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Male Wood Frogs Calling

Usually it’s your ears that tell you that Wood Frogs (Lithobates sylvaticus) have emerged from hibernation.  They are one of the first amphibians to announce themselves, often appearing before snow and ice are completely gone.  Male frogs congregate in shallow ponds and vernal pools, where their ardent courtship ensues.

Unlike most frogs, which have a single vocal sac below their mouth, Wood Frogs have two paired sacs, called paired lateral vocal sacs, located on either side of their body just behind their head (see photo). With their mouth and nostrils are closed, male frogs pump air back and forth from their lungs to their inflated vocal sacs which vibrates their larynx and produces a duck-like quacking sound.  The vocal sacs act as resonating chambers, amplifying the frogs’ calls so as to attract females from far and wide.

Vocal sacs serve a dual purpose for some frogs. As soon as the eggs of Darwin’s Frog (Rhinoderma darwinii), found in Chile and Argentina, hatch, the male scoops the tadpoles into his mouth and they spend the next six weeks metamorphosing inside his vocal sac.  The male does not eat until the tadpoles have matured into adults and exited his mouth.

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12 responses

  1. Ben Smoke

    Excellent; wondering much about frogs now in early spring. Thank you.

    April 6, 2020 at 7:48 am

  2. Kathy Bales

    6 weeks in his mouth!

    On Mon, Apr 6, 2020, 6:35 AM Naturally Curious with Mary Holland wrote:

    > Mary Holland posted: ” Usually it’s your ears that tell you that Wood > Frogs (Lithobates sylvaticus) have emerged from hibernation. They are one > of the first amphibians to announce themselves, often appearing before snow > and ice are completely gone. Male frogs congregate i” >

    April 6, 2020 at 8:00 am

  3. Whoa! I love learning about animal dads that play an essential role in caring for their young! But wait! If he doesn’t eat for all those weeks, what about nourishment for the little tadpoles? And are you saying that they emerge as tiny frogs with legs, and functioning lungs instead of gills?

    April 6, 2020 at 10:13 am

    • Yes, the tadpoles live off the nourishment of their eggs (which the father scooped up), and do develop inside their father’s sac to full adults!

      April 7, 2020 at 12:11 pm

  4. Bill on the Hill

    Hi Mary… I’m waiting with bated breath to begin hearing my aquatic friends down below at the pond. Not so much as a peep as yet up here on the mountain, however the ice is now in the center with about 8′ of water exposed all the way around. If today warms up enough I wouldn’t be the least bit surprised to hear some early signs of the chorus that in all eventualities will become a crescendo of music!
    Bill… :~)

    April 6, 2020 at 10:14 am

  5. kathiefive

    Sounds good right about now to hole up in a safe place with a bunch of siblings!

    April 6, 2020 at 11:58 am

  6. Alice

    That’s such amazing info about the Darwin’s Frog. I wonder how the Frogs ‘thought of doing that.’ Genetic knowledge?

    April 6, 2020 at 5:35 pm

  7. Alice

    I’ve been hearing lots of Peepers for the past 2 days (south of Boston)) …I love the sound. We have lots of water around us.

    April 6, 2020 at 5:37 pm

  8. I heard them today in the hills above Plainfield. I’m curious as to how they know I was approaching the pond and quickly jumped aside and became absolutely quiet?!

    April 6, 2020 at 8:20 pm

    • I know! They see me coming from a mile away — maybe not a mile, but a good distance! I honestly don’t know if they see or hear me, but I’m guessing they see me. Five minutes of my quietly sitting there assures them I’m no threat, and their quacking resumes. 🙂

      April 7, 2020 at 11:13 am

  9. Scott Ellis

    Check out this cool video I shot inspired by this post.

    April 8, 2020 at 8:16 am

    • Great post, Scott! Sometimes those poor mobbed females actually end up drowning when kept under water by enough male suitors!

      April 8, 2020 at 4:46 pm

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