The Hawaiian Islands host numerous amphibians today, but none are native to the archipelago. The islands did not naturally host any frogs, toads, or salamanders. Several non-native species have established permanent populations following human introduction, primarily resulting from global trade and human movement. These introduced species, particularly a notoriously loud frog from the Caribbean, now inhabit diverse ecosystems across the main islands.
The Absence of Native Hawaiian Amphibians
Hawaii’s unique biodiversity developed in extreme isolation, positioned nearly 2,400 miles from the nearest continental landmass. This vast ocean expanse created a powerful biological filter, making natural colonization difficult for most terrestrial life forms. Amphibians, due to their permeable skin and reliance on moisture, are especially vulnerable to saltwater and desiccation, making the journey across the Pacific nearly impossible. The pre-human colonization rate was estimated to be as low as one successful new species establishment every 25,000 to 50,000 years. The islands’ terrestrial ecosystems evolved without amphibians, creating an ecological gap. Consequently, the native fauna does not include any frogs, toads, or land reptiles, meaning every herpetile encountered arrived via human transport.
The Coqui Frog: Hawaii’s Noisiest Invasive Species
The most widely known frog in Hawaii is the Puerto Rican Coqui (Eleutherodactylus coqui), a small, nocturnal tree frog and widespread invasive species. It was accidentally introduced around 1988, primarily arriving as stowaways in shipments of nursery plants and other cargo from the Caribbean. Initial introductions occurred separately on the Big Island and Maui, allowing populations to expand rapidly.
The Coqui is a small amphibian, typically tan to dark brown, with adult males reaching a maximum snout-vent length of about 50 millimeters (2 inches). They are identifiable by large, rounded toe pads that allow them to ascend vegetation. The Coqui uses direct development, where eggs hatch directly into tiny froglets without a tadpole stage, bypassing the need for standing water.
The frog’s common name comes from the loud, distinctive two-note mating call produced by the male, which sounds like “ko-kee.” This vocalization begins at dusk and continues until dawn from elevated perches. This constant, high-volume chorus is the primary reason the Coqui is considered a severe pest species.
Ecological and Economic Impacts of Introduced Frogs
The extremely high population densities achieved by the Coqui frog pose significant threats to the local ecosystem and human communities. Hawaiian populations can reach densities up to 91,000 frogs per hectare, two to three times higher than in their native Puerto Rico. This population explosion is attributed to the lack of natural predators and competitors.
Ecologically, the Coqui is a voracious, generalist predator that consumes vast quantities of native invertebrates, including insects and spiders. Dense populations can consume approximately 40,000 invertebrates per square meter nightly, significantly altering leaf-litter and aerial invertebrate communities. This predation pressure creates direct competition for food sources with native insectivorous birds, disrupting the native food web.
The most immediate impact on human life is the intense noise pollution created by the male’s call. Individual calls have been measured to reach sound levels between 80 and 100 decibels. This noise level far exceeds the state health standard of 70 dBA, leading to sleep deprivation for residents and tourists.
This acoustic nuisance also generates measurable economic consequences. The presence of Coqui frogs must be disclosed during real estate transactions on the Big Island. Studies have found that properties within 500 meters of a recorded Coqui complaint experience an average reduction in property value. The noise also negatively affects the tourism and nursery industries, where contaminated plants can lead to decreased sales.
Management Strategies and Other Non-Native Species
Controlling the widespread Coqui population is an ongoing challenge, particularly where they are well-established. Short-term management focuses on chemical control, primarily applying a 16% citric acid solution. The citric acid acts as a toxicant absorbed through the frog’s permeable skin, effectively killing adults and eggs on contact.
Other methods include using a 3% hydrated lime solution, habitat modification to reduce shelter, and deploying lure traps made from PVC pipe. Eradication is considered unattainable on the Big Island and unlikely on Maui, so efforts focus on containment and localized population reduction. Long-term research is exploring classical biological control, which involves introducing a natural enemy, though this requires extensive testing.
Other Introduced Amphibians
The Cane Toad (Rhinella marina) is another non-native species widespread across the main islands. It was intentionally introduced in 1932 to control sugar cane pests and is a large, diurnal amphibian that is less noisy than the Coqui.
The Greenhouse Frog (Eleutherodactylus planirostris), a smaller relative native to Cuba, is also established. This species arrived accidentally in plant shipments and is often mistaken for the Coqui. The Greenhouse Frog is less vocal, producing a faint, cricket-like chirp, and is more terrestrial, typically found under leaf litter rather than high in the canopy.