Final Comprehensive Conservation Plan - U.S. Fish and Wildlife ...

Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
4.12.4 Introduced Reptiles and Amphibians
About 27 species of reptiles and amphibians have become established on the Hawaiian Islands. In
spite of this number, the impacts of these nonnative species in island ecosystems are generally
understudied (Sin et al. 2008). Several species of nonnative reptiles and amphibians exist in
substantial numbers on the Island of Hawai„i and may have the potential to threaten native
ecosystems such as the Hakalau Forest NWR.
Coqui Frogs (Eleutherodactylus coqui)
The coqui frog, endemic to Puerto Rico, was unintentionally introduced to Hawai„i in the late 1980s
through the nursery industry. This frog measures about 1 inch long. The back of the coqui ranges in
color from light to dark brown, while its belly is white to yellow. The frog can survive between sea
level-4,000 ft and is primarily spread by humans translocating infested vegetation. The current
distribution of the coqui frog encompasses 250 populations on all four main islands; however, the
largest concentration occurs on the Island of Hawai„i, where the frog has infested about 10 mi 2 based
on 2007 estimates (HISC 2007). In certain areas of Hawai„i, the coqui frog has reached densities of
50,000 frogs per acre (Sin et al. 2008).
In contrast to other nonnative reptiles, the coqui frog has received an ample amount of attention
because its loud mating call has adversely impacted the economy of Hawai„i (Kraus and Campbell
2002). This loud “Ko-KEE” call is produced only by the males and is most vocal after sunset and
during rainfall. Research has found that they consume a large amount of small invertebrates,
especially insects. They have been observed eating invertebrates on vegetation at night and in the
litter during the day. This generalist predator species has been found to eat about
350,000 invertebrates per 2.47 acres each night (Staples and Cowie 2001, Sin et al. 2008). Although
the coqui primarily consumes nonnative insects, they could also reduce endemic invertebrate
populations in Hawai„i.
Indirect impacts are also observed. The presence of coqui frogs lowers herbivory rates by decreasing
the amount of herbivorous insects. Coqui have also been shown to increase nutrient cycling rates by
increasing concentrations of several nutrients, increased leaf litter decomposition rates, and
increasing the number of new leaves on an invasive plant species. This acceleration of the nutrient
cycle could negatively affect slow-growing native plant species while giving nonnative species a
competitive advantage (Sin et al. 2008).
Although coqui studies have not been conducted at the KFU, frogs may potentially be on the Refuge.
Coqui frogs are known to occur at high numbers at the nearby Waiea Transfer Station (Ball, pers.
comm.).
The Coqui Frog Working Group is a partnership of various agencies and organizations that conduct
ongoing coqui frog research and control. This group includes the University of Hawai„i, Big Island
Invasive Species Committee (BIISC), Hawai„i DLNR, Hawai„i Department of Agriculture, County
of Hawai„i, Hawai„i Island Economic Development Board, USDA, and the Service. Extensive
research has been done on a wide variety of surfactants, registered insecticides, pharmaceutical
products, and food additives that could be used to control frogs. Originally, coqui frog control was
Chapter 4. Refuge Biology and Habitats 4-93