The rest of the year, they are rather shy, and you rarely see them. But in Spring, especially in April, they croak.
The big bubbles the toad inflate on their cheeks betray them, although their color matches perfectly the water lilly pad they are seated on.
Their choir is not continuous. It sounds all of a sudden in the silent air. One frog starts, and quickly all the other ones reply, louder and louder. After a minute or two, they stop briskly.
I suppose they believe they sung harmoniously and are waiting for the applause of the visitors walking around Claude Monet’s pond.