It seems as if I’ve spent the last three weeks slogging about in chest high waders amongst murky waters in search of egg clusters, fairy shrimp, and chorusing wood frogs. The vernal pool season is short. The critters that utilize these mostly temporary ponds do so with little notice. And if one hoping to witness this annual miracle is not on his or her toes they just may miss one of the high points of the ecologic year.
This vernal pool year was like none other I’ve seen before in western New England. Our first rainy night without mountains of snow was on April 10th. This is a fairly near average starting dates for these parts. The drizzly night had temps in the low 40′s. Both male mole salamanders (mostly spotted salamanders) and wood frogs began their march to their breeding habitat. The males generally leave a little earlier than the females to deposit spermatophores. These little pearls will be picked up by the female mole salamanders and internalized where her eggs will be fertilized. But something went wrong that first rainy night. The females stayed put. For some reason they had no real urge to move. After the males had started their journey the temperature began to plunge. And plunge it did all the way from the mid 40′s to the mid 20′s in just a few hours. And while its pure speculation I suspect the females decided to hold off for better traveling conditions. And of course it then stayed cold, mostly at or below freezing, and did not rain at night for more than a week.
Whatever the reason my inspection of many random local vernal pools over an area of several hundred square miles revealed lots of spermatophores immediately after that first rainy evening. But a week later almost all of the spermatophores were still there. I appeared at the time if the females had simply not used them in the vernal pools that I investigated throughout the western Franklin County region.
Immediately after that first rainy night there were chorusing wood frogs. Each individual melody sounds more like a miniature bark than a song but in any event the power of the chorus lies in sheer numbers. At every vernal pool there were hundreds of wood frogs celebrating the breeding season. Their song, a little rough around the edges and certainly not nearly as sweet as spring peepers, was loud, clear, and a little overwhelming. And sure enough a few days later submerged logs and vegetation were shrouded with wood frog eggs. It was by any measurement a good season for wood frogs!
But the breeding success of the mole salamander was a different story. Ten days after the first rainy night revealed that there were still large numbers of spermatophores dotting the wet detritus at the bottom of the vernal pools; many in obvious states of decomposition. And while I did find occasional mole salamander eggs, obviously suspended and appearing as a solid gelatinous mass that resembles clear Jello that holds black spots within the jelly mass, there were very few. This became critically clear at one vernal pool where typically hundreds of egg masses can usually be located. After slogging around within its several acre wet perimeter for an hour I managed to locate only five. This pattern held up in nearly all the vernal pools I visited. And so it appears this would almost certainly be an unsuccessful mole salamander breeding season for much of the region.
But like much of nature vernal pools are remarkably resilient. Mole salamanders can live for a couple of decades so the notion of one not very successful breeding season would likely put a dent in one year of an age class rather than the entire population. Like many issues in the natural world failure is as expected as success. Perhaps something we humans should understand and take into account when it comes to our own endeavors.
Life cycle stories around vernal pools seem to abound from the mysterious to the glorious. Vernal pools are unique habitats that hold success for a handful of creatures. Without them the natural world would be both less diverse and less interesting. Perhaps my favorite story about vernal pool creatures involves the wood frog.
Unlike many creatures that are dependent upon weather and climate for body temperature (what used to be commonly referred to as “cold blooded”) wood frogs do not dig themselves below the frost line in the soil as winter approaches. These critters have a unique and miraculous ability to survive temperatures many degrees below zero (Fahrenheit) through some pretty interesting body chemistry adaptations. When winter approaches the wood frog simply bury their bodies underneath a thin layer of leafy material. As the cold weather approaches wood frogs use an interesting combination of chemical conversions that allows their bodies to freeze without fatal results.
Like many other reptiles, amphibians, and birds wood frogs excrete their waste in the form of uric acid. Uric acid does not dissolve in water. As the air temps fall below freezing the wood frog begins to accumulate and concentrate uric acid in their tissues. At the same time this tiny frog starts the process of changing sugars (glycogen) to glycol, basically an anti-freeze, and distributing this throughout their body. The glycol and uric acid serve to keep ice from forming within the inside of cells of the frog’s body. As the cold weather gets serious and these little guys begin to freeze water goes from the inside of the frog’s cells into its inner body cavity. The water surrounds the major organs and the uric acid and glycol prevents the small amount of water that remains inside the cells of the frog’s organs from freezing. However the water that now engulfs the organs freezes solid.
To the best of my knowledge no other amphibian, reptile, mammal, or bird can freeze solid and remain alive. These wood frogs can stay frozen for months and when the right time comes begin thawing from the inside out and upon complete thawing come back to life. During this frozen state the frog does not breathe, the heart does not beat, and there is no known brain activity! This is so effective that the wood frog is the only amphibian or reptile to be found north of the Arctic Circle.
This process sounds like something in a science fiction book but is very real. By the way, although humans have a fundamental idea how this process works we have not been able to replicate it. The exact mechanisms that employ the chemical conversions are not fully understood. The possibilities for utilizing this wonderful adaptation are as varied as the human imagination. Imagine how suspended animation would aid space travel!
Another miracle of vernal pools involves an interesting symbiotic relationship between the eggs of the spotted salamander and a particular species of green algae. Spotted salamander eggs are surrounded by a thick gelatinous mass. This dense jelly mass provides wonderful protection for the eggs as they develop into larvae however it is so dense that it keeps oxygen from penetrating the mass. The larvae need to breathe oxygen through their gills to survive. Fortunately there is a species of green algae that uses the jelly mass for structure, essentially a secure home where it can go about its algae-like business. The green algae uses photosynthesis to convert sunlight into sugars for food. Of course one of the primary byproducts is oxygen. This “gas of life” is available in this wet environment for the larvae to breathe through their gills. And there you have it, when least expected, a perfect relationship between a tiny green plant and a salamander larvae. How wonderful is that!
And what about the relationship between such strange bed fellows as vernal pools and bobcats? Many years ago I discovered quite by mistake that bobcats frequent vernal pool sites during their late February and early March breeding activities. It seems that they like the open spaces amongst the thick cover of trees created by the vernal pools. This is so reliable that I have encouraged organizations I work with to set up trail cams along the edges of vernal pools in hopes of getting some good bobcat photos. During late February while working with The Trustees of Reservations (TTOR) we were doing some winter tracking. A set of bobcat tracks led us to a vernal pool where the tracks met up with another set of tracks. We could see that the cats were rolling around, an unusual behavior for the normally solitary cat. The TTOR staff set up trail cams and within a month retrieved the video cards only to find some amazing photos of bobcat mating behavior!
Bears also use vernal pools in early spring. When bears wake up from their winter torpor (hibernation) they seek out vernal pools. Bears are enormously hungry after having not eaten for the entire winter. This naturally makes food the primary object on their still awakening minds. Vernal pools are amongst the first areas to produce green plants. And even more interesting black bears are not adverse to eating salamander and frog eggs either!
As this vernal pool season winds down I am not disappointed that it was not that productive for the mole salamanders. This type of occasional quirk makes me focus on the wonderful lessons that vernal pools offer all of us in understanding nature.
Think survival. Think resiliency. Think imperfections that are somehow perfect. Think about how we humans can learn by observing what surrounds us.
Originally written for Heath Herald in April of 2014.