Hawaii Island’s nonnative birds might have found a friend in the coqui frog.
A new study on coquis, an invasive species known for its piercing two-tone chirp, noted a connection between the abundance of the small frogs and higher populations of introduced birds in a forest.
However, the frog’s population density did not appear to be a factor in the number of native birds documented, according to the report published by the American Ornithological Society, which looked at 15 sites.
The Utah State University researchers note that nonnative birds are “generally undesirable” because they transmit disease and prey on native species. Increasing their numbers could “induce undesirable ecosystem impacts,” the report says.
It has been hypothesized that coqui frogs could harm native bird populations by competing for insects. Most native birds forage on insects in the canopy and understory, while coquis are more likely to forage in leaf litter, the report says.
“Because we did not find a negative association between coquis and any bird species, our results suggest that apparent competition is not having a significant effect on bird abundances in our sites,” the researchers wrote. “The native species that we observed co-occurring with coquis in our mostly lowland sites are those that are most resistant to avian malaria and poxvirus. If coquis continue to invade higher-elevation forests … they could have impacts on the more location-restricted native birds that we did not observe in our study.”
Coquis could be helping nonnative birds either as a novel prey item or impacting the ecosystem in a way that benefits them, such as by changing insect populations or increasing nutrient cycling, the study says.
Researchers note coquis and nonnative birds might be aided by something in the environment the study didn’t measure, though they don’t think that explains the patterns.
Populations of coquis on Hawaii Island far exceed those found in their native Puerto Rico since being introduced in the 1980s via the nursery trade. In some locations, they can reach 91,000 frogs per hectare, which is about 2.5 acres, according to the study.
Email Tom Callis at tcallis@hawaiitribune-herald.com.
