The Evening Chorus

As the light fades over the pond, the frogs start calling. This male has both vocal sacs fully inflated, two grey balloons puffed out at the corners of his mouth.

Why frogs call

Calling is mostly a male activity. Males call to attract females during the breeding season and to tell rival males where their patch is. In a busy pond, dozens of frogs can join in at once, and the chorus can carry a long way on a still evening.

Two built-in amplifiers

Water frogs have paired vocal sacs, one on each side of the mouth. When the frog calls, air is pushed back and forth between the lungs and the sacs, and the stretched membranes act like resonators, making the call louder than such a small animal could manage on its own.

Working in the last light

Dusk is when calling is most intense, but also when light is running out. Shooting from water level and keeping the frog against a brighter patch of sky or water helps the vocal sacs stand out.