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Invasive frogs starting to shatter California's quiet nights

About a dozen scientists and volunteers were hunting through the foliage of a tropical plant nursery recently in Torrance. Their prey, the tiny yellow-brown coqui frog, had invaded the business a couple years ago. The researchers were trying to capture as many frogs as they could to get a sense of how well the frogs were reproducing.

It was a warm night, and the adult males were singing in force, trying to attract mates. Their shrill calls of “ko-KEE” filled the room and were audible from the street. If the frogs are able to escape the nursery and establish themselves, they could change the sonic landscape of nighttime in Southern California.

A male coqui frog hides within a plant at a tropical nursery in Torrance.
Jed Kim
A male coqui frog hides within a plant at a tropical nursery in Torrance.

“In general, we don’t like the idea of having these non-natives around. But these ones, we already know they have a couple of strikes against them, which is why we don’t want to see them getting established here in California,” said Greg Pauly, curator of reptiles and amphibians at the Natural History Museum of Los Angeles County.

By the end of the night, the team at the Torrance nursery caught about 100 of the animals — the largest, about the size of a quarter; the smallest, a small pebble. Plenty more, however, remained, their singing still evident, though slightly muted.

Three established populations of coqui frogs currently exist in Southern California: one in Torrance, one in Orange County and one in San Diego. All are at nurseries. Though the frogs are native to Puerto Rico, they are believed to have come to California on tropical plants from Hawaii.

“It’s hard to know exactly how they’re getting here, but it certainly seems like the nursery plant trade is one major source," Pauly said. "And I’ve talked to people who run nurseries, and one nursery that I work closely with, their species list of non-native reptiles and amphibians over the past five or six years is over 10 species.”

The potential for noisy nightS can be seen (well, heard) in four of Hawaii’s islands. Coqui frogs reached the islands in the late 1980s, most likely on tropical plants shipped from Puerto Rico.

With no natural predators, the frogs’ populations have exploded. Millions of dollars have been spent on efforts to eradicate the invaders, but those attempts have largely failed. Plagued residents are simply getting used to their loud neighbors.

William Mautz, a researcher at the University of Hawaii at Hilo, has recorded coqui calls at 73 decibels, the equivalent of a noisy party. He said the change in just a few decades is remarkable.

“We don’t have many singing insects or other frogs, and so the nighttime in the Hawaiian forests are very quiet. That’s what people grew up with and were used to, and they liked the quietude, and suddenly with the dense populations of these frogs, that was shattered,” Mautz said.

Southern California's coqui frogs are quieter during the winter, but as weather warms, researchers are asking residents to keep an ear out for the calls. That information will help them know whether the population is spreading.

Prevention, not eradication

There are several reasons it is so difficult to eradicate coquis once they’ve become established. The tiny animals are able to shelter in the myriad hidden nooks found within a plant. More than that, however, is the fact that the frogs don’t require water in order to reproduce — their young skip the tadpole stage and hatch as tiny frogs. That means an undetected egg mass that reaches a suitable habitat can lead to a successful population.

“Once they become established, trying to deal with them is really hard, and that’s why we always push prevention,” said Jennifer LaBay, a former senior environmental scientist with the California Department of Fish and Wildlife’s invasive species program.

Coqui frogs are a restricted species in California. Incoming shipments of plants are inspected for such species, but Pauly said it’s inevitable some unwanted visitors will slip through.

“It’s pretty worrisome. I think without some changes in the process of exporting plants from Hawaii or some changes on the inspection side here, I would expect that the frogs are going to continue to come in, unfortunately,” Pauly said.

He said it’s not the noise that worries him as much as the frogs’ potential impacts on the ecosystem.

“My concerns are not really about how well people sleep at night. It’s about what parasites and diseases and funguses they could be bringing with them that could cause our native species a problem. That’s my real concern,” Pauly said.

A few factors could keep the coquis from spreading successfully. The tropical species needs frequent rainfall in order to survive. Those conditions are not found in Southern California outside of nurseries.

“The good news is that these frogs need pretty moist conditions, and here in Southern California we have a prolonged period of dry every year. And so if it was just out in a yard that’s not getting regular irrigation, they probably aren’t going to make it, Pauly said.

“But let’s say they show up at a hotel where the hotel is watering their non-native tropical vegetation three times a week. Well, then they can get established,” he added.

A new noise

That said, some coquis have escaped from nurseries.

There have been two instances in the past few months of a male frog singing people to distraction. One instance occurred in Long Beach and the other was in Beverly Hills. Pauly said the Beverly Hills frog caused neighbors to call the police, because they thought the sound was coming from a car alarm.

“It was driving people crazy, and so you can imagine that if these frogs got established in some neighborhoods, there’s absolutely a chance that it would, for example, drive down property values, because they’re just so loud, and people aren’t going to want to live there, because they can’t go to bed,” Pauly said.

Others, however, may actually welcome the sound.

Suzan Hubert, a homeowner in Torrance, was the first to notify researchers of the frogs at the nursery. She originally thought the calls were coming from a strange bird. She and a colleague sent a recording of the calls around the birding community. The recording eventually reached Pauly.

Hubert said she enjoys hearing the frogs when they start singing in warmer months.

“I think they’re lovely. I listen for them every summer. They tell me summer’s coming now,” Hubert said. “When I hear the coquis, it’s, ‘Oh hey, it’s summer!’”

She hopes others in California will come to celebrate the coqui frogs as much as Puerto Ricans do. She wrote an article for the Friends of Madrona Marsh newsletter, in which she shared the translation of a Puerto Rican folk song dedicated to the frog:

Little coquí frog how I love you.
How I love your beautiful song.
In the night as I am sleeping,
You sing to me all night long.

Chorus: Coquí, coquí, coquí, I hear you singing to me.
Coquí, coquí, coquí, I hear you singing to me.

“I suppose one person’s noise is another person’s music,” Hubert said.