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Wood Frog

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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Amphibians Migrating

3-6-17-spotted-salamander-2-img_7608Vermonters were witness to a record-breaking (early) amphibian migration in the Champlain Valley last week on March 1st, when night temperatures were in the low 50’s.   Not only did it occur a week earlier than any other previous major migration, but records show that migration for the earliest amphibians in Vermont is now approximately two to three weeks earlier than it has been during the last decade. (as reported by Jim Andrews, www.VtHerpAtlas.org).

Spotted Salamanders, Four-toed Salamanders, Eastern Red-backed Salamanders, Blue-spotted Salamanders, Jefferson Salamanders, Spring Peepers, Wood Frogs and even an American Toad were on the move. According to Andrews, “this is a concern if the weather turns really cold and the ground and ponds refreeze. If that happens, many of the early migrants (that are not freeze tolerant) could freeze and die. If the weather stays relatively mild, with only short cold snaps, they should be fine.” Weather since these sightings has been unseasonably cold, and one can only hope they survived. (Photo: Spotted Salamander, Ambystoma maculatum)

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Green Frogs Mating & Laying Eggs

6-14-16  green frogs 008The loose banjo string call of the Green Frog is a familiar sound near wetlands this time of year.  Males (to the right in photo, with bright yellow throat) have been busy serenading females (to the left in photo, with white throat), in an attempt to breed with one.  Female Green Frogs select their mate, a choice which is based partially on the suitability of the male’s territory (underwater plants are a plus).  After inspecting several males’ territories at night, the female chooses one and slowly approaches him, turning to face away from him as their bodies come in contact.  External fertilization takes place as he clasps her while she lays her eggs (known as “amplexus”).

Unlike Wood Frog eggs that are laid in clumps, or Spring Peepers’ individually-laid eggs, Green Frog eggs are laid in a loose cluster that often floats on the water’s surface (see photo) or is draped on underwater plants.  Each cluster usually consists of 1,000 to 5,000 eggs that hatch in three to five days.  Females sometimes return to breed a second time with a different mate, in which case the second egg clutch is usually smaller, consisting of about 1,000 to 1,500 eggs.

The larval, or tadpole, stage of a Green Frog lasts from 3 to 22 months, which explains why you might have already seen large Green Frog tadpoles this summer.

(Outstanding theories were submitted on yesterday’s mystery. Be sure to read comments!)

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Wood Frog Egg Matts

wood frog egg mass IMG_2760Now that normal spring temperatures have returned, the air around vernal pools is once again filled with the clacking/quacking calls of male wood frogs hoping to attract females. Once this has been accomplished, most paired wood frogs head to the same general area in the pool to mate.  The resulting egg masses, each consisting of several hundred eggs, form a communal cluster, or “egg matt,” on the surface of the water.  Eventually algae will start growing on the jelly-like substance surrounding the eggs, causing them to resemble pond slime – an effective camouflage.  The gelatin covering, the size of the communal cluster, and exposure to the sun all help the eggs to be warmer than the surrounding water and they develop quickly – a necessity if one is to metamorphose into an adult before the vernal pool dries up.

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Effects of Cold Weather on Breeding Amphibians

4-5-16 peeper on snow IMG_7453 With spring peepers (pictured) and wood frogs just coming into voice, and some salamanders also having recently emerged from hibernation, there is concern for their welfare due to the erratic weather we are having.  According to Jim Andrews, Director of the Vermont Reptile and Amphibian Atlas, the effects of this meteorological fluctuation depend on the exact climatic conditions experienced, as well as the species affected.

Wood frogs and spring peepers, as stated in a recent post, are well equipped to survive the cold weather.  However, egg-laying has already taken place in some locations and if the eggs are exposed to the air, as opposed to being attached to a submerged branch or vegetation, and it’s cold enough, long enough, they will freeze.

Many of the mole salamanders, including spotted, Jefferson, and blue-spotted, are in the middle of migrating to or from their annual breeding pools.  Faced with freezing temperatures, they retreat temporarily into the leaf litter and thawed soil beneath, a sheltered environment where they spend all of their life except the breeding season.  An extended period of cold that freezes the ground would pose problems for these creatures, although Andrews has witnessed the survival of a blue-spotted salamander that sought shelter under rocks that were on top of frozen ground.

Many factors are involved in the effects of this phenomenon  – how warm it was before the cold spell arrived (long enough for hibernating amphibians to emerge?), how low temperatures go, how long it remains cold, the species of frog or salamander, and where it is in its breeding cycle.  The peeping and quacking we briefly enjoyed has been silenced, but not permanently and hopefully not for very long.

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Wood Frogs & Spring Peepers On The Move

3-29-16 road frogs 015Although the temperature hovered around 32°F.  last night in central Vermont, wood frogs and spring peepers were on the move.  Usually it is above 40° or 45° before you see the earliest of our breeding amphibians, but a few hardy souls ventured forth to their breeding pools and ponds under cover of darkness and  rain yesterday.  Those that breed in vernal pools are in a hurry to take advantage of every day, as the eggs they lay must complete metamorphosis by the time their pool dries up, often in mid- to late summer.

Both of these species of frogs are freeze tolerant.  Wood frogs are coming out of a state in which they haven’t taken a breath and their heart hasn’t beaten for several months.  Prior to hibernation they convert glycogen in their bodies into glucose, a form of antifreeze that helps prevent the water within their cells from freezing, which would kill them.  However, the water outside their cells does freeze.  Amazingly, wood frogs can survive having up to 65% of this water frozen, yet when warm weather arrives, they thaw and move about in a matter of hours.

If you rescue these woodland amphibians that are crossing roads (where so many of them get run over at night) during their migration to their breeding pools, take note of the temperature of their body.  Often they are still quite cold to the touch — colder than the air, even – which fortunately makes it difficult for them to move fast enough to escape your helping hands. (Photo: Amorous wood frogs getting a head start as they cross a road to get to breeding pool.)

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Spring Peepers Peeping

12-16-15 spring peeper IMG_7853The sound of a peeping Spring Peeper in December (yes, this occurred in Vermont this week) conveys to one and all that climate change is not a figment of our imagination. Amphibians are extremely sensitive to small changes in temperature and moisture due to their permeable skin and shell-less eggs. Certain species, including Spring Peepers, Grey Tree Frogs, Wood Frogs, American Bullfrogs and American Toads, are emerging and mating earlier in the year than they did historically. Causal relationships have been found between irregular climate conditions (drought, increasing frequency of dry periods and severe frosts) and decreasing (extinction in some cases) of certain amphibian species.

Behaviorally and physically, warming temperatures are having an impact on amphibians. A recent laboratory study investigated changes in amphibian metamorphosis time due to pond desiccation and whether amphibian immune systems become compromised as a result of these changes. They found that amphibian immune responses became increasingly weaker and white blood cell counts were increasingly lower with higher desiccation. As a result of climate effects, immune systems are weakened, making it more difficult for amphibians to fight off diseases.

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