While staff at the Tennessee River Gorge Trust wait for the arrival of neotropical migratory birds in spring, did you know there is evidence of an entirely separate terrestrial migration happening this winter right at our feet? Specifically, the breeding migrations of spotted salamanders (Ambystoma maculatum) is in full swing. Spotted salamanders are found across much of the eastern United States in hardwood and mixed mesic forests near available aquatic breeding sites, usually seasonal, fishless wetlands. They belong to the genus Ambystoma, a group of mole salamanders that also include the marbled salamander (Ambystoma opacum) and aptly named mole salamander (Ambystoma talpoideum), both residents throughout the TN river gorge. Like other terrestrial mole salamanders, spotted salamanders spend most of their juvenile and adult life in underground burrow systems or under moist cover objects. Data compiled from the Virginia Herpetological Society document burrow systems of individual adults exceeding over 12m² of the forest floor! When environmental conditions are just right, spotted salamanders emerge from their subterranean overwintering refuge and migrate up to 200 m to aquatic breeding sites.
Make it stand out
Whatever it is, the way you tell your story online can make all the difference.
The timing of this migration entirely depends on precipitation and temperature cues and thus varies greatly throughout their range, with migration occurring as early as December in the south and as late as April in the north. Generally, when soil temperatures 30cm below the surface are above 40°F with soil temperature increasing closer to the surface, migration occurs on nights during or following rains. Sexton et al. found that 98% of all migration occurred when there was at least 4 mm of rainfall and an average 3-day temperature of 42°F for a spotted salamander population studied in Missouri over 10 years. Often referred to as a “Big Night”, mass spotted salamander migrations can tally close to 100 individuals observed visiting 1 breeding pool overnight. Volunteers of the Salamander Crossing Brigade with the Harris Center for Conservation Education in New Hampshire provided safe passage for 1,066 spotted salamanders at 35 different road crossing sites for the 2024 spring season. These volunteers counted 59 spotted salamanders crossing the road in just one night!
For more northerly populations, the breeding season can be restricted to a few days when conditions are right. Here in the south, spotted salamanders can have up to 3 major bouts of breeding migration over the course of 2 months. Once at the breeding pool, males use submerged vegetation to deposit spermatophores that are eventually picked up by females, with females frequently picking up many, making multiple paternity common in spotted salamanders. Females can deposit multiple egg masses, each containing upwards of over 100 eggs. Egg masses are either clear, milky white, or green. The milky white coloration occurs when females deposit a protein in the outer layer of the egg mass while the green coloration comes from a more unexpected culprit.
Green egg masses are an example of mutualistic endosymbiosis. Endosymbiosis is a relationship where one organism is living within the cells of another organism. A well-known example of this relationship can be seen between reef building coral and single celled algae where algae supply the coral with nutrients via photosynthesis and the coral provides a protected environment for the algae. For spotted salamander eggs, Chlorococcum amblystomatis is a single-celled green algae that invades and grows inside salamander host tissues and cells, eventually disappearing during the final larval stages of salamander development. As explained in Kerney et al.’s research, this relationship is mutualistic because the algae support salamander embryo growth and hatchling survival while the embryo supports algae population growth.
Throughout the TN river gorge, we have already found evidence of spotted salamander breeding activity in the scattered vernal pools of our landscape.
Explain where vernal pools occur, what other species use them, and what to do if you encounter eggs.
Add in house photos of spotted salamanders, eggs, and vernal pools.
Add links to research papers mentioned.
Add videos
