Ambystoma gracile
TAXONOMY
Siredon gracilis Baird, 1859, Cascade Mountains, near latitude 44° north, Oregon, United States. Two subspecies generally are recognized, although scientific evidence for this is weak.
OTHER COMMON NAMES
None known.
PHYSICAL CHARACTERISTICS
These fairly large salamanders grow to 8.7 in (220 mm) in length. They are uniformly brown or black and breed both as metamorphs and paedomorphs. Metamorphosed adults have extensive poison glands in the parotoid region and on the base of the tail; when disturbed, they often secrete a white, sticky, toxic secretion.
DISTRIBUTION
The northwestern salamander occurs in wet fir and redwood forests of northwestern North America from Sonoma County, California, United States, to British Columbia, Canada.
HABITAT
Paedomorphs of this species are most common in permanent lakes at higher elevation, whereas metamorphs tend to occur in conifer forests at lower elevations. Unlike many other ambystomatids, paedomorphs can coexist with predatory fish by shifting their activity patterns and becoming nocturnal.
BEHAVIOR
Individuals of this species spend most of their adult life in underground burrows, although they may be found on the surface during rains. When these salamanders are disturbed, they assume a rigid posture with the tail partially raised and secrete a white toxic liquid from the parotoid region of the head and from the upper ridge of the tail.
FEEDING ECOLOGY AND DIET
Larval northwestern salamanders feed on zooplankton, a wide variety of aquatic invertebrates, and frog tadpoles; larger individuals take larger prey. Terrestrial adults presumably feed on earthworms and other invertebrates.
REPRODUCTIVE BIOLOGY
Reproductive maturity is reached in two to several years, depending on elevation. Populations vary in terms of metamorphosis/paedomorphosis; it is not known whether the two types interbreed.
CONSERVATION STATUS
No obvious declines have been documented, although there may be evidence that populations are reduced in logged or secondary-growth forests.
SIGNIFICANCE TO HUMANS
None known.
