| what | when | where | pic |
|---|---|---|---|
| wood frog, rana sylvatica | 2010-04-22 | near gunhouse street, near moose hill, sharon |  |
| gray tree frog, hyla versicolor | 2010-04-22 | near gunhouse street, near moose hill, sharon |  |
| spring peeper, pseudacris crucifer or hyla crucifer | 2010-04-22 | near gunhouse street, near moose hill, sharon |  |
April 22 was a warm rainy night in mid-spring, and while driving home at around 8 pm Jennifer and I noticed that the roads were filled with enthusiastic little hoppers. Strangely enough, we did not hear the peepers trilling away in our backyard, even though we have a little pool there and plenty of foliage; we had heard them earlier this spring. Perhaps the extra moisture meant that the spring migration in our backyard did not depend as much on rain?
The frogs and toads have a problem. Large lakes are filled with predatory fish and other ravenous monsters. Little ponds are too small to support these predators, but the frogs and toads can’t live in them because shallow water is liable to freeze through during winter. What’s a little amphibian to do? Here’s their solution: they overwinter in large lakes, when it’s already cold enough that the predators have shut down for winter. In spring, when things are getting dangerous in these bigger volumes because of predatory re-animation, they migrate en masse to wetlands, with cozy little puddles and ponds. There, they feast on the insects that similarly love these waters, and they breed. This migration always happens on a wet and warm night in spring, and that’s what we were watching. I believe the phase of the moon may be relevant, too, but am not sure (I’ve read they prefer dark nights). For the record, April 22 was close to the first quarter. This may mean the moon phase is not important, or it may mean that we missed the main migration and witnessed a secondary one.
We went out again later at night to investigate this more thoroughly. The original frogs were seen on Gunhouse St., which is near Lake Massapoag and near a set of woods, but I don’t know of any vernal pools in the area (which doesn’t mean there aren’t any — most places in Sharon are near some vernal pool or the other). The most frogs we saw in any one place were on Harold St., off Gunhouse. Strangely enough, Harold isn’t particularly close to any woods that I know of. I don’t understand why the density was highest there. But it is true that the trilling of the peepers seemed strongest there.
In a short time, we counted five or six different frogs. Interestingly enough, they were strongly varied sizes, and at least three different species, not that closely related: Spring peepers ; the gray tree frog, hyla versicolor; and the wood frog, rana sylvatica. I would guess that the main reason for the migration at the same time is that there really aren’t all that many choices for warm (but not too warm, or the aquatic predators would be out), rainy, dark nights in early to mid spring — and not the herd effect, of safety in numbers. It would be interesting to confirm this, though. Can they sense that the others are migrating, and does it spur them to migrate too, like geese calling in fall? It is certainly interesting that so many different species made the same decision on the same night.
We took photos. First the wood frogs, rana sylvatica.
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| From insects and spiders |
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| From insects and spiders |
Next, the spring peepers. Take a look at their claws, although they’re not very good in these photos: they can climb trees.
This one was tiny — probably less than an inch:
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| From insects and spiders |
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| From insects and spiders |
And now the gray tree frog:
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| From insects and spiders |
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| From insects and spiders |
We then drove to the Moose Hill Audubon Center, where we saw several more, making about ten for the night.
Then, there’s the dog that didn’t bark: we saw no salamanders or newts. I’ll try to look out for them especially this summer. Hopefully we’ll see some. I know Akash asked me tonight to go on the salamander watch, and I had to tell him I had dropped the ball on that.
[POSTSCRIPT: As you can tell in the comments below, this article has been substantially rewritten from what it was originally, on the advice of Alex Hall. Thank you for your help, Alex! I’m a little embarrassed how bad the previous identifications were, but this is my first time!]
a little wild 
That second frog species is Hyla versicolor, the Gray Tree Frog. Although their colors are highly variable, if you had the chance to pick it up, you would have noticed bright yellow spots on the undersides of its joints. They’re really hard to spot unless you hear them calling – good find!
Thank you very much. I appreciate the correction! Since the colors are highly variable, can you tell me how to make the identification?
For me, the most obvious visual cue is the blotchy darker color (usually dark gray) on a background of lighter color (usually light gray) where the darker color is outlined by a darker color still. The yellow patches on the underside are the giveaways, but generally that requires picking them up.
I’m more of a frog call expert, and the male advertisement calls are very distinct. In fact, there’s two almost indistinguishable species of gray treefrog: Cope’s Gray Tree Frog (Hyla chrysocelis) and the Gray Tree Frog (Hyla versicolor). H. chrysocelis has two sets of chromosomes (diploid) and H. versicolor has four sets of chromosomes (tetraploid). If you catch a pond during their breeding season, you might be able to tell the difference between the two species based solely on their calls. H. chrysocelis has a call rate that’s about twice that of H. versicolor and resembles a buzz more than the chuckle of H. versicolor.
Thanks for asking – I love answering herp questions 🙂
Also, now that I’m looking at the photos more carefully, your first two photos are Wood Frogs (Rana sylvatica). They can be easily identified by the mask around their eyes and their dorsolateral ridges. They’re really common up north and when I was up in Michigan I saw them crossing the roads almost every night.
You definitely ID’d the Spring peepers right, though. The cross on their back is what gave them their scientific name (Pseudacris crucifer; also called Hyla crucifer).
So many different frog species in one night! Very nice.