

 
EGG MASS
Within a few days after mating, eggs are deposited in firm spherical, elongate, or kidney-shaped masses and in most cases attached to submerged objects (alive or dead herbaceous and woody vegetation) (Kenney and Burne 2000; Bishop 1943). It is common to find egg masses deposited directly on the pond floor (Sexton et al. 1986; Petranka 1998); we see this very often in Rhode Island (S. Egan, unpubl. data). The compact mass initially measures 6.5-9.0 cm in diameter (Bishop 1943), but quickly expands as it absorbs water; individual eggs are 2.5 -3.0 mm in diameter. There is a smooth outer gelatinous membrane surrounding the egg aggregation, which gives clear egg masses (see color types below) a halo appearance surrounding the dark embryos. In contrast, wood frogs (Rana sylvatica) egg masses lack the smooth outer membrane and therefore are bumpy.
Spotted salamander egg mass

The average number of embryos reported per egg mass is approximately 125, but varies from a less than 20 to 250 (Degraaf and Yamasaki 2001; Smith 1999; Pfingsten and Downs 1989). The entire aggregation may be deposited as a single mass or up to half a dozen small masses (Pfingsten and Downs 1989). At a site in Wellesley, Massachusetts, Shoop (1974) reported an average of 224 ovarian eggs per female (n=22). In another study, Woodward (1982) found that females breeding in permanent ponds had larger clutch sizes on average than those using temporary ponds; 182 eggs per clutch (n=16) and 233 eggs per clutch (n=24) respectively. Woodward (1982) also found that females using the temporary pond produced significantly larger individual eggs than those using the permanent pond. His study reported that although larger eggs did not hatch earlier than smaller ones, the hatchlings were larger, reached the feeding stage significantly sooner, and thus were able to undergo metamorphosis and leave the breeding site earlier.

There are three color types of spotted salamander egg masses- milky-white, clear, and intermediate; color is dependent on the presence of proteins in the outer jelly layers (Ruth et al. 1993). Milky-white and clear forms appear to be equally distributed and sympatric, whereas the intermediate color variation may be rare or absent in local populations (Ruth et al. 1993). In a 2000 study in Rhode Island, we found egg masses in 87 ponds- none were of the intermediate stage (S. Egan, unpubl. data).

The incubation period reported for spotted salamander varies from 31 to 54 days (Bishop 1947) to 42 to 56 days (Kenney and Burne 2000) to as long as 60 days in a cold spring fed pond in Rhode Island (Whitford and Vinegar 1966) depending on the temperature of the water. Petranka (1998a) reported considerable intra- and interannual variation in the embryonic period within the same population.
 
 
LARVAE

The length of the larval period varies greatly and seems to be dependent on water conditions including hydroperiod and pond temperature, as well as food supply (Shoop 1974). At hatching, the average larva measures 12-13 mm (0.5 inches), and has feathery gills, fore limb buds, and a pair of balancers (Bishop 1943). The balancers disappear after a few days and the gills will disappear as the larva undergoes metamorphosis (Kenney and Burne 2000). Larvae grow rapidly and most metamorphose within 2-4 months (Petranka 1998); however, larval periods can be shorter or longer depending on environmental conditions. When temporary ponds begin to dry up, larval have the ability to transform earlier. And, by the same token, at ponds with longer hydroperiods, larval tend to metamorphose at later date and larger size. Wilbur and Collins (1973) found that, even in a single pond, development rates varied - with individuals transforming from 57 to 144 days. In another study, Shoop (1974) documented a difference of 60 sixty days between the emergence of the first and last metamorph. Furthermore, some larvae overwinter, as Whitford and Vinegar (1966) documented overwintering larvae in a cold spring-fed pool near Kingston, Rhode Island. In addition, S. Egan (unpubl. data) documented an overwintering A. maculatum larvae in Exeter, Rhode during the 2000 field season.

On average, larvae attain a length of 6.5 cm (2.5 in) (Bishop 1943) at which time larvae transform into miniature adults and exit breeding ponds (Smith 1999). Adult spot patterns are generally acquired within a week after metamorphosis (Bishop 1943), a phenomenon that we have observed in Rhode Island (P. Paton, pers. obs.).

