Croaking is one of the most common noises made by frogs. On warm, rainy nights, it’s common to hear the croaking choruses of hundreds of frogs coming from ponds or other freshwater bodies nearby. But have you ever wondered why frogs seem to start and stop croaking at the same time?
Frogs start and stop croaking at the same time to reduce the risk of an individual frog being singled out by a predator. A single frog croaking stands out and can be easily located by birds, snakes, and many other predators. However, many predators will have a harder time finding one frog from a chorus of hundreds of calling males.
Attracting the attention of predators is a real danger when frogs call for mates. Many predators have learned to locate frogs by listening in to their mating calls (more information on that is below).
Why Frogs Croak
Frogs croak to attract mates. The typical loud croaking calls that we hear frogs make are known as advertisement calls- it’s male frogs advertising themselves as potential partners, hoping that female frogs will like their song and come their way.
These distinctive sounds range from high-pitched peeps to full-throated croaks.
Males usually call from ponds, swamps, streams, and other possible breeding sites.
When females are ready to mate, they will move towards calling males, and pick the male that they prefer.
In some frog species such as the barking tree frog, most females will mate with the male closest to them. This is especially more likely when the distance to other calling males is large.
However, in many species, females can be much more selective. Some species prefer males who make their calls longer and more frequent – and other species prefer males who call next to a pre-made nest.
Every frog species has a sound that is unique to their species – and the croaks of some species can be heard over a mile away!
Female frogs will only be attracted to the call of their own species
Frogs Synchronize Croaking to Reduce Predation
When male frogs croak, female frogs are not the only ones listening – many predators are also drawn to the calls. Many predators such as birds and snakes are also drawn to the croaking.
For example, Túngara frogs, found in Middle, Central, and South America, are often preyed on by bats which locate them by homing in on their mating calls.
In addition, flies called midges, find their way to Túngara frogs by “intercepting” their mating calls. Midges feed on the blood of the frogs but also carry diseases and parasites, which they frequently transmit to frogs.
To reduce the risk of predation, many frogs have learned to call in large synchronized choruses.
As earlier mentioned, a single frog croaking stands out and can be easily located by predators. However, many predators will have a harder time finding one frog from a chorus of hundreds of calling males.
If you ever take time, to approach an area where you hear a croaking frog, you will probably notice that the frog stops croaking when it notices you get closer. It’s a behavior to ensure that the frog stays hidden when a predator is around.
Some Frogs Avoid Croaking Entirely, to Avoid Predators
Individual males of some frog species, such as the American green tree frog (Hyla cinerea) go to even greater lengths to avoid predation.
They avoid croaking entirely, and choose to remain silent when looking for mates (these are called ‘satellites’).
Instead, these frogs will intercept the calls of nearby males, and mate with approaching females. This is known as “sexual parasitism“.
Doing this enables satellite males to conserve energy, and avoid attracting the attention of predators.
Some Frogs Mainly Croak at Night, to Avoid Diurnal Predators
The majority of frog species are either nocturnal or crepuscular and are most active at night or in the low-light hours right before the sun rises and sets.
Although many frogs will croak during the day, the croaking choruses typically intensify on warm nights, especially after a rainy day.
The darkness of the night means frogs are less vulnerable to predators such as hawks, and eagles that are strictly diurnal and don’t hunt at night.
Frogs also blend into their environments easier to hide and avoid active predators in the cover that the darkness provides.
Croaking Is Not the Only Sound Frogs Make
Although most people are familiar with frogs’ mating calls (loud croaking), frogs can can make a variety of other sounds, for different functions.
1. Territorial calls
In the mating season, male frogs often form temporary territories to attract females, which they defend from other males. These territories usually occupy the immediate area around an individual.
Breeding male frogs will defend the boundaries of their territories, and scare off other males by using a variety of calls. Some frogs will even fight intruding males.
Research has shown that male frogs of many species can tell the difference between their established neighbors, and unfamiliar strangers. This helps them avoid aggressive encounters with male frogs that hold territory nearby.
Female frogs choose their mates in part by the quality of their call, and their ability to defend their territory.
2. Distress Calls
Many frog species can make “distress calls” when they are grasped by a predator. This call is usually a high-pitched scream that startles a predator causing it to release the frog, enabling the frog to escape.
3. Release Calls
Another type of vocalization is made by frogs that have been unwillingly grabbed by another frog searching for a mate, these are known as release calls.
When a male frog tries to mate, he may attempt to grab onto any frog that is close to him. If he grabs onto another male frog, a female that has already mated, or a frog of a different species, the grabbed frog will emit a release call – telling the offending male to let go.
The sound of the release call can be different depending on the frog species. In Green tree frogs (Hyla cinerea) the release call sounds somewhat similar to the soft clucking of a chicken. These calls are also sometimes made by the frog if it is being held too tightly in your hands.
4. Warning Calls
Another vocalization in some frog species is a “warning call”, a noise that is made by a frog that has been startled or disturbed. The frog may make a short squeak as it leaps away.
Like other frog vocalizations, warning calls can be different depending on the frog species.
In green frogs (Lithobates clamitans), the warning call is an abrupt iCUP! In American bullfrog (Lithobates catesbeianus), the warning call is a loud eeek!
Conclusion
Frogs vocalize for a variety of reasons, but the most common and well-known type of vocalization is the mating call.
When frogs croak and call for mates, they are in danger of being spotted by predators. For this reason, they developed several strategies to increase their survivability.
One of those strategies is to call in large choruses, making it harder for potential predators to single out any individual frog.
Sources:
Erhard, H. C. (1994). The Evolution of Vocalization in Frogs and Toads. Annual Review of Ecology and Systematics, 25, 293–324. http://www.jstor.org/stable/2097314
Emerson SB, Boyd SK. Mating vocalizations of female frogs: control and evolutionary mechanisms. Brain Behav Evol. 1999;53(4):187-97. doi: 10.1159/000006594. PMID: 10343085.