WHY THESE FROGS ARE DEVASTATING TO HAWAI'I
Ecological attributes: Only the ecology of E. coqui has been well-studied. This species can occur in its native rain forest at densities exceeding 20,000 animals/ha (8100/acre) and consume an average of 114,000 prey items/night/ha (46,000 prey/night/acre). Densities in one nursery on Big Island probably equal or exceed this. They prey primarily on arthropods, but will also forage on snails and small frogs. E. martinicensis has similar ecological attributes to E. coqui, except for a greater toleranee for dry conditions, occurring in tropical dry forest in the Lesser Antilles. E. planirostris consumes similar, though smaller, prey items to E. coqui and can occur at high densities but probably requires warmer temperatures for survival than does E. coqui. Hence, it is unlikely to invade mid-elevation rain forest.
All three species are nocturnally active, feeding, calling, and mating at this time. E. coqui and E. martinicensis forage from the ground to up in the canopy. E. coqui and E. martinicensis call primarily from 1-2m (3-7') elevation on exposed perches. Both species hide in forest leaf litter during the day and shuttle to elevated perches at night. Preferred daytime retreats are large rolled leaves, although animals will use artificial hide boxes constructed of bamboo sections if made available.
E. planirostris is terrestrial and climbs only a few centimeters above ground level. For all species, eggs are laid in protected sites among the leaf litter, are guarded by the male parent, and require approximately 2-3 weeks to develop directly into small froglets. There is no tadpole stage and, consequently, no need for access to surface water. Generation time for E. coqui is approximately eight months, and the other two species are probably similar.
Conservation concerns: E. coqui and E. martinicensis pose the greatest threat to native Hawaiian ecosystems because they can invade mid-elevation mesic and rain forests. They can be expected to exert tremendous predation pressure on a variety of native arthropods and, possibly, snails. Consequently, they will likely exert an indirect negative effect on the remaining native forest birds, most of which are partially or largely insectivorous. The frogs may serve as an energy sink in native ecosystems into which they insert themselves due to lack of native predators, although it is more likely they will instead serve as an additional food source enhancing population levels of rats and mongooses, thereby increasing predation pressure on native forest birds.
Anthropocentric concerns: E. coqui and E. martinicensis have loud, piercing calls that often disturb people's sleep (calls of E. coqui are typically measured at 90-100 decibels at a distance of 0.5m [1.5'] from the frog). This same problem has been noted for other species of Eleatherodactylus introduced to areas outside their native ranges. Several populations of frogs have come to our attention as complaints from disturbed residents, visitors, or hotels. All of these have been for small choruses of frogs. Large choruses can be deafening but are restricted so far to a couple of nurseries.
Information last updated: May 1998. For additional information contact: Fred Kraus, Hawaii DLNR/Forest & Wildlife, tel (808) 587-0166