 
METAMORPHS
 
spotted salamander metamorph
 
JUVENILES

During three-years of monitoring the movement phenology of pond-breeding amphibians in southern Rhode Island, we rarely captured juvenile A. maculatum (Paton and Crouch In press). As Petranka (1998a) noted, metamorphs that successfully emigrate from breeding ponds must spend most of their annual cycle underground, as juveniles, in burrows waiting until they are old enough to reach sexually maturity. They are rarely captured above ground, either near breeding ponds or even in upland forest away from breeding ponds (P. Paton, unpubl. data).

Sexual maturity: Wilbur (1977) reported that in Michigan, males mature after 2-3 years and females reach maturity after 3-5 years (Petranka 1998a). Wacasey (1961) found males mature during the second year, and females a year later (Degraaf and Yamasaki 2001).

 
FOOD
Adults
Spotted salamanders are generalized carnivores that forage in rotting logs and debris for a variety of invertebrates (Ptingsten and Downs 1989) including earthworms, snails, slugs, insects and larvae, spiders, and beetles (Degraaf and Yamasaki 2001). Cannibalism also occurs (Smith 1999). Adults do not feed on during spring migration or at the breeding sites (Bishop 1941; Petranka 1998a).
Larvae
Small larvae feed predominantly on cladocerans and copepods (Freda 1983; Petranka 1998a; Ptingsten and Downs 1989) Larger individuals feed on snails, clams, oligochaete worms, small aquatic insects and their larvae, other invertebrates (Kenney and Burne 2000; Ptingsten and Downs 1989; Wilbur 1972). and red-spotted newt larvae (Notophthalmus viridescens) (Petranka 1998a). Zooplankton is the dietary staple of larvae of all size classes (Petranka 1998a). Cannibalism by larvae occurs under crowded conditions (Degraaf and Yamasaki 2001).
 
PREDATION
Adults
The noxious skin secretion and bright spotting protects adults from some predators but not all (Petranka 1998a). Klemens (1993) dissected spotted salamanders from the stomachs of a garter snake (Thamnophis siralis) and Babbitt (1932) reported consumption by a hognose snake (Heterodon platirhinos). Huheey and Stupka (1967) found remains of spotted salamanders that were attacked by raccoons in eastern Tennessee (Petranka 1998a).
Larvae
Larvae are eaten by predatory insects- predaceous diving beetles, their larvae, water boatman, dragonfly nymphs, water scorpions and giant water bugs- other Ambystoma larvae, as well as turtles (Kenney and Burne 2000). Stangel (1983) witnessed least sandpipers (Calidris pusilla) feeding on larvae in a Massachusetts pond (Petranka 1998a). Petranka et al. (1998) found that wood frog tadpoles can be a major predator of spotted salamander embryos
 
CONSERVATION CONCERNS

Klemens (1993) felt that spotted salamanders are declining in fragmented and urbanized habitats throughout the northeastern United States. He believed the key factor influencing the species' decline is the loss of upland habitat surrounding breeding sites. Even in rural areas such a Maine, habitat loss appears to be the primary threat to the species. In Maine, vernal pools, which are often used by spotted salamanders as breeding habitat, receive little or no protection under current regulations. Portnoy (1990) documented negative impacts of acidity on embryo survival rates at extremely acidic ponds (pH 4.3-4.5) on Cape Cod. He found that reduced survival was the result of an interaction between low pH and tannin-lignin concentrations in a small number of ponds on the Cape.

In Rhode Island, spotted salamanders are relatively secure in the western and eastern parts of the state. However, as suburban sprawl takes over the state, this species will undoubtedly decline. Urbanization poses a threat to spotted salamanders for a number of reasons. First, urban areas often lack suitable breeding habitat. It is difficult to find ponds in urban areas such as Providence. Where they do exist, they tend to be permanent ponds with established fish populations, making them undesirable habitat for most pond-breeding amphibians, including A. maculatum. Second, many streets in urban areas represent dispersal barriers to adult and metamorph spotted salamanders. Most streets in urban areas tend to have high traffic volume, even on stormy nights in the spring and throughout the summer. Road mortality can be severe in these areas and must impact populations. Third, pollution from urban areas could impact populations, either as the result of runoff from roads or people discarding chemicals directly into ponds. Finally, ponds with hydroperiods (the preferred breeding habitat for spotted salamanders) represent ideal habitat for exotic fish to be introduced. Although we have never documented exotic fish introductions in ponds that were formerly fish free, we believe this is one of the potential threats to pond-breeding amphibians in the region.

NEXT SPECIES