The soothing sounds of nature can often be heard at night, from the chirping of crickets to the croaking of frogs. If you’ve ever wondered why some frogs get noisy after dark, you’re not alone. Join us as we explore several frog species that vocalize nocturnally and discuss why these amphibians sound off under the moonlight.
Here’s a quick answer: Frog species like tree frogs, chorus frogs, leopard frogs, and ornate burrowing frogs are among the most common nocturnal croakers. Most advertize mates with loud calls after sundown to take advantage of calmer conditions that allow sound to travel farther.
Common Nocturnal Croaking Frog Species
Tree Frogs
Tree frogs like green tree frogs and gray tree frogs are common frogs that make noise at night. They live in trees and get their name from the suction cups on their toes that allow them to climb vertical surfaces.
When trying to attract mates, tree frogs make a barking or clicking sound during the night. The green tree frog’s call has been described as sounding like a loose banjo string. Isn’t that a colorful description?
The familiar sound of tree frogs croaking on summer nights is a comforting background noise for many people.
Chorus Frogs
As their name suggests, chorus frogs are tiny frogs that sing in big groups, creating a deafening chorus. There are several species, like the western chorus frog and Pacific tree frog. Chorus frogs gather in wetlands and damp areas near ponds and streams to call/sing their loud, raspy mating call that gets louder as more frogs join in.
A large chorus can sound like squeaky fingers rubbing against a balloon or a finger running along the teeth of a comb. How funny! But the boisterous croaking is music to potential mates’ ears.
Leopard Frogs
The northern leopard frog is a true croaker, making a snoring sound by inflating and deflating its vocal sacs. They live near water across much of North America. Males gather in large groups during spring to call for females in ponds and slow streams.
Their deep, rattling croak has been described as sounding like a chainsaw trying to start up. Yikes! But female northern leopard frogs love the sound and will approach the male making the best croak. What charming courtship! Leopard frogs continue croaking on warm wet nights through the summer.
Ornate Burrowing Frogs
One frog that truly sings at night is the ornate burrowing frog found in parts of Australia. It spends the day underground to avoid drying out and emerges at night. As darkness falls, male ornate burrowing frogs start a slow, mournful liquid trill song to attract females during mating season.
The beautiful, flute-like call sounds like glass bells and carries long distances across wetlands. Female frogs hop over to the males with the most pleasing songs. The crooning continues for hours until mating is done. Then the frogs again burrow underground as the sun rises. What dedicated lovers!
Reasons For Nocturnal Frog Vocalizations
Attracting Mates
Many frog species vocalize at night to attract potential mates. The breeding season for most frogs coincides with warmer weather, so nighttime provides the ideal conditions for projecting their calls over long distances.
Species like the Green Tree Frog use a singing mating call that can reach over a mile to Grab the Attention of females. The male’s advertisement song helps the female locate him for breeding. Some tropical frog species even form large breeding choruses with hundreds of males vocalizing together to increase their chances of Finding a mate.
Defending Territories
Male frogs often establish and defend a territory during breeding season. Their vocalizations help mark territorial boundaries and Ward Off competing males. For example, the Northern Leopard Frog produces a snore-like call to proclaim its territory.
If an intruder approaches, it will shift to an aggressive growl To drive them away. By vocally announcing their presence at night, male frogs can maintain exclusive access to resources like food, water, egg-laying sites, and potential mates within their domain.
Avoiding Daytime Predators
Many of a frog’s predators rely on vision to hunt, including birds, snakes, and lizards. Calling at night allows frogs to minimize detection. Their nocturnal activity patterns likely evolved as an adaptation to avoid these daytime threats.
Studies show that certain frog species calling more At night in the presence of predatory stimuli during the day. Their after-dark vocalizations when predators are less active improves breeding success while limiting risky daytime exposure.
Still, some nocturnal predators like owls cue in on frog vocalizations, creating an evolutionary Arms Race between predator and prey detection abilities.
Unique Adaptations For Nighttime Calling
Enlarged Voice Boxes
Many frogs that call at night have enlarged voice boxes, also known as larynges. The larger larynx allows them to produce louder, deeper mating calls that can be heard at greater distances (1). This helps attract mates across ponds or dense vegetation where visibility is low.
For example, the green frog (Rana clamitans), which breeds at night during the summer, has an outsized voice box nearly twice the size of closely related daytime breeding frogs. Its resonant deep groans can be detected over 300 meters away (2)!
Larger voice boxes require significant energy to maintain and use, so night calling frogs have evolved specialized muscles and circulatory adaptations to power their booming vocalizations (3).
Light Colored Throat Pouches
Some nocturnal frog species feature light-colored vocal sacs or throat pouches which are inflated to amplify their mating calls. The giant bullfrog of Africa (Pyxicephalus adspersus) possesses large white throat pouches that act as reflectors to help their deafening calls travel farther at night.
Studies show their white vocal pouches reflect sound waves outwards, adding up to 10 decibels of volume compared to frogs without reflective throat adaptations (4). Other frogs like the túngara frog (Engystomops pustulosus) have inflatable vocal sacs surrounded by flashes of white or light skin that likely serve a similar reflective function (5).
The light coloration contrasts against the night sky to make their vocal sac inflation and calling motions more visible to potential mates.
Ability To See Well in Low Light
To find mates at night, frogs need enhanced vision in low light conditions. Many nocturnal species have larger eyes with wider pupils to allow more light through. Some also have superior rod photoreceptor density on their retinas to detect faint light signals (6).
Certain frogs have an additional tapetum lucidum reflective layer behind the retina that bounces light back through visual pigments for a second pass at nighttime stimulation (7). Some frog eye adaptations rival those of strictly nocturnal animals like owls or cats.
For example, the red-eyed treefrog (Agalychnis callidryas) relies on excellent dim light vision to hunt insects after sunset. Its large protruding eyes with vertical slit pupils provide sensitivity down to mere starlight illumination (8).
Superior low light vision combined with loud calls allows frogs to effectively find mates after sunset when many predators are less active.
Impacts and Threats to Nocturnal Frog Species
Habitat Loss
Habitat loss is a major threat to nocturnal frogs. As forests and wetlands are cleared for agriculture, housing, and industry, frogs lose their homes. According to one study, over 50% of wetlands in North America, Europe, Australia and China have been destroyed since 1900 (1).
This drastic habitat loss leaves frogs more vulnerable to predators, pollution, and climate fluctuations.
Pesticides and Pollution
Chemical pollutants like pesticides, fertilizers, and industrial chemicals are extremely harmful to frogs. These contaminants leach into wetlands and waterways, poisoning frogs and their food sources. One staggering study found that Atrazine, a common herbicide, can turn male frogs into females!
(2) Other pollutants weaken frogs’ immune systems, making them more susceptible to diseases like chytridiomycosis.
Climate Change
Rising global temperatures threaten frogs in several ways. Higher temperatures increase evaporation, leading to drier habitats. Paradoxically, climate change also increases extreme rainfall events, which can wash away frog eggs and tadpoles.
Plus, frogs are ectotherms, meaning they rely on external temperatures to regulate their body heat. As things heat up, their delicate thermoregulation is disrupted.
Invasive Species
Non-native animals and plants often outcompete native frog species when introduced into their habitats. For example, the American Bullfrog has been driving out local frogs from wetlands across North America with its voracious appetite (3).
Other invaders like the Cane Toad poison native predators with their toxic skin secretions. With no natural defenses against these foreign invaders, frogs struggle to survive.
References:
(1) https://www.sciencedirect.com/science/article/pii/S0006320718313636
(2) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2842049/
(3) https://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=1717
Conclusion
The choruses of amorous amphibians that serenade us on warm nights provide a soothing soundtrack to nature. While frogs like tree frogs and chorus frogs vocalize after dark to attract mates, other nocturnal croakers defend territories and avoid daytime predators.
Unique adaptations help these resourceful ribbiters call loud and clear in darkness. Sadly, many frogs are threatened worldwide by habitat loss, climate change, and pollution. Protecting wetlands and reducing pesticides are vital for preserving the delightful evening concerts of frogs.
The next time you hear frogs sounding off under the stars, take a moment to appreciate their intricate nightlife. With a bit of ecological awareness, we can ensure our croaking companions continue to vocalize through the ages.
