Ambystoma gracile
Northwestern Salamander

Ambystoma gracile range from southeastern Alaska along the Pacific coasts of British Columbia, Washington, Oregon, Vancouver Island, to northern California (Mendocino). (Petranka, 1998)

These salamanders inhabit humid sites within dense forests and open grasslands. Adults are often found beneath rotting logs, leaf litter, and debris along stream banks. As members of the "mole salamander" genus Ambystoma, most of their time is spent underground. They are most frequently seen during fall rains and spring migrations to their aquatic breeding sites, which are usually temporary ponds with no fish presence. The larvae also reside in these ponds until metamorphosing. (Petranka, 1998; Romansic, April 23, 2001)

Aquatic adult Ambystoma gracile grow to approximately 13 cm in snout-vent length and 26 cm in total length. They typically exhibit olive-green or brownish colorations. The ventral coloration ranges from dark gray to pale white. Larvae have long, thick gills, an extended dorsal fin, and relatively long toes.

Terrestrial adults are about 14-22 cm in total length. Often, they have blotches on the dorsum and may have yellow flecks along the sides. These salamanders have a smooth brown or dark brown dorsal coloration and light brown ventral skin. There is an area of swelling behind each eye due to the parotoid glands. This feature is uncharacteristic of other Ambystomids, and resembles the condition on old world salamanders of the genus Salamandra. A glandular ridge forms a rounded tip on the dorsal tail; the distal portion of the tail is sharply tapered. In some instances, terrestrial individuals have irregular, small, light-colored blotches on the dorsum. Both aquatic and terrestrial males become darker than females during the breeding season. Unmetamophosed adult males have hypertrophied feet and hind limbs, less spots, and an enlarged glandular ridge on the tail. (Petranka, 1998; Romansic, April 23, 2001)

Embryonic periods typically last 2-9 weeks, depending on ambient temperatures. After emerging, hatchlings experience rapid growth due to an abundance of accumulated food items in the pond. Larvae in lowland populations tend to grow faster than those at higher elevations. Young A. gracile measure 50-90 mm after 1 year. These salamanders transform the following spring at the ages of 12-14 months. Metamorphosis generally begins at 50 mm total length. Some A. gracile reproduce while still exhibiting larval features, such as gills. These salamanders are known as neotenic. The majority of salamanders, however, does not stay in water and becomes sexually mature during their second year of life on land. (Petranka, 1998; Romansic, April 23, 2001)

Breeding occurs once yearly. Pairs are always monogamous in that once a female takes a spermatophore inside her body, the eggs are fertilized. However, new mates are selected randomly every year and selection depends on the performance of a mating ritual. (Petranka, 1998)

Breeding takes place in both permanent and semipermanent bodies of water. Migration to these areas occurs during the transition from Winter to Spring (January-April, depending on latitude).

Upon contact with a potential mate, the male salamander dorsally mounts the female and stimulates her with his chin and tail. Afterwards, the male swims a short distance away and deposits a spermatophore package (a solid, airtight conglomeration of sperm). If breeding interest still exists, the female will follow. The male salamander then stimulates the female in a behavior similar to a tickle as she inserts the spermataphore into her cloaca to fertilize her eggs. It should also be noted that other mating rituals have been observed, including stereotyped attempts at insertion of the spermatophore by the male. Always, this behavior fails, and the spermatophore is picked up by the female and inserted into the cloaca.

Eggs are deposited between January and May and are typically attached to rooted aquatic vegetation. The salamander larvae emerge after approximately one month, but may take as many as nine weeks to hatch. Hatchlings measure 8 mm in snout-vent length. (Petranka, 1998)

Eggs are typically deposited in a habitat devoid of predatory fish. All of the salamanders evacuate the pond shortly after the breeding season, leaving the eggs in the water until hatching. (Petranka, 1998; Petranka, 1998)

Ambystoma gracile generally live five years. (Petranka, 1998)

In the aquatic form, A. gracile are generally diurnal, foraging on insect larvae during the day. In populations where fish predators are present, a shift between optimal patch use and predation avoidance seems to occur. Animals in this habitat are typically nocturnal and inhabit vegetated areas for protection.

On land, adults live in the abandoned underground burrows of other animals, or under rotten stumps, lose bark, etc. They are typically nocturnal and emerge from hiding after a rainfall, possibly to forage on worms and larvae forced up by flooding.

When alarmed, this species becomes aggressive and secretes a poisonous milky substance from glands in both the posterior part of the head and lateral portions of the tail. As an aggressive measure, the salamanders will smear the poison on an attacker with the tail. In a typical threat posture, the animal will close its eyes, lower its head, and defensively raise the tail over the body. (Petranka, 1998; Romansic, April 23, 2001)

There have been few studies on the density characteristics of A. gracile, so the home range has yet to be quantified.

When molested these salamanders may give off a ticking sound and assume a defensive posture. As nocturnal hunters, much of the salamanders' perception of the world relies on smell. Airborne scents are picked up with the olfactory system. After a general direction is identified, the vomeronasal system tracks minute scents on the ground, leading the animal towards its target. (Petranka, 1998)

In lowland populations of British Columbia, these salamanders catch and consume soft-bodied invertebrates such as annelids, mollusks, cladocerans, ostracods, amphipods, anostracans, isopods, copepods, mites, dipterans, and a variety of other insect larvae.

Larval salamanders consume aquatic annelids, aquatic arthropods, and small mollusks. (Licth, L. E., 1973)

Studies have shown that predation on larval salanders can drive a population towards extirpation. It was found that predatory trout in breeding locations has reduced both average snout-vent length and recruitment, which has caused a narrowing of local population densities. The presence of trout has also correlated with a decrease in total body mass of the larvae by driving them into sub-optimal habitats to forage. (Nussbaum, et al., 1983; Romansic, April 23, 2001)

In some areas, juvenile A. gracile provide food to aquatic predators. On land, they also function as important members of the trophic pyramid by consuming invertebrates and in turn are preyed upon by larger organisms.

This species can also serve as an indicator of environmental degradation. Salamander eggs can only hatch in clean, fresh water with little UV radiation. A drastic decrease in salamander numbers can signal a change has occurred within the ecosystem. (Nussbaum, et al., 1983; Romansic, April 23, 2001)

Aside from their contribution to the biodiversity of northwest US forests, A. gracile is not a species of economic importance.

Ambystoma gracile do not negatively impact humans. If, by chance, an animal was consumed by a person, its poisonous skin secretions would likely cause sickness.

Road development is a major threat to the breeding migrations of salamanders. They fragment the habitat and put the animals in danger of car mortality. Moreover, research suggests that A. gracile prefer to inhabit old-growth forests, which are heavily harvested in many areas. Placing a forest buffer of 200-250 m around breeding sites used by terrestrial adults will help in preserving current populations. Finally, the introduction of trout to a water system previously devoid of large predators can severely weaken the salamander population in the surrounding area. (Romansic, April 23, 2001)

Limb regeneration is a phenomenon that occurs in this species. Tissue in the remnants of the limb regenerate nerve fibers, and the new limb bud slowly emerges and forms.

Ambystoma gracile is commonly referred to as the northwestern salamander, or is divided into two subspecies, the brown salamander, Ambystoma gracile gracile (found in the southern portion of the range), and the British Columbia salamander, Ambystoma gracile decorticatum (found in the northern range). (Licth, L. E., 1973; Petranka, 1998)