The recent talk of ultrasonic tarsiers reminded me of a post I wrote a couple years ago. You see, tarsiers aren't the only animal to communicate at a sound frequency beyond the level of human hearing: mice do as well. But, for some reason, some mice actually chatter in such a way that they can be heard by humans. While most mice are ultrasonic, as far as I can tell there's no good explanation for why some mice are...sonic. But this story begins one hundred years ago, in 1912, likely well before anyone knew about ultrasonic communication in mice.
Sometimes, when trolling through your institution's journal subscriptions online, you wander into a treasure trove. I happened upon such a treasure trove recently: The Journal of Animal Behavior, which was published for just six years, between 1911 and 1916.
The studies described in this journal were being conducted at a time when experimental psychology was just emerging as a serious scientific discipline. In 1881, for example, Wilhelm Wundt organized the first scientific journal devoted to psychological science. The first laboratory for experimental psychology was established at Yale University by George Trumbull Ladd in 1879. Thirty years on, some of the early giants of animal behavior were publishing in the Journal of Animal Behavior - scientists like Robert Yerkes (renown ethologist/primatologist), Karl Lashley (of engram fame), and John Watson (considered by many the founder of the school of behaviorism). To put this into perspective, Ivan Pavlov's experiments on the conditional reflex in dogs were conducted in 1901, just a decade prior to the first issue of this journal.
And so it is in the Journal of Animal Behavior that we find our hero: Charles A. Coburn, a graduate student at the Harvard Psychological Laboratory. He writes:
In the literature of animal behavior appear several references to the production by mice of sounds of musical quality. The "singing" of mice is described variously by different writers. Lee states that it consists of a series of chirps at the rate of three or four per second. At the beginning of the series, the chirps are low but gradually they become louder. The "song" of one mouse this author likens to the sweet and varied warbling of a canary. Every note was "clear and distinct."
In referring to the same phenomenon, the naturalist Brehm attributes the following descriptions to various observers. One informant states that the "song" is an irregular mixture of chirps and trills with here and there a snarling, smacking sound followed by a low murmur. Another describes it as a twitter which is a mixture of long drawn squeaking and piping sounds which may be heard at a distance of twenty paces.
One observer noted the phenomenon only in the case of a female mouse while giving birth to young, while another observer states that only the male sings.
It is not unusual, of course, for animals such as mice to emit sounds, but what was particularly interesting to Coburn was the musical quality of these chirps. What conditions would lead mice to vocalize in this way? Some scientists had assumed that the dulcet tones of these mice had to be due to some sort of disease or distress affecting the lungs or the any of the vocal organs, but others had blamed pregnancy or liver parasites.
Many scientific observations are the result of luck or happenstance, and on the evening of December 1, 1911, the young Mr. Coburn simply happened to be in the right place at the right time.
He describes his experience in the third person:
The writer desires to add to the observations already reported an additional record of "singing" mice. About the first of December, 1911, while working one evening in his study, he heard a series of sounds which seemed to come from above the ceiling. At the time, they were thought to resemble the soft chirp of a bird.
Shortly afterward, some wild mice were needed for breeding experiments and, by means of a trap, two mice, a male and a female, were captured in the room.
These animals, while being taken to the Harvard Psychological Laboratory, produced sounds like those previously heard in the room and they continued to do so at intervals after being placed in a laboratory cage.
Unfortunately for Coburn, but somewhat fortuitously for the rodent, the male mouse escaped, which meant that the female singing mouse was mated with a domesticated lab mouse. The singing diva subsequently produced thirty-three offspring in five litters. None of her progeny ever sang as their mother did, nor did any of her grandmice nor great-grandmice.
As far as Coburn could tell, the enigmatic singing female mouse was an ordinary house mouse (Mus musculus). He noted that she was "extremely active and savage, and her mate always bore the marks of her teeth." There was not any reliable way to predict when the singing would occur, though a pattern seemed to indicate that she would sing starting three to four days prior to the birth of her litter, through the sixth or seventh day following. "It was observed, also, that the individual 'sang' sometimes when frightened."
Coburn took pains to describe in detail the singing of the little performer:
The quality of the tone resembled somewhat that of a fife or flute, but each tone ended with a slight throaty click. The tones were uttered at the rate of four or five per second in groups of varying size. Sometimes, a group occupied one second, some- times as long as ten seconds. As a rule, the tones of a group were not clear and distinct but, instead, were-uttered so rapidly as to seem connected. The throaty click was more noticeable in the case of the last tone of a group. Often the "singing" would be continued for a period of ten or fifteen minutes with rests between groups.
The incredible singing mouse kept singing through June of 1912, but no further singing was heard following the first of July that year. In August, she died, likely of old age. But the following May, singing was again heard in Coburn's study: the very same room in which the singing mice had first been captured. Was it the escaped male mouse, singing the blues, mourning the loss of the other half of his crooning duo? Or was it perhaps the restless spirit of the deceased female mouse, reminding Coburn of the enduring mystery of the singing mice?
Science will likely never know.