Animals with a Loud Voice (1): Gunther's Frog

Published on 6 October 2020 

We humans communicate through spoken words, while animals communicate with other members of the species by making different calls. Some animals can make a very loud call even they are small in size. Have you ever encountered these animals with a loud voice?

When you go near streams or ponds in the parks during spring and summer, you may encounter one of the animals with a loud voice - Gunther's Frog. Gunther's Frogs are common in Hong Kong. Being amphibians, they can be found in streams, ponds and wet agricultural land.

Video: Gunther's Frog is croaking

Why do Gunther's Frogs croak so loudly? Because spring and summer are their breeding seasons and the males have to sing aloud to attract the females. They need to warn off occasional intruding males, too. To perform the attractive masculine calls, male Gunther's Frogs have evolved a specialised body part. In the video, you can see when the male frog croaks, he closes his mouth and inflates the two balloon-like "vocal sacs" under the mouth.

How does a Gunther Frog make a sound?
1. Mouth closed and air expelled from the lungs
2. The expelled air passes through the larynx and vibrates the vocal cords, thus the sound is produced
3. The air finally blows up the vocal sacs, and the sound produced by a vocal cord is emitted out from the vocal sacs

The vocal sacs are as elastic as a balloon, so they recoil and deflate after a croak. The air quickly refills the lungs and with this breathing technique, Gunther's Frogs can croak for a long time. In addition to facilitating the croaking, the inflated vocal sacs also enhance the male's visual attractiveness to the females.

In nature, as each species of frog has a distinct croak, scientists have recorded their croaks to plot the acoustic spectrograms to analyze how the frequencies change with time. These data are useful in ecological surveys and related scientific research. Next time you hear the croaking frogs, other than listening appreciatively, you may record the croaks with your smartphone. Try analyzing the croaks with free apps and comparing with other sounds. Discoveries are waiting for you!

Acoustic spectrogram of Gunther's Frogs' croaks

The vocal sacs under the mouth of a male Gunther's Frog inflate when croaking