Plenty of research has shown that human noise negatively affects how animals communicate, and there are vanishingly few places left devoid of any form of manmade din. But what about noise created by invasive species, introduced by people, that just won't shut up? The issue has scarcely been studied at all.
New research shows that in the presence of noisy calls from invasive Cuban tree frogs in south and central Florida, native green tree frogs double the rate of their calls, said Jennifer Tennessen, an ecologist and graduate student at Pennsylvania State University.
The results suggest that Cuban tree frogs, and perhaps similar noisy invasives, could have unforeseen ecological effects. Tennessen says that by doubling its call rate, the green tree frog makes its presence more obvious, which is likely to make it more vulnerable to predation.
In the study, the results of which are being presented June 6 at the International Congress on Acoustics in Montreal, Tennessen and her colleagues played recordings of the Cuban tree frog in the presence of wild green tree frogs and pine woods tree frogs at 23 different sites throughout Florida.
The former were chosen because their call is similar to the Cuban's; pine woods frogs were chosen as controls since their call is quite different, using different frequencies, or pitches.
The researchers hypothesized that green tree frogs would alter their call in the presence of the invasive animals, and they turned out to be right. Also as predicted, the pine woods frogs' calls remained the same.
During the study the scientists recorded calls from the native species before, during and after recordings of Cuban frogs. They also recorded reactions to white noise as a control, which had no effect.
Green tree frogs only changed their tune while the alien species were singing, Tennessen said.
Unlike all native tree Floridian frogs, the Cuban species also eat other tree frogs. There is a chance that green tree frogs' response to the Cubans—doubling their call rate—makes them more likely to be eaten by the invasive creatures.
Tennessen stressed that this study is preliminary, and her group is still analyzing other elements of the recordings to find out if the green tree frogs might have changed their tune in any other ways; for example, making it louder.
The study also only relied on recordings from three different green tree frogs, which limits the strength of any conclusions, although the results were significant, she said.
The researchers had planned to record more of the animals, but were stopped short by the presence of a potential human predator. “We ran into some alligator trouble and needed to prematurely conclude,” Tennessen said. Such is a risk of wading around South Floridian ponds at night. She plans to continue the study in the near future, and this time to use a small boat to prevent run-ins with alligators—although she said nobody was hurt, the alligators just got too close for comfort.
Cuban tree frogs arrived in the 1920s, probably hitchhiking about cargo containers on ships from Cuba. They eat at least five native species of frogs and have been spreading throughout the state ever since—they are now found almost as far north as southeastern Georgia, according to the University of Florida.
Their call can be described as a "raspy grating squawk," Tennessen said. The green tree frog sounds more nasally, and has distinct individual calls.
Would you be in favor of thinning out Cuban tree frog populations in Florida if it's determined their presence is too harmful to native species? Let us know what you think in the Comments.