Female black (pond) frog (Pelophylax nigromaculatus) during certain periods They make strange soundsin which only males reside/jump near they hear.
In such cases, they want to communicate that they are either not fertile at the moment, or they are not in the mood for a full-on fight with male frogs. This is important because, says Makoto M. Itoh of Nagoya University in Japan:
Male black spotted frogs jump on anything that looks like a female, including inanimate objects.
Therefore, females have to find a way to drive them away when they are not in the mood or unable to do so.
In general, males make more vocalizations just to get a female’s attention and let them know they’re interested in her — and in their reproductive capabilities.
However, Ito discovered a few years ago that black-spotted females produce simpler, shorter, and lower-pitched sounds than males. They live with these if they do not want or cannot reproduce.
Makoto M. Ito conducted a series of experiments on frogs to discover the purpose of soft female voices and was able to determine whether the signals were real. Females only release them if they have no eggs to fertilize, or if they have no eggs at all. One is not enough, but if they vote twice, then the males understand that there is no place and time for mating here.
