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Vernal Pools

Wood Frogs Mating

4-23-18 mating wood frogs2 0U1A0777Wood Frogs have emerged from their hibernacula and migrated to their ancestral woodland breeding pools, or vernal pools, to sing (males), mate and lay eggs (females). A chorus of duck-like quacking reveals where these hidden temporary bodies of water are located. The male Wood Frog in this photograph is on top of a female, grasping her behind her front legs in a hold referred to as “amplexus.” They will remain in this position until she lays her eggs and he then fertilizes them externally. Note that even though he has attracted a female and is in the process of mating with her, the male is continuing to sing (one of his two vocal pouches is inflated on the near side of his body).

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Vernal Pool Obligate Species

3-15-17 vernal pool IMG_4814This is the time of year when vernal pools become a main attraction for certain breeding amphibians and invertebrates. Most of these ephemeral wetlands, due to evaporation and transpiration, dry up during part of the year and therefore cannot support a population of fish. This makes them a highly successful breeding environment for creatures that need water in which to reproduce, for both they and their eggs stand a much better chance of surviving without predatory fish.

Vernal pools attract certain species of amphibians and invertebrates that are completely dependent upon these pools for parts of their life cycle (obligate species). In much of the Northeast these include wood frogs, spotted salamanders, blue-spotted and Jefferson salamanders, marbled salamanders (southern N.E.), eastern spadefoot toads (southern N.E.), vernal fairy shrimp (southern N.E.) and knob-lipped fairy shrimp (northern N.E.). If you discover a woodland body of water that has one or more of these species breeding in it, you have found what is technically referred to as a vernal pool. (Photo insets clockwise:  Wood Frog, upper right; Blue-spotted Salamander by E. Talmage; Spotted Salamander)

The next Naturally Curious post will be on 4/18/17.

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Young Wood Frogs Getting Land Legs

7-1-16 young wood frog 104

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With the dry weather we’ve been having, there is reason to be concerned about vernal pool residents, especially those that need to undergo metamorphosis before the pools dry up.  Granted, those amphibians such as Wood Frogs and Spotted Salamanders which transform into terrestrial creatures have evolved to have very quick life cycles, due to the temporary nature of their aquatic environment, but were they quick enough this year?

A very young Wood Frog crossed my path yesterday and answered that question for me.  No bigger than a raisin, it had to have emerged from its aquatic home in the very recent past.  When you think about the changes that have to occur between egg stage and adulthood (a total of two months, and it takes three of those eight weeks for Wood Frog eggs to hatch), it is mind-boggling.  Gills disappear and lungs develop, tail is absorbed, legs develop, mouth widens, intestines adapt to a herbivore-to-carnivore switch in diet – all inside of five weeks.

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“Big Night” Hazard

big night 2016 IMG_7612Every year in early spring on a rainy night spotted, blue-spotted, Jefferson and four-toed salamanders, wood frogs, and spring peepers leave their leaf litter and subterranean winter hibernacula and migrate to their ancestral breeding pools to mate.  Sometimes there are roads between these two sites.  Vehicles driving these roads inevitably kill thousands of salamanders, wood frogs and spring peepers every year.  Concerned citizens have set up teams to try to scoop up these nocturnal travelers and escort them to the side of the road in which they were headed.  While this action definitely helps, it is hard to find enough generous volunteers to man every crossing on every road all through a rainy night.

In Monkton, Vermont, Jim Andrews, Steve Parren and Chris Slesar, along with the Lewis Creek Association and the Monkton Conservation Commission, spear-headed an effort this past year to do something about the mortality of hundreds of migrating frogs and salamanders. Grants, plus a large number of organizations and citizens, provided the manpower and finances to construct two concrete culverts under a road in a location where the road separates the breeding pools of amphibians from their upland wintering grounds.

In the past, hundreds of migrating amphibians were killed in this location by automobiles during every spring and fall amphibian migration, and it is doubtful whether the population would have been able to sustain itself over time. (In the past month, 673 salamanders and 329 frogs have safely passed through the tunnel.  In addition, a few early migrators (16) have already started coming back up hill.) Hopefully, these will be the first of many such culverts in the Northeast. For further information on the Monkton underpasses, go to:  http://www.burlingtonfreepress.com/story/news/2016/03/28/hundreds-saved-new-vermont-salamander-crossing/82336084/.  (photo:  spotted salamander)        

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Spotted Salamander Spermatophores

4-23 spotted salamander spermatophores 058After male spotted salamanders emerge from hibernation and arrive at their ancestral breeding (vernal) pools, they cluster in groups called congresses, await the arrival of females, pair up with one and then the pair performs a courtship dance.

Unlike some species of amphibians, the male spotted salamander does not fertilize the eggs as the female lays them. Rather, she collects his sperm into her body and internal fertilization takes place. When the female is sufficiently stimulated, the male deposits up to 80 spermatophores (pyramid-shaped plugs of mucus with a sperm capsule at the top), often on a submerged branch. The male maximizes the chances of insemination by depositing many scattered spermatophores, covering every spermatophore he encounters, even his own, with a new spermatophore. In so doing, he increases his spermatophore count, while simultaneously eliminating a rival’s spermatorphores. The female then crawls over a spermatophore and positions her vent, or cloaca, so as to allow the lips of her cloaca to detach the sperm capsule.

Within a short period of time the salamanders retreat back to the woods, rarely to be glimpsed until next spring’s breeding season. (Photo: spotted salamander spermatorphores, with sperm capsule missing on far left spermatophore)

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Wood Frogs Awakening and Thawing

4-17-14 wood frog IMG_1377The duck-like quacking of recently-emerged, courting wood frogs is slightly miraculous considering that only days ago these amphibians were frozen practically rock solid. At some point in late fall or winter, as temperatures drop, they flood their bodies with blood sugar that acts as antifreeze in their circulatory system. Activity in their brains stops, their heart stops, and 45 – 60% of their body can freeze. Yet within hours of being exposed to the spring’s warming temperatures, wood frogs thaw out and start moving towards a body of water to breed.

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Spring Peepers Emerging

4-8-13 spring peeper2 IMG_7463Sitting on top of the snow, still as a statue, a spring peeper gathers strength to make the long trek to open water, where, if it is a male, it will exercise its voice for the first time in many months. Like the gray treefrog and wood frog, spring peepers can freeze as solid as a rock for several months during hibernation and then, on a warm day, thaw out in a few hours and resume a normal, active life.  The formation of glucose and ice crystals that form outside of cells enable this phenomenon to occur.  Once hibernation has come to an end, peepers seek out wetlands, vernal pools and ponds to breed and lay eggs before they return to their home on the forest floor.