How can tiny frogs make so much noise?

This week's question comes from Karin Macaulay in Victoria, BC. She says "We have listened to a tree frog this past summer and been amazed at the huge voice from this little creature. How do they make such a loud sound? 

Sarah Schorno, an instructor in the Department of Integrative Biology at the University of Guelph says it is quite common to hear frogs calling in the springtime, looking for mates. 

Just like us, frogs produce sound by passing exhaled air over their vocal chords while coordinating the ventilation of their lungs. Frogs breathe a little differently than humans however. They bring air in through their nose by expanding the floor of their mouth. They then close off their nostrils and raise the floor of their mouth to force air into their lungs. When this air is exhaled, it flows over the vocal chords which then vibrate to produce sound. 

These sounds are then amplified by passing air into the frog's vocal sacs, which expand from the floor of the mouth to act as sound resonation chambers.

She suggests one think of a frog's vocal chords as the strings of an acoustic guitar, and the vocal sacs as the hollow body of the guitar. As you pluck the strings, they vibrate and transmit sound energy to the body of the guitar, making it and the air inside the body resonate and amplify the sound. This makes the sound considerably louder. This is similar to how even small frogs are able to make such loud sounds.