There are small, frozen frog in the woods of New Hampshire in the winter. The frozen wood frog is alive and well. The ice cube is suspended in animation.
The frog begins to thaw from the inside out. Their hearts were beating. Their blood is moving fast. They hop out of the leaf litter to find a mate.
The Frogs, as big as stroopwafels, paddle around the surface of the water, inflating their vocal sacs and calling out to females in earshot. On a clear day, it looks like it's raining in the pond.
From a distance, they sound like a flock of geese.
The slimy bachelors form a chorus, which female frog rely on to find mates. It is not possible to distinguish one singing frog from another because of the loud chorus. The unanswerable question was: What does a female frog find sexy?
In a paper published in the journal Ecology Letters, Dr. Calsbeek, Dr. Symes and Francisco Javier Zamora-Camacho tried to answer the question. With the help of an acoustic camera, they teased out the songs of individual males and began to untangle choruses that appear to humans and other animals to be a lot of chaos and noise.
Lindsey Swierk, who was not involved with the research, said that the scientists had offered "fantastic insight" into the calls of individual frog.
In the past, some wood frog researchers tried to eavesdrop on the choruses with a variety of devices. The overall sound of the pond was picked up by these devices. All humans needed a fancy acoustic camera. The ring-shaped frame of the Ring 48 AC Pro camera is similar to a Ferris wheel with small microphones.
Allison Sacerdote-Velat, the curator of herpetology at the Peggy Notebaert Nature Museum in Chicago, was not involved with the new paper.
The researchers took the camera, battery, and cable to the woods near the campus. Dr. Calsbeek dropped a tennis ball into the water to make the chorus restart.
Dr. Calsbeek said that the video showed a heat map of the pond with individual frog calls. The videos were difficult to analyze because they captured 25 to more than 150 frog in a single video that was constantly swimming around the pond. They found that individual frog calls were timed to follow their neighbors.
The researchers went back to the ponds to record the number of egg mass the size of softballs that had been laid in the pools to see which choruses females preferred.
The researchers used the individual calls they got from the wild ponds to conduct tests in the lab. A female frog was able to pick between two choruses during the trials. Females preferred calls with lower pitches. A bigger male is usually indicated by these deeper calls.
This preference didn't hold up in the forest. Ponds with males whose voices formed a chorus with little variation in overall pitch, regardless if the pitch was low or high, ended up with more egg mass. The females preferred the sound of the chorus, according to Dr. Calsbeek. Dr. Swierk warned that the causes of the observed patterns are still up in the air.
The logic and desire that leads a female frog to a specific pond disappears when she arrives, and a melee ensues as males race to cling to her in a tight embrace called amplexus. Multiple males will attempt to mate with a female that is already amplexed, or even a tiger salamander.
Dr. Sacerdote-Velat and Dr. Swierk hope that the acoustic camera can be used to observe reproductive behavior in other species of frog where females have more ability to discriminate between and choose their mates.
Wood frog females are known to have more decision-making powers than previously thought. Dr. Sacerdote-Velat said that the wood frog will aggregate over a former pond that has been paved over.
Dr. Swierk said that the paper's implication that females may choose where to breed complicates the assumption.
Even with these choices, wood Frogs don't have to hop too far.
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