In Science's letters, Alex Ross saw some older research on birds listening to music mentioned. I decided to read the original articles. In the 1999 study, Keio University psychologists Watanabe and Sato trained Javanese sparrows within two groups. One group of four birds was encouraged to stand on their response perch only when Bach's French Suite, BWV 816, was played. They received a food reward when they moved to the response perch when the Bach was played, and were punished with a blackout of the lights if they landed on the response perch when Schoenberg's Suite Op. 25 was played. The other group of three birds was trained in the opposite direction, encouraged to respond to Schoenberg's Suite. This training lasted through a minimum 40 successful trials for each bird, until an 80% correct response ratio was achieved. One bird in each group was not able to achieve 80% correct response ratios within 60 sessions, and were dropped from further testing.
After this training the five remaining birds were exposed to Bach's Orchestral Suite, BWV 1068, and Schoenberg's Five Orchestra Pieces Op. 16. Positive food reinforcement continued for each relevant group, and all but one bird were able to discriminate the new Bach and Schoenberg to a significant level. That one bird who couldn't discriminate was in the Bach group. A second test replaced the Bach music with Vivaldi's Violin Concert in A minor, RV 356, and Schoenberg's music with Elliott Carter's Variations for Orchestra (1955). All five birds were able to distinguish between these new pieces successfully. The authors note here that a 1984 study by Porter and Neuringer showed that pigeons were able to generalize from Bach to Buxtehude and from Stravinsky to Carter and Piston.
Another interesting result was that two birds who had not shown any preference between Bach/Vivaldi and Schoenberg/Carter were still able learn to discriminate between the two types of music. Thus the lack of preference was not from a lack of ability to tell the difference, but rather from personal taste.
S. Watanabe and K. Sato, "Discriminative stimulus properties of music in Java sparrows." Behavioural Processes, 47 (1999), 53-57.