Friday, February 26, 2016

Going to the pool in winter (Vernal Pool)

We've had some warm and rainy February days out here at the Edge of Appalachia Preserve, and that means its time to check the vernal pools and see what kind of amphibian activity has occurred.  Vernal pools are wet places that hold water in the winter and spring, but dry up in the summer and fall.  They can be ponds in a field, roadside ditches or any depression that holds a little bit of water half the year.  If a vernal pool has been established for many years, there's a good chance frogs, toads and salamanders have used it as breeding pools for egg laying.  They choose vernal pools because they hold water long enough for the presence of food sources  (i.e. insects, amphipods etc.), but not long enough for prey species to become established (i.e. fish).
This wet field in the winter is a great vernal pool for amphibian mating
I checked a couple pools on the preserve this week to see what has been moving.  There are a few salamander species that use these pools this early and couple of frogs as well.  Scooping a net in a pool produced a few inch-long salamander larva.  Any larva that large in a pool in February would have to be that of the marbled salamander, Ambystoma opacum.  And these were indeed marbled larva.  Marbled salamanders mate and lay their eggs in September within the pool boundaries when it's waterless.  Throughout winter, as the water fills the pool, the eggs hatch and the larva start growing before any other species lays eggs in the pool.  The adult pictured below was from the fall, only larva are found in the pool in February. 
Marbled salamander (Ambystoma opacum) from September.  Larva are now swimming in the vernal pools
Also within the pool were small clumps of gelatinous eggs holding Jefferson salamander, Ambystoma jeffersonianum, larva.  I did not find any adult Jefferson salamanders in the pool, but did find an adult under a rock at the edge of the pool.  Jefferson salamanders will move to the pools to mate at the first warm (>55F) rainy nights in the winter.  I have found eggs in pools as early as December 27th.  But February is the typical time for mass movements of these salamanders.  Years ago I was doing recruitment surveys for a state herpetologist. During this survey, I (with the help of Rich McCarty TNC) counted 270 Jefferson's, and that was only what was in the traps.  I can count the thumb on one hand, and that's the number of Jefferson salamanders I have seen in the wild that were NOT in or around a vernal pool.  So if you wanted to find's the time.
Jefferson salamander (Ambystoma jeffersonianum) under rock at edge of pool
Also in February the spotted salamanders, Ambystoma maculatum, will be moving in mass to these same pools.  They are historically a little bit later than Jefferson's, but are due.  I just didn't see any this day.  All three of the salamanders mentioned above are often called mole salamanders because they spend most of their life underground.  This is why they are so hard to find, unless, you know about their breeding habits and when and where to look for the annual movements to vernal pool.
Spotted salamander (Ambystoma maculatum) found in previous years but not from this week. 
Ambystoma salamander eggs in a vernal pool.  Much smaller clump than the woodfrogs.  Clump on the left looks like it was laid much earlier than clump on the right.
I couldn't help but notice a huge mass of eggs at the end of one of the pools.  This is typical of the woodfrogs, Lithobates sylvaticus.  The weekend before, woodfrogs were calling  all over the county.  Unlike the salamanders, the early spring frogs give you a signal that the time is here.  And you can hear it from far away, leading you to these vernal pools.  In February, spring peepers, Pseudacris crucifer, and woodfrogs are the only species tolerant enough to withstand the cold temperatures before and after the egg-laying.  Both were heard calling throughout the day.  But only the woodfrog leaves the massive amounts of eggs like these shown below this time of year.
Although under water, you can still see large numbers of clumps of woodfrog eggs.  Each black dot is one egg.
Woodfrog (Lithobates sylvaticus) eggs sticking to a branch.
Many spring peepers were found in and around one of the vernal pools, but their eggs are harder to find.  They also don't have as short of a breeding period as the woodfrogs.  You can hear spring peepers calling well into April and maybe May.  Woodfrogs are true winter breeders.  They even are adapted to freeze solid and still survive.  Even if the vernal pool freezes again this year, many of the eggs are structured to survive.  The black side of each egg faces the sun to absorb heat and keep from freezing.
Spring peeper (Pseudacris crucifer) hiding in the grasses near the vernal pool.

Woodfrog (Lithobates sylvaticus)
To hear woodfrogs and spring peepers calling in one of our vernal pools, listen to the video below.  The spring peepers  are the high pitched whistles and the woodfrogs are the quacking chatters in the background.

Some of these species are very hard to find in the wild.  But if you learn the life histories of each species, you can definitely learn the tricks of where and when to look.  Finding the eggs in the pools and hearing the calls of the frogs, to me,  represent the first real signs that spring is right around the corner.  The amphibians' annual ritual of visiting these pools have created an annual ritualistic hunt for myself and many naturalist that brightens up the long gray winter.

For more information about these vernal pool species, check out Amphibians of Ohio, 2013 from Ohio Biological Survey’s website here.  This book contains an enormous amount of information about all of Ohio’s amphibians.
Posted by: Mark Zloba