A bizarre fish that lives in the San Francisco Bay has been singing, and it has been baffling scientists, until now. The male Porichthys fish, also called the plainfin midshipman fish, has been keeping people awake around the Bay Area with its incessant singing — likened to a chorus of kazoos or the drone of bees — for years, and scientists hadn’t been able to figure out why they sung only at night and then stopped before daybreak.

But a new study out of Cornell University claims that melatonin, that chemical we credit for making us sleepy at night, may be the cause. It’s a fascinating discovery because for many years scientists had known other animals had melatonin, but couldn’t figure out what it was used for. It certainly didn’t seem to make nocturnal animals sleepy, after all.

As it turns out, melatonin isn’t exclusively a sleepiness agent. It may simply be a trigger for nocturnal behavior. For us, it triggers the nocturnal behavior of sleeping. For the Porichthys, it triggers the nocturnal behavior of seeking a mate.

The discovery could help scientists better understand the nocturnal behaviors of many animals behind the Porichthys, and the function of melatonin in general.

“Our results, together with those of others that also show melatonin’s actions on vastly different timescales, highlight the ability of hormones in general to regulate the output of neural networks in the brain to control distinct components of behavior,” said Andrew Bass, professor of neurobiology and behavior in the College of Arts and Sciences, the paper’s senior author. “In the case of melatonin, one hormone can exert similar or different effects in diurnal vs. nocturnal species depending on the timescale of action, from day-night rhythms to the duration of single calls.”

“Melatonin is an ancient and multifunctional molecule that is found almost ubiquitously in the animal kingdom,” said Ni Feng, Ph.D. ’16, a former graduate student in Bass’ lab who is currently a postdoctoral researcher at Yale, the paper’s first author.

“Similarly, circadian rhythms govern the daily lives of diverse lineages, from plants to animals,” Feng said. “Our study helps cement melatonin as a timing signal for social communication behaviors.”