Scientists from Utah State University carried out research at 15 sites in Hawaii, in an attempt to discover if non-native coqui frogs were present and in what numbers.
The team also conducted bird surveys, and discovered that while native bird species were unresponsive to coqui presence and density, three of the 15 non-native species were more abundant in areas where coquis were present.
It has been suggested that coquis and native, insectivorous birds on Hawaii are not in direct competition for food as previously thought – coquis forage in leaf litter, birds in the canopy and understory.
“I was very surprised with the results for the birds,” says Dr Karen Beard. It had been hypothesised before our study that coquis would compete with birds, particularly natives, because we knows that coquis reduce insects where they invade.”
“In retrospect, I guess it’s not too surprising that predation is a more important interaction than competition. We’re pretty sure that some of this increase is due to these species eating live or dead coquies, and this novel resource appears to be increasing their populations.”
The coqui frog from Puerto Rico was introduced to Hawaii by accident in the 1980s, and today there are as many as 91,000 frogs per 0.01km2.
Instead of competing with each other, the findings show that it is more likely for non-native birds to prey directly on coquis or the flies that are drawn to the frogs’ carcasses and excrement, which contain extra biomass.
The discovery that the abundance of some non-native Hawaiian birds is in correlation with invasive coqui frogs is surprising and conjures more intriguing questions.
Perhaps the most significant question that springs to mind is what the true impact of other invasive species could be, and whether they are as detrimental as previously thought.
Main image: The coqui frog is native to Puerto Rico, but was accidentally introduced to Hawaii. © Wild Horizon/Getty