Researchers have eavesdropped on the love songs of many kinds of creatures, from the great whales to birds, frogs and crickets. Now they have recorded the love whispers emanating from the wings of the lowly fruit fly.

Each species of fly has a distinctive call, created by the males' wingbeats and intended to stimulate the female to mate. The wingbeats are made in regular, repeating pulses, and those pulses come in rhythms.

C.P. Kyriacou at the University of Edinburgh, Scotland, and Jeffrey C. Hall of Brandeis University found in studies reported in the April 25 issue of Science magazine that females listen attentively to both pulse and rhythm, and are not attracted to all males' signals.

One species has wingbeat pulses every 35 milliseconds and a rhythm that fluctuates every minute or so. Another's pulse is every 50 milliseconds, with a rhythm cycling every half-minute.

Kyriacou and Hall crossed these two species to see how females would react. Their work shows that the rhythm and the pulse are controlled by separate genes.

The rhythm is controlled by a gene inherited from the mother. So, as Science notes, "In this feature of the song, male fruit flies want a girl just like the girl that married dear old dad."

The pulse is controlled by another gene, and the pulses of the hybrid are halfway between the love pulses of the two species.

What does the female do when confused by such mixed signals? Unfortunately for the hybrid males, the female, hybrid and otherwise, does not prefer their song. She responds best to a song that has both rhythm and pulse like those of the mother species. Or, alas, she responds even more strongly to an artificial song with pulses and rhythms between the two species and created only by the researchers.