Salamanders make pond pilgrimage

Posted on March 07, 2008 by Suzanne Ramsey

Well, it’s happened again and almost like clockwork, too. On March 4, only a couple of days later than last year’s event, Sweet Briar’s population of spotted salamanders made its annual migration to Guion Pond.

The 8-inch long, yellow polka dotted amphibians — commonly described as “cute” — travel to the pond each year to breed. As biology professor Linda Fink has said, “Once a year, they doodle over to the pond, have sex for a week and come back.”

For the other 360-some days of the year, the salamanders live in the woods behind Guion Science Center, eating earthworms and bugs. On the first warm, rainy day of the year — the “salamander rain” — they emerge from their burrows and make their way to the pond.

The males arrive first and deposit spermatophores on the bottom of the pond. When the females arrive, they “internalize” them, Hayslett explained, by picking them up with their cloaca, the combined opening of their digestive, urinary and reproductive tracts. After fertilization, the females lay their eggs and leave the pond with the next rain.

“Salamander sex is kind of bizarre,” Hayslett said. “There’s no physical contact between the male and the female and yet there’s internal fertilization. It’s kind of different.”

Conditions were right for the mass exodus on March 4, with the weatherman predicting a 60-degree day with torrential rain, thunder and even a tornado watch.

According to SBC naturalist-in-residence Mike Hayslett, the thunder may act as an alarm clock for the little creatures. “Some say it’s an auditory cue,” he said before last year’s event. “The rumbles and vibrations might be a signal to bring them up.”

For the second year in a row, Sweet Briar students, most of them in the ecology and field natural history classes, documented the migration. Before the night was over, they had captured, weighed and marked 636 salamanders — an increase of nearly 80 over last year’s total.

Hayslett attributed the difference to knowing the slippery creatures a little better. In 2007, spotters were scattered throughout Guion Woods to capture the critters, but halfway through the evening, scads of salamanders were found emerging from an unmonitored creek bed adjacent to the dam.

“Last year, they came out of the dam and we missed a lot,” he said.

This year, students were assigned to the area and found salamanders erupting from the creek bed like a “Texas tea.” Hayslett, standing on top of the dam with a net, predicted the final total would “knock our socks off.”

Another change in the operation involved the way the salamanders were marked for future studies. In 2007, the “Twitty” method was used, which involves clipping one of the salamander’s toes.

This year, a visible injected elastomer that fluoresces in ultraviolet light was used. Ecology teaching assistant Sara Rothamel ’09 called the method “more reliable,” and said using the VIE eliminates the question of whether a toe was removed or lost accidentally and it lasts the lifespan of the animal.

Students also counted, weighed and marked the salamanders in tents set up around the pond rather than carry them in buckets to the biology lab in Guion. This move sped up processing and, according to Hayslett, “reduces the stress and interferes less with [the salamanders’] progress.”

Sweet Briar’s dean Jonathan Green was one of several faculty members who showed up during the event, either to lend a hand or observe. “I came down here to see my students being students,” he said. “The salamanders are cool, too. Twenty-year-old scientists being scientists. It’s especially cool when they can tell me something about them.”