Triggers to the Salamander Breeding Migration

Defining approximately when the salamanders will be on the move is pretty simple. We need warm weather to melt the snow and some rainy nights. But trying to define what triggers the salamanders' mass migration is a bit more involved. Even in the early 1900's, biologists were recording the dates that the salamanders first appeared, trying to figure out what makes them move.1 More recently, Sexton et al., measured conditions at which a majority of all migration occurs and outlined guidelines2. These conditions are listed below;

Primary Condition

Secondary Condition

These conditions were defined in Missouri and we decided we would collect related data in our locality and see how it measures up. In 2003 the USC set up a permanent monitoring station at a pool that hosts a large breeding population of both Spotted Salamanders and Jefferson Salamanders in the watershed. The station included a rain gauge and digital logger, soil and air temperature logger, and water temperature logger. The data collection units are entirely automated and the digital loggers can be downloaded as often as needed or as little as once a year. Rainfall in measured continuously throughout the year. The soil temperature is measured at 2 cm and 30 cm along with the air temperature. These are recorded every half hour on a multi-channel digital data logger. Similarly the water temperature in the pool is continuously measured throughout the year.

Drift fence and pitfall traps have been constructed around the pool for monitoring animal movement to and from the pool. Monitoring of the traps is done throughout the breeding season. We keep detailed records of all amphibian movement that can be linked with the monitored conditions. From that data we have created some graphs for the past few years for Jefferson and spotted salamanders.

Dates of initial salamander immigration.

Trying to exactly predict the triggers to migration is difficult. There are many factors that can influence the timing. Some years there is more or deeper frost than others. Some years there is heavy snow over virtually frostless ground. We've witnessed Jefferson salamanders digging up through 8 inches of wet snow to get to a pool with only the slightest water open around the edges. I have also sat at the pool on a completely dry night, following an afternoon thunderstorm and listened to hundreds of salamanders crunching through the leaves to get to the pool.

We will continue to collect data and maybe one day we will be able to be more precise. But for now, once the snow is gone and we get a few warm days, that first rainy night that follows should be exciting. We encourage others to get out there and spend the nights at the pool. Experiencing it for yourself, witnessing things that aren't written in text books, this is what makes it exciting. This is what makes it the “Big Night”