Earthsky Interviews
Private: Alien Frog
02-04-2002 - Biodiversity
_JB:_ On the island of Puerto Rico, tiny tree frogs called “coqui” are a much-loved national symbol. But coqui have found their way to Hawaii, and some people aren’t too happy to see them.
_DB:_ A species of coqui got there as accidental stowaways -hidden in potted plants that were imported for landscaping. Scientists think that, in some places, Hawaii might have as many as 8,000 coqui per acre. A frog population that size can eat nearly 50,000 insects a night . . .
_JB:_ And that’s bad news for Hawaii’s native insects and the native birds that depend on them for food. What’s more, Puerto Rican tree frogs also have big voices. Their chorus can be loud as a lawnmower. Some resort owners think that it’s bad for tourism because guests have trouble sleeping through the nocturnal call of thousands of singing frogs.
_DB:_ Biologists are working on ways to control coqui without harming other creatures. One idea is to drench potted plant soil with hot water. Meanwhile, in Hawaiian forests, pesticide experts have been known to spray infested areas with concentrated caffeine – and possibly induce a cardiac arrest in coqui.
_JB:_ Our thanks today to the “U.S. Forest Service”:http://www.fs.fed.us/ and to the “National Fish and Wildlife Foundation”:http://www.nfwf.org/. We’re Block and Byrd for Earth and Sky.
The following individuals were interviewed for today’s show. Our thanks to:
Earl Campbell
USDA National Wildlife Research
Hilo, Hawaii
Fred Kraus
Department of Natural Sciences
Bishop Museum
Honolulu, HI
The following web sites and articles provided information relevant to this script:
Campbell, E. A., F. Kraus, S. Joe, L. Oberhofer, R. Sugiara, D. Leaseand, P. Krushelneycky. “Introduced neotropical tree frogs in the Hawaiian Islands: Control technique development and population status.” Paper presented at “Eradication of Island Invasives” Conference, Auckland, New Zealand, February 19 – 13, 2001. Kraus, F.,? E. Campbell, A. Allison, and T Pratt. “Eleutherodactylus frog introductions to Hawaii.” Herpetological Review 30 (1): 21 -25 ;1999.
The website of the “Hawaii Ecosystems At Risk project”:http://www.hear.org/frogs (HEAR). Hear coqui calling and print out your own frog poster.
An article by Rod Thompson, “”Isles’ Frog Infestation is an Earful”":http://starbulletin.com/2001/07/29/news/story3.html, of the Honolulu Star-Bulletin July 29, 2001
A USDA “”news feed”":http://www.usda.gov/agency/oc/vtr/tv/television.htm about the frogs
“The Puerto Rican view of Hawaii’s coqui infestation”:http://www.nandotimes.com/nation/story/75344p-1060021c.html (NandoTimes.com)
Author’s notes:
On a global scale, frogs as a group are in trouble. Many species are showing rapid declines, and no cause for these declines has yet been clearly determined.
Given such widespread frog declines,? some people wonder whether killing frogs in Hawaii is a good idea. But the Puerto Rican frog Eleutherodactylus coqui (known as the coqui comun in its native Puerto Rico, to distinguish it from several other treefrogs collectively called coqui)? and its close relative the Caribbean treefrog or greenhouse frog Eleutherodactylus planirostris, are doing fine in their native habitat, and they doesn’t belong in Hawaii where the two insect-eating frogs are having a serious impact on the many rare endemic insects that have evolved on this isolated island chain.
Hawaii has no native amphibians after all, before humans invented boats and then planes, it wasn’t easy to cross the 2,500 miles of ocean that separate Hawaii from the nearest continent. Coqui aren’t the first exotic frogs to invade Hawaii bullfrogs, leopard frogs, cane toads and Chinese wrinkled frogs have been here for a while. But these species can live only where there is surface water, such as pools and streams, where their tadpoles can develop. Hawaii’s volcanic bedrock is porous, so ponds and pools are few. The invader frogs are found mostly in lowland areas, where people have dug ditches and ponds, and where the native flora and fauna are already severely disrupted.
The coqui don’t have this restriction; their eggs hatch out into full-formed frogs. Females do have to lay their eggs in water, but even a micropool, such as the water that collects in clusters of plant leaves, will suffice. So scientists are worried that the frogs will spread into higher-elevation rainforests, which currently serve as refugia for many native species.
Besides the threat to native insects, coqui pose other problems in Hawaii. They have turned out to be a new and very palatable food source for rats and mongooses, two other alien species brought to Hawaii by humans. Both rats and mongooses have had a role in the serious decline of many native Hawaiian forest birds. With frogs so plentiful as a food source, populations of these other predators may increase.
Another problem is that coqui are showing up in shipments of Hawaiian produce and plants intended for export. Other countries want to prevent the frogs from invading, so farmers whose orchards have been infested risk having their shipments destroyed, or losing their export permits.
IN early October 2001, after careful consideration, the U.S. EPA gave preliminary approval for the use of caffeine as an emergency frog control measure. Only licensed pesticide applicators are allowed to spray caffeine solutions for frog control, however, and officials warn homeowners not to experiment with other pesticides which could harm native species.