Frog hearing and communication

Sound communication

Behavioral ecology

Frogs are more often heard than seen, and other frogs (and researchers) rely on their calls to identify them. Depending on the region that the frog lives in, certain times of the year are better for breeding than others, and frogs may live away from the best breeding grounds when it is not the species’ mating season. During the breeding season, they congregate to the best breeding site and compete for call time and recognition. Species that have a narrow mating season due to ponds that dry up have the most vigorous calls.

Calling strategy

Male-male competition

In multiple frog species only males call. Each species has a distinct call, though even among the same species, different dialects are found in different regions. Although humans cannot detect the differences in dialects, frogs distinguish between regional dialects. For example, male bullfrogs can recognize the calls of their direct territorial neighbors. By ignoring the calls of these neighbors, they save energy, and only vocalize aggressively in response to an intruder's call. In this way, calls establish territories, but they also attract females. Males may have a solitary call for times when there is no competition that uses less energy. During other times, when a frog must compete with hundreds or thousands of other frogs to be heard, together they perform a chorus call where each frog calls in turn, successively. The most important feature of the chorus is the shared pattern. Through this pattern, few individuals calls are drowned out. One frog's call may be dominant and trigger the calls of the responding frogs in symphony. Calling is linked to physical size and females may be attracted to more vigorous calls. Frogs in the same region chorus within their species and between different species. Frogs of the same species will retune their frequency so it is distinct from other frogs of the same species. Different species of frogs living in the same region have more dramatically different call frequencies. The frequency and durations of different species' calls vary similarly to the preference of that species' females. The neural circuitry of females of different species varies.

A frog which demonstrates vocalizations in male-male competition is the Lithobates clamitans aka the Green Frog. Typically, they have four types of calls each warning a different level of urgency and each being distinct. The first two calls are types of advertisement calls to establish dominance among the challengers. The other two calls are more directed towards agonistic encounters.

Male-female interactions

Like the males, females can distinguish the minute differences between individual frogs. However, males and females are attuned to different parts of the advertisement call. For example, males of the onomatopoeically named coqui species are more attuned to the low frequency co part of the call, whereas females are more attuned to the high frequency qui. In fact, the order of the parts does not matter. Similarly, for females of the Tungara species, the female basilar papilla is biased towards a lower-than-average “chuck” portion of a male call. Experiments that measure the vocal responses and approaches shows these attenuations.

Mode of sound communication

Calls are often sent through the air, but other mediums have been discovered. Some species call while they are underwater and the sound travels through the water. This is adaptive in a region with multiple species competing for air time. Narins has found female frog species that use solid surfaces, such as blades of grass and logs, upon which they tap rhythmically to attract mates. Also, Feng, Narins and colleagues have found that some species of frogs use ultrasound.