To understand why, 200 years after his death, Mozart's "Musikalischer Spass" suddenly stands in controversy, it first must be understood that this is not at all a typical Mozart composition.

Translated to English, "Musikalischer Spass" is "A Musical Joke." The opening movement is a grotesque pastiche, a later cadenza goes on endlessly, horns come in wildly and veer off key, the fugue is all wrong. Where the boy genius would naturally be "perfect and elegant," says University of Chicago Mozartologist Martha Feldman, "this is a mess."

It must also be understood that the European starling is not the nondescript and disreputable flighted creature it is now taken to be. Starlings, in fact, are as gifted at mimicry as parrots or myna birds. In close contact with humans, they will pick up words and phrases and repeat them clearly and distinctly. They will sing and even dance along with music, memorize and repeat whole phrases of melody, and combine them in a joyous and spontaneous cacophony.

These gifts are underappreciated today, when the 200 million-plus starlings in the United States are largely considered urban eyesores and agricultural pests. But in Mozart's day, the bird was something of a celebrity. Mozart, in fact, kept one as a pet for three years, and was so devastated when his bird died that he staged an elaborate funeral, singing hymns and reading a poem he wrote in the bird's memory to the gathered crowd of heavily veiled mourners.

"A little fool lies here

Whom I held dear

A starling in the prime

Of his brief time."

In the volumes of Mozart scholarship written since the late 18th century, these rather eccentric facts about Mozart's life have been subjected to the most rigorous scrutiny. For some scholars, for example, "Musikalischer Spass" is a complicated psychological expression of Mozart's conflicted views toward his recently deceased father, Leopold, a kind of manic counterpoint to the saturnine operatic masterpiece "Don Giovanni."

Alternately it has been considered just what Mozart called it -- a joke. "This is a generalized manifestation of Mozart's musical humor," said New York University Mozart expert Cliff Eisen. He described the piece as an elaborate parody of the inept composers who flourished during the same period, reflecting what Mozart scholar Alfred Einstein calls "horseplay expressed in music."

And the bird? Well, Mozart scholars have unearthed letters written home by the composer inquiring on the status of his dog, Bimperil, and know from accounts of his childhood that he once had a pet canary. He was, in short, an animal lover.Scholars Spurn New Theory

Today, however, in the bicentenary of the wunderkind's death, two Indiana University psychologists have proposed a radical new theory. "Musikalischer Spass," they say, was actually a tribute by Mozart to his pet starling.

This suggestion, understandably, has been greeted coldly by the legions of Mozart scholars, few of whom are accustomed to taking interpretative cues from the species Sturnus vulgaris. But based on their research on the musical and mimetic habits of starlings, the researchers say their evidence is undeniable.

"When we listened to that piece for the first time, we looked at each other and said, 'This has starling written all over it,' " said Meredith West, who with her husband and fellow researcher Andrew King published the revisionist "Musikalischer Spass" theory last year in the magazine American Scientist.

The vocal abilities of starlings have earned them favorable mention from a variety of authors ranging from the Roman historian Pliny to Shakespeare, who had Hotspur muse about teaching a starling to say the word "Mortimer" to Henry IV. Deciphering the patterns of starling mimicry, however, has been difficult, because of the sheer volume and variation of the birds' songs.

King and West followed the development of 14 captive starlings over a number of years, closely recording the type and variety of sounds the birds mimicked. Their first conclusion was that the quality of starling mimicry is very high.

"When I play a tape of a starling, people always ask which voice is the bird and which is the human," said West.

The birds are also quite sophisticated. One would repeatedly yell "Defense!" when the television was turned on, a reaction apparently picked up from humans watching basketball games. All the birds showed the ability to master not just words or snatches of music but long phrases. One legendary bird, known as Rod Starling, was able to provide the entire message for his master's telephone answering machine. Rod Starling was also an enthusiastic proponent of the Rolling Stones, and would shuffle his feet and sing along vigorously whenever "(I Can't Get No) Satisfaction" was played.

Birds' Distinctive Vocalization

The birds have several distinctive vocal traits. They have no respect for phrasing. One bird would deliver an aching rendition of Stephen Foster's "Swanee River" but stop abruptly after "Way down upon the Swa---." Another, showing an almost post-modern flair, would mix and match from songs in his repertoire, routinely pounding out a rousing version of the "William Tell Overture" that segued into "Rockaby Baby." Few birds sang in key. Snatches of music were repeated endlessly.

West and King point out that Mozart's pet starling was as gifted as their experimental birds. When the composer purchased his bird, he wrote down a tune he had heard the starling sing, exclaiming "Das war schon!" (That was beautiful). Comparison of the bird's four-bar stretch and the beginning of the last movement of Mozart's own Piano Concerto in G Major shows the two to be almost identical. Experts are divided on whether Mozart picked up the sequence from the bird or the bird picked it up from him.

The two psychologists surmise that in the course of living with Mozart the bird became a valued collaborator, winning the composer's heart with irreverent and hilarious versions of the tunes that Mozart was composing and whistling in his apartment.

Where music scholars hear in "Musikalischer Spass" a wicked parody of the very worst in late 18th century composition, West and King hear a tender and brokenhearted eulogy to his dead friend.

"It is extremely repetitive," said West. "Various things go on far too long. He'll start a theme and then repeat it and repeat it. At some point the horns go off key, and the piece ends with the instruments stopping in mid-note like someone punctured all the instruments. . . . These are all the things that starlings do."