Bullfrog chorus

On our walk by the Rideau River yesterday evening we stopped to find out what a group of people were staring at over the wall by the tennis courts in Stanley Park. (50-60 years ago, this wall used to be one side of a swimming pool in the river, the Flat Rock Pool, also called Les Trois Piscines.)

The answer was bullfrogs, lots of them, sitting on the weeds in shallow water and making their distinctive noise. One of the human crowd was croaking in imitation; probably a mating call, we warned him. Looking carefully, we could see these large and rather ugly frogs blowing out the air sacs in their neck as they made the calls. Someone said that they eat smaller frogs; I hadn't known that.

This is how they sound: