Rainy Summer Nights Bring Frog Calls Across Sanibel

by SC Reporter Reese Holiday

A pig frog. SC photo by Kyle Sweet

Using unique mating calls and sounds, frogs of different colors, shapes and sizes have made Sanibel a home to breed and to do their part in saving the environment.

Chris Lechowicz, Sanibel Captiva Conservation Foundation Wildlife & Habitat Management Program director, loves to hear these calls at night, and explained that amphibians, like frogs and toads, are great indicator species for water quality and environmental problems.

“Since their skin is very absorbent, they take in water constantly, as well as any toxins,” Lechowicz said via email. “A reduction or total loss of a frog species in a wetland can mean some type of environmental contamination has occurred, loss of water quality, or habitat change.”

He added that some amphibians are more tolerant of contaminants than others, and that the loss of a really sensitive species can mean the beginning of an issue for a wetland habitat.

Sanibel is made up of many of these wetland habitats, as well as many other areas of southwest Florida, which is why surveys are conducted all over the region to gauge the population numbers for frog and toad species that call these areas home.

The Southwest Florida Amphibian Monitoring Network conducts their FrogWatch program every year during the rainy months of June through September where biologists and volunteers across the region put their ears to the night sky and listen closely for frog calls.

Green Tree Frog. SC photo by Kyle Sweet

Since the early 2000s, Lechowicz has led the charge for Sanibel’s surveys where he and his crew go to 20 locations around the island, most of them wet, to listen and record the calls of the island’s nine frog and toad species. These include the Narrow Mouth toad, Southern toad, Cuban treefrog and Green treefrog, just to name a few.

These surveys are all conducted on the third Wednesday of each rainy month where frogs and toads will call out during the night to find a mate so they can lay their eggs in a body of water.

But it’s not just any body of water as Florida’s showers provide these slimy creatures with temporary bodies of water to lay their eggs in, also referred to as ephemeral wetlands.

Some frogs and toads will lay their eggs in permanent bodies of water, like lakes and rivers, but that doesn’t provide the same advantage as temporary spots.

“The advantage of laying your eggs in temporary water is that when those eggs hatch, and they turn into little tadpoles, there’s no fish predators in the water, or very few,” Lechowicz said. “Permanent water, you have fish all year round. Temporary water, it takes a lot for fish to get in there.”

But whether the frogs’ nests are temporary or permanent, surveys of all kinds of frog species don’t just occur in southwest Florida.

Much like this region, the country as a whole has its own network for these frog surveys called the North American Amphibian Monitoring Program.

Findings in southwest Florida, like call intensity, temperature and humidity, will first be reported to SFAMN. This data is then shared to the NAAMP, which also collects data from other participating regions across the country.

Each region will have different species with different calls, but the nation’s surveyors will all go out and listen on the same Wednesday of each rainy month. Lechowicz explained that data collectors must go out on a set schedule and not just when the frogs are calling.

“That’s not an accurate way to record density over time,” Lechowicz said about going out when the calls are popular. “It’s a good way for presence and absence, to know if they’re there or not. But to really look at the population, you really have to have a schedule that you’re there at the same time every time that you go out.”

Schedule or not, Lechowicz said some nights are quiet, but most are filled with different kinds of calls. He added that the calls of the different species on Sanibel are all distinct from one another. Some make noises, like clicking or singing, and others don’t even sound like frogs at all.

“They are very easy to tell from each other,” Lechowicz said about the calls of Sanibel’s amphibians. “One or two of them might sound a lot like insects to some people, but after you hear it enough times, it doesn’t sound like an insect anymore.”

Some calls are more popular than others. Lechowicz said the Cuban treefrog, an invasive species to Florida, is typically dominant on the island and can be heard often throughout the summer. Compare this with the Squirrel treefrog, which Lechowicz said he hasn’t heard in about five years.

Lechowicz credited their gradual exit to unnatural predators, like the Cuban treefrog, and emphasized the importance of surveying during the summer. He said collecting data on these frogs can indicate the decline of certain species, as well as warn of potential environmental issues to come.

Collecting different types of information during the summer nights can provide scientists the data that they need on frogs, toads and other amphibians.

But putting an ear to the sky and listening to a chorus of calls can also make surveyors feel more with the environment around them.

“I love hearing the frogs at night,” Lechowicz said. “It just makes me feel like I’m in nature.”

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