The 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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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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Although 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.)
The peeps of male Spring Peepers can be heard fairly consistently this time of year. Unlike in the spring, these calls are coming not from bodies of water, but from the woods nearby. And they are single peeps coming from individual peepers, not the chorus of “sleigh bells” one hears in the spring. This phenomenon occurs so regularly in the fall that herpetologists have given it a name – “fall echo.” They speculate that the calling of peepers is spurred by light and temperature conditions, when fall climate conditions are similar to those of spring.