The singing mouse

For a long time, the world of rodents has been considered a very quiet world, but new research has found that this world is full of "song".

Rats can "sing" like birds - it sounds unbelievable, but it's true.

In late 1925, J.L Clark found an unusual mouse in a house in Detroit, USA - it would "sing". He caught the mouse and put it into a cage. The mouse in the cage issued a lyrical tone, like a bird in the "song". Clark gave the mouse to researchers at the University of Michigan, who studied it and concluded that the mouse could indeed "sing". Next, they mated the rat with laboratory mice, and their offspring produced a muffled "chirp," but none inherited the melodious, lilting tone of their father. These observations were all recorded in a scientific paper in 1932, but as time passed, the papers were almost forgotten.

Recently, University of North Carolina biologist Martina again studied the mystery of mouse "singing". After mastering how to listen to the "mouse version of the song," she heard something completely new.

To capture the "song" of the mouse, Martina, and her students did a lot of preparation work. At night, they brought their luggage, notebooks, scales, laptop computers, and recording equipment to a pine forest, wearing helmets. They connected six long cables to a loudspeaker and placed the loudspeaker where they thought the rats were likely to chant, thus forming a listening network. The forest they chose was not very large and not very primitive, it was surrounded by corn, tobacco, and cotton fields. But for them, it was perfect enough. Because they wanted to listen to the mouse solo, not a symphony of animals, and the pine forest is very quiet, with no insects and other singing creatures on the ground. In order not to disturb the singing rats, they carefully crossed a log lying on the ground, came to a torch pine, and connected the amplifier.

Martina worked as an intern at the age of 19, specializing in the study of bat behavior. Obsessed with this research, she often came outdoors in the middle of the night and stayed overnight. She is now a behavioral biologist and an expert in animal sound communication. To date, she has accumulated thousands of hours of late-night work in the forest. She can identify the click of a bat, the scrape of a weaver, and the "croak, croak" of a frog, all of which escape her keen ears. She gradually became an expert in sound identification. Of course, occasionally she encounters sounds that she cannot identify.

Since 1996, Martina has been leading a study in Monterey County, North Carolina, to find out if two species of mice in the area call to each other and make gibbering noises. One night, she thought she heard the rats' "song" and they made a sound just within the edge of her hearing, just as a seaman can dimly detect land far over the horizon.

In 2004, Martina borrowed a hand-held tape recorder that recorded ultrasonic scattering, and she brought the instrument to her research field in North Carolina. As part of her animal behavior research, she captured many rats, marking them on the ears before releasing them. Not only was she able to remember the names of many of the rats, but she also knew where they lived. She placed the recorder in the places frequented by these rats and waited patiently.

After waiting for one long night after another, the researchers brought the recorder back to the lab. They listened to the slow-play recordings through headphones, and the slow-play recordings reduced the sound frequency. If there are new findings, they use the computer to convert the recording into a sound spectrum, a kind of sound frequency graph with high and low changes. As a result, they heard an unusual sound.

It was a very high-frequency scream, they used the computer to analyze, and as a result, they saw a completely new graph. It was a four-tone singing sound and it was coming from a mouse. It sounded a bit like a whale's courtship song, with a melancholy tone and a distinct change in pitch.

Martina has now translated the ultrasonic vocalizations of rats obtained from North Carolina and is translating the vocalizations of rats in the northeastern United States. Her findings suggest that some songs are produced only by male rats and others only by females; even between two closely related species, their songs may be very different, just as robins and wrens have widely different songs. These differences may help the rats recognize each other.

Martina also found that the songs of some species of rats become more complex as they age. The rats' songs may be innate, and in the experimental rats, the mice raised by rats with different singing voices still maintained their own "singing" style. Martina and her students have now figured out the vocal method of four species of wild rats, and she suspects that many other species of rats can also sing. While the rodent world has long been considered a very quiet world, Martina's research has shown that it is full of "song. Through "song", rats can communicate with each other over short distances, but we do not know much about the meaning of their "song".

Martina's discovery has led to a new understanding that each species has its unique way of perceiving the world. Bacteria call each other through chemical elements, mosquitoes can detect the carbon dioxide we exhale, ants can see polarized light, turtles can navigate using the Earth's magnetic field, birds can see the ultraviolet patterns on flowers, and snakes can track the trace heat source emitted by a cigarette or a rabbit. We still know very little about the different ways in which living things perceive the world, due to the limitations of our human perceptual abilities.

Following Martina's discovery, Japanese scientists have also experimentally confirmed the existence of "singing" mice. Japanese scientists have recently modified a group of "singing" rats. In the experiment, they crossed many generations of genetically modified mice, and then examined the newborn mice one by one until they found the mice that could "sing" like birds. So far, the lab has more than 100 "singing" mice. Previously, some scientists have found that birds use a variety of different sound elements, combining them into sound modules, similar to words in human language, according to certain language rules, and then further stringing the sound modules into "songs. Now, some biologists point out that rats are more suitable than birds for this research, because they belong to the same mammal as humans, and the brain structure of rats is also closer to humans. Scientists found that ordinary rats usually only when there is pressure to make a "squeak, squeak" call. They looked at how singing rats influenced ordinary rats in the same group, i.e. whether they could have a social influence. It turned out that when the mutant rats were placed in a new environment, or when males and females were together, their calls were louder. The scientists believe that their grunts may stem from some expression of emotion or physiological response.