Spring's Arrival II

      April 7th was the second really warm day of spring.  In some parts of western PA it came with the first rain of spring.  As I drove down the dark back roads heading to Gettysburg, I kept my eyes alert for small amphibians.  Sure enough, I had to make a last minute adjustment to avoid a toad hopping across the mountain road at about 9:30 pm.
 

Red-spotted Newt returning to Lower Lake



     The first warm spring rains bring one of the most amazing animal events that few people know about - the spring amphibian migration.  The warmth and rain convince the amphibians it is time to mate and lay eggs.  Frogs, toads, and salamanders have been hibernating all winter.  Most of them have hibernated below ground, but the tree frogs have stayed above ground.



     This is because treefrogs have a special adaptation for surviving winter.  When the temperatures start to get cold, the frog's body produces glucose that undergoes a complicated process with adrenaline to prepare the cells in the frog for cold storage .  This natural anti-freeze protects the frog's body when temperatures drop below freezing.  Occasionally, people find tree frogs in the winter and they appear to be frozen solid.  If brought indoors, they will start to hop around after they warm up.  (However, this is probably not good for the frog - especially if its going back outside.)

     Once the temperatures warm the tree frogs, and other amphibians, start moving to wet areas to reproduce.  They tend to do this at night during a warm rain.  The rain is needed to keep the amphibian's skin moist as humidity levels this time of year can be very low.

Lower Lake filling

      Amphibians migrate to ponds, lakes, wetlands, and vernal pools.  The latter are small ponds that dry up in the summer - so they don't have the aquatic predators that ponds and lakes have.

     At  Lutherlyn, spring peepers and American toads congregate at the lower lake.  This lake is drained each winter to reduce plant growth and keep it safe from swimming.  As a result, there aren't any fish looking for a frog, toad, or tadpole snack.  Schools that visit on overnight field trips get to experience the frogs and toads congregating at Lower Lake.  By May 15th, the shallows of the lake are usually filled with small tadpoles.

      The tadpoles grow fast and usually are leaving the lake by the first week of summer camp (the third week of June).  The first weeks of summer camp mark the secondary amphibian migration as very tiny frogs and toads leave the water and disperse throughout Lutherlyn.