Microhylids or Narrow-mouthed toads are represented by three species in Costa Rica.
They are probably best known by their loud buzzing vocalizations, to me reminiscent of a motor running at a high RPM, or a propeller plane moving by. Following periods of heavy rains microhylids will come to ponds and puddles to breed, to lay eggs.
Frogs as a group try to avoid ponds with fish. These are creatures which will eat the eggs young. While bodies of water will offer some advantage to eggs and tadpoles, they do not ensure safety to the adults which congregate at them and advertise their presence.
(Gastrophryne pictiventris) calls from the water surface, the frog to the left is holding on to a pond side leaf, while calling outward. Perhaps as a defensive measure, the calls of one male, run into and overlap others. Making it difficult to pinpoint the individual vocalist.