Spacing and calling in Pacific tree frogs, Hyla regilla

Calling male Pacific tree frogs space out more than if they were distributed at random on the available calling sites. When new frogs are added to an area that is already occupied by some calling males, fewer additional frogs call than in a control situation where frogs are added to an empty area. This shows that behavioral interactions between frogs limit the number that call in a local area. A further experiment showed that the mating call played through loudspeakers is sufficient to inhibit additional frogs from calling. We conclude that calling leads to spacing out, which in turn limits the density of calling frogs in a local area.