Happy Nice Mall

In winter, the New Hampshire woods are full of small, frozen frogs. Although the heart of a frozen tree frog does not beat, the frog is not dead. In a suspended animation state: an amphibious ice cube.

As spring approaches, frogs begin to thaw from the inside out. Their hearts are beating. Their blood quickens. They jump through the leaf litter to find a mate, and often to the spring pond where they first hatched.

The frogs are as large as stroopwafels, paddling on the surface of the water, inflating their vocal sacs and calling out to any female frog within ear distance. Each frog cry creates small ripples in the water. “On a clear day, it looks like it’s raining in the pond,” said Ryan Calsbeek, an evolutionary biologist at Dartmouth.

“From afar, they sound like a flock of geese,” said Laurel B. Symes, assistant director of the K. Lisa Yang Center for Conservation Bioacoustics at the Cornell Lab of Ornithology.

The cumulative calls of slimy singles create a distinctive chorus that female frogs rely on to choose a pond to mate with. The choirs are so muffled that it is impossible to distinguish one singing frog from another, let alone investigating which male voices are more attractive to females. Dr. For Calsbeek, that was the unanswerable question: “What would a female frog find sexy?”

In an article published in the journal March Ecology Letters, Dr. Calsbeek, Dr. Francisco Javier Zamora-Camacho, a researcher at Symes and Dartmouth, attempted to answer this question. With the help of an advanced acoustic camera, they extracted the songs of individual men and began to decipher the choruses that seemed like a lot of chaos and noise to humans and other animals.

Lindsey Swierk, a behavioral ecologist at Binghamton University who was not involved in the research, said the scientists offered “great insight” into the calls of individual frogs in the chorus. Dr. “There’s definitely some logic to the frog’s eye,” Swierk said. “It’s us humans who have trouble seeing examples.”

In the past, some tree frog researchers have tried to listen to these choruses with GoPros, shotgun microphones, and automatic call recorders. But these devices only captured the overall soundscape of a pool. It turned out to be a very fancy acoustic camera that all people need. Being a Ring48 AC Pro, the camera looks a bit like a Ferris wheel with its ring-shaped frame adorned with tiny microphones. Dr. “It’s like having 48 different ears,” Calsbeek said.

“I’m jealous of their field equipment,” said Allison Sacerdote-Velat, curator of herpetology at the Peggy Notebaert Nature Museum in Chicago, unrelated to the new paper.

The researchers connected the camera, its 45-pound battery, and about 75 feet of Ethernet cable to the forest spring ponds of the Dartmouth campus. To get all the frogs in the pond to sing, Dr. Calsbeek dropped a tennis ball (labeled “frog spook on Sharpie”) into the water to restart the chorus.

The resulting image was a video of the pond with a heatmap showing individual frogs’ voices. Dr. “Blink and you can see where the frog is,” Calsbeek said. However, Dr. Videos are still difficult to analyze, Symes said, catching more than 25 to 150 frogs constantly swimming around the pond in a single video. They found that individual frogs timed their calls to follow their neighbors.

The researchers then returned to the pools and recorded the number of egg masses the size of softballs deposited in the pools to estimate which choruses the females might have preferred.

The researchers also conducted tests in a lab using individual calls they extracted from wild ponds. Dr. Zamora-Camacho pioneered playback trials where a female frog could choose between two choruses. The trials found that women preferred lower pitched calls. These deeper calls usually indicate a larger male.

But that choice didn’t necessarily hold up in the woods. Pools of males whose voices form a chorus with little change in overall pitch, regardless of pitch low or high, are surrounded by more egg mass. Dr. Calsbeek said this could indicate that women prefer uniformity in the choral voice. Dr. Swierk cautioned that “the underlying causes of these observed patterns are still very much in the air.”

All the logic and desire that drives a female frog to a particular pond vanishes once she gets there, and a close fight ensues as the males race to hug her in a tight hug called an amplexus. Males are so desperate to mate that more than one male will unsuccessfully attempt to mate with an already enlarged female or even anything slimy and alive. tiger salamander. Dr. “It’s like a ball of frogs struggling,” Sacerdote-Velat said.

Dr. Sacerdote-Velat and Dr. Swierk said he hopes the acoustic camera could be used to observe reproductive behavior in other frog species, where females have greater ability to distinguish and choose mates.

But female tree frogs may have more decision-making power than previously thought. Dr. “Wood frogs are philopatric, which means most of them go back to breeding in the pond where they hatched,” Swierk said. Dr. Sacerdote-Velat said the tree frogs’ attachment to their burrows is so strong that the amphibians will congregate on an old paved pond.

Dr. Swierk said the new paper’s implying that females can actively choose where to breed complicates this long-held assumption.

Still, even with these options, tree frogs never have to jump very far. Dr. “They’re tiny sound-producing droplets and dry out quickly, so they tend to stay where they came from,” Symes said.