A pond full of frogs can become surprisingly loud after dark.
The noise is mostly communication.
For many frog species, males call to attract females and warn rival males.
Male frogs produce most mating calls
The exact sounds vary by species.
Females can use the calls to identify members of their own species and evaluate potential mates.
That is important when several frog species are calling in the same area.
The vocal sac amplifies the sound
Many frogs have an expandable vocal sac under the throat.
Air moves between the lungs and the vocal sac while the frog calls.
The sac acts like a resonating chamber.
It makes a small animal much louder.
Why do frogs call at night?
Many frog species are more active after dark.
Nighttime can reduce heat and water loss.
It may also provide safer conditions from some predators.
Calling when females are active makes biological sense.
Why do frogs call after rain?
Rain creates moist conditions frogs need.
Temporary pools and wetlands may fill.
Breeding opportunities increase.
That is why a wet night can suddenly sound like every frog in the county has discovered karaoke.
Do frogs call only for mates?
No.
Different calls can signal territory, distress, or other information.
The nighttime chorus shares the same broad communication problem as fireflies using light signals, although frogs solve it with sound instead of light.
But mating calls are the source of much of the familiar seasonal chorus.
Is this like bird song?
Broadly, yes.
Both can use sound for mate attraction and territorial communication.
But frogs produce the sound with different anatomy from birds chirping in the morning.
The pond chorus is mostly frogs broadcasting relationship and real-estate information.
And that’s the short explanation.
Related explanations: Why do birds chirp in the morning?, Why do fireflies glow?, and Why do moths fly around lights?