The coqui frog must be having a big impact on something it feeds on, because there seem to be a lot of them.
Beloved in Puerto Rico but driving people nuts in Hawai'i with its piercing nighttime calls, the coqui tree frog has invaded a number of habitats, and not a few back yards, in the Islands.
It has been vilified as a potential predator of native insects, although some folks suggest it might actually be a benefit, because it could reduce populations of invasive pest insects.
Which is it?
Maybe a problem for natives, but it doesn't seem to be much help with pest species, writes Utah State researcher Karen H. Beard in the May 2007 issue of Copeia, the quarterly journal of the American Society of Ichthyologists and Herpetologists. Beard studies the invasion of coqui frogs through their impacts on the environment, Her paper is entitled, “Diet of the invasive frog, Eleutherodactylus coqui, in Hawaii.”
To determine what impact the coqui might be having on insects, Beard went out to 11 sites on Maui and Hawai'i and collected hundreds of frogs, as well as collecting bugs and other creepy-crawlies from the same areas.
In comparing frog stomach contents with what she'd found in the environment, she concluded that the frogs are mostly feeding among the leaf litter.
They are also opportunistic, meaning their food sources change based on what's available.
But generally, they seem to do a pretty good job on ants, which aren't native to Hawai'i and which make up 30 percent of their food. Next most common are types of amphipods, relatives of shrimps and crabs, sometimes called landhoppers, which may or may not be native. The endangered Kaua'i cave amphipod, which lives in cracks and lava tube caves in the Koloa region of Kaua'i is in this group, so there are native animals in this group.
Beard's review found a higher proportion of the ants and amphipods in the frogs than in the environment, suggesting that the frogs key in on these species.
But they'll also eat mites, beetles, flies and other little critters
If anyone was hoping the frogs would be going after really annoying pests, like mosquitoes and termites, no such luck. Beard found no mosquitoes at all, and while termites were present, they represented less than one percent of the frogs' prey.
Beard concluded that endemic species—ones found in Hawai'i and nowhere else on the planet—may be at risk from the coqui, and that more research should be done in areas where endemic populations are high.
“It is these locations where E. coqui may have the greatest impact,” she wrote.
To learn more about the frogs, see www.hear.org/AlienSpeciesInHawaii/species/frogs/.
© 2007 Jan W. TenBruggencate