Coqui frogs (Eleutherodactylus coqui) are firmly established in Hawaii. This small, nocturnal amphibian is native to Puerto Rico but has become a major invasive species across the Hawaiian archipelago. The male coqui is famous for its distinct, two-note call, which gives the species its common name. The frog thrives in Hawaii’s warm, wet climate due to the absence of natural predators. The coqui’s presence has created significant challenges for local residents, the environment, and the economy.
The Coqui’s Arrival and Current Distribution in Hawaii
The introduction of the coqui frog to Hawaii was an accidental event, traced back to the late 1980s. The frogs or their egg masses likely arrived hidden within shipments of imported nursery stock, such as potted plants, primarily from Puerto Rico or Florida. This method of transport explains why initial populations were often found in and around plant nurseries on the islands.
The first major infestation sites were identified on Hawaii Island (the Big Island) and on Maui. Genetic analysis suggests there were at least two separate introductions that established the initial populations. The conditions in Hawaii, including abundant moisture and a lack of native amphibian predators, allowed the coqui populations to explode rapidly.
Hawaii Island has the most dense and widespread populations, particularly on the wet, eastern side. Maui also has a significant number of established infestations, making eradication unlikely on both of these islands. The coqui has also spread to the islands of Oahu and Kauai.
The spread continues to occur through human-assisted transport, as the frogs are adept at hitchhiking in vehicles, construction materials, and inter-island plant shipments. Inter-island transport remains a major concern, as officials work to prevent the establishment of dense, uncontrollable populations on the less-infested islands.
Ecological and Economic Impacts on Hawaiian Ecosystems
The presence of the coqui frog has generated a host of problems, with the most immediate being extreme noise pollution. A single male coqui’s call can reach volumes between 80 to 100 decibels (dB) at close range, comparable to a running lawnmower. Since the chorus begins shortly before sunset and continues until dawn, this incessant noise often causes sleep loss for both residents and tourists.
The high population density poses a considerable threat to the Hawaiian ecosystem. In some parts of Hawaii Island, populations have reached an estimated 55,000 to 91,000 frogs per hectare, which is more than double the density found in native Puerto Rico. These dense populations consume huge quantities of insects, potentially altering the food web.
Coquis prey on native arthropods, including spiders and insects, and compete directly with endemic insectivorous birds for food resources. Their presence can also alter nutrient cycling processes in native forests by consuming vast amounts of invertebrates in the leaf litter.
Economically, noise pollution has translated into measurable financial losses for property owners. Studies show that the presence of coqui frogs is correlated with a reduction in property values. The combined damage to real estate values across the state has been estimated to be in the millions of dollars.
The floriculture and nursery industries have also suffered. Customers are hesitant to purchase plants that may be infested, and quarantine restrictions have impacted the ability of nurseries to export plants to uninfested areas. The economic impact extends to tourism, as the relentless nighttime calling negatively affects the visitor experience and accommodation revenues.
Strategies for Management and Eradication
Management efforts are prioritized based on the level of infestation, with eradication being the goal on less-affected islands. On Hawaii Island and Maui, where populations are widely established, the focus has shifted to long-term control and containment. State and local agencies employ a variety of physical and chemical methods to combat the spread.
The most common chemical control method involves applying a citric acid solution, the only product currently labeled for coqui control in Hawaii. Since frogs breathe through their skin, the citric acid, typically sprayed at a 16% concentration, is fatal upon contact with adults, juveniles, and egg masses. A 3% hydrated lime solution is also used as a chemical treatment effective on the ground.
Chemical applications are often conducted at night when male frogs are actively calling to better target the animals. Physical removal techniques, including hand-catching, are practical for small, newly discovered populations. Habitat modification is also encouraged to make properties less frog-friendly, such as removing large, dead leaves and thinning out dense understory vegetation where coquis hide and nest.
To prevent the spread, strict quarantine protocols are in place for inter-island transport of nursery materials, construction supplies, and vehicles. Community awareness campaigns encourage residents to inspect plants and materials for frogs or egg masses before moving them. These sustained management efforts aim to protect less-colonized islands and maintain a quality of life in affected areas